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. 2025 Apr 14;20(4):e0315885. doi: 10.1371/journal.pone.0315885

The dynamic shape changes of the tongue base during respiration, chewing and swallowing

Doris Haydee Rosero Salazar 1,#, Zi-Jun Liu 1,*, Amy Ly 1,#, Yikang Dong 1, Alexander Veasna Simnhoung 1
Editor: Ayako Mochizuki,2
PMCID: PMC11996074  PMID: 40228018

Abstract

This study aimed to analyze dimensional deformations of the tongue base during respiration, chewing, and swallowing. Eight 7–8-month-old Yucatan minipigs were used. Under deep sedation, eight 2mm ultrasonic piezoelectric (SONO) crystals were implanted in the tongue base forming a cubic-shaped configuration, representing right/left dorsal and ventral lengths, anterior/posterior dorsal and ventral widths, and right/left anterior and posterior thicknesses. Next, 8 pairs of electromyographic (EMG) microelectrodes were inserted into the tongue, jaw, hyoid, pharyngeal, and palatal muscles. SONO and EMG signals during respiration were recorded. Then, minipigs were allowed to wake-up for unrestrained feeding. The feeding sessions were recorded with synchronized EMG and videofluoroscopy to confirm the phases of jaw movement in chewing, and swallowing episodes. Amplitudes, durations, and timings for each dimension of the SONO crystal-circumscribed region were measured from the start of the jaw opening. Findings during respiration showed elongated lengths, anterior widths and anterior thickness (p<0.05). For chewing, the width elongated up to 17% while the length and thickness shortened (12–33% and 10–32% respectively, p<0.05). Onsets of deformational changes in length and thickness occurred 10–30% earlier than in width. The cycle duration was 0.55 ± 0.11seconds chewing, and 0.69 ± 0.16seconds swallowing. During swallowing, the dorsal length (5–12%) and posterior width (10–14%) elongated whereas the posterior thickness (9–15%) and ventral length (4–10%) shortened. Explicit 3D-kinematic patterns in relation to specific functions characterize the tongue base deformation. The findings of this analysis will contribute to a better understanding of the oropharyngeal biomechanics upon abnormal conditions.

Introduction

The tongue base, a structure located from its posterior end to the terminal sulcus and the circumvallate papilla anteriorly, seems to be anatomically, physiologically, and functionally distinct from the tongue body (located from the terminal sulcus to the tip) [1]. The tongue base regulates the openings of the larynx and esophagus during respiration, swallowing, and vocalization [2,3]. Also, the movements of the tongue base seem to be synchronized with those of the jaw, soft palate, epiglottis, hyoid bone, and pharyngeal wall [4].

The implanted sonometric technique has been employed in vivo to investigate deformational changes and internal kinematics for real-time muscle contraction. Small SONO crystals were implanted in the muscle mass to measure the distance between crystal pairs at a determined speed of sound [5–8]. Deformational changes in thickness, length, and width were measured regardless of tissue stiffness, fat composition, or tissue fluids [5]. Previous studies on the internal kinematics of the tongue body during ingestion, drinking, and chewing indicated regional deformational changes [8–10]. For instance, variations in length, width, and thickness occur rhythmically stereotypically and synchronized with jaw movements. These studies demonstrated task-specific timings, directions (distance shortening or elongation), and amplitudes of the tongue body highly coordinated with the activities of the jaw, tongue, and hyoid muscles. However, these features in the tongue base are yet to be understood.

Our recent study in young adult minipigs using videofluoroscopy showed critical positional changes of the tongue base and other oropharyngeal structures in respiration, chewing and swallowing [11]. The major role of the tongue body in drinking, ingestion, and chewing was reported previously [10]. However, the internal kinematics of the tongue base during these functions is unknown. Therefore, the present study examined the 3D deformational changes of the tongue base in respiration and chewing/swallowing during sedated sleep and unrestrained feeding, respectively. We hypothesized that the internal kinematics of the tongue base are specific upon respiration, chewing in the pharyngeal region, and swallowing. The findings of this study are to contribute to a better understanding of the internal kinematics of the tongue base, and this will clinically support further insights into the mechanisms of respiration and swallowing disorders, such as obstructive sleep apnea (OSA) and dysphagia.

Materials and methods

Animals

The Institutional Animal Care and Use Committee UW reviewed and approved all experimental procedures (Protocol 3393-05), which were adhered to the ARRIVE guidelines. A total of healthy eight 7–8-month-old Yucatan miniature pigs (4 each sex, Premier BioSource, Ramona, CA) were used and housed one per pen. The minipigs were acclimated for 5–7 days after arrival in the new environment. Environmental enrichment and 12–24 hours dark/light cycles were provided per pen by the Animal Care Facility. Daily training on a custom-made feeding table started on day 3 and lasted until terminal experiments. The minipigs fasted overnight for up to 12–16 hours the day before recordings and their weights were monitored weekly.

Baseline recordings

Sedation with xylazine (4mg/kg), midazolam (0.5mg/kg), and butorphanol (0.3mg/kg) was used. Additionally, maintenance with isoflurane 2–3% in oxygen was provided. This recording involved the insertions of 8 pairs of 0.10mm wire electromyographic (EMG) electrodes (California Fine Wires Co. CA) into the left tongue (genioglossus and styloglossus), palatal (tensor veli palatini and levator veli palatini), pharyngeal (middle pharyngeal constrictor), hyoid (thyrohyoid), and jaw (masseter and digastric) muscles. Only the left side was used to reduce discomfort during chewing and the stronger masseter muscle activity burst indicated ipsilateral activity [12]. A mouth mask and nasal catheter (50mm inside of left nostril) connecting with an airflow sensor (TSD160A-TSD237F, BIOPAC Co, CA) was placed for respiration and unrestrained feeding recordings respectively, as previously described [11]. The EMG and respiratory airflow parameters were recorded using the MP150 system (BIOPAC Co, CA). The nasal catheter facilitated recording of these parameters during feeding sessions. These recordings were used to determine whether the implanted SONO crystal (Fig 1) had a significant influence on the airflow dynamics of respiration, and/or mastication in the targeted muscles.

Fig 1. Sonocrystal implantation.

Fig 1

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The configuration of 8 ultrasonic SONO crystals (top left color image, scale 10mm) in the tongue base. Empty circles and numbers indicate the location of the crystals. Crystals #1 and #2 were implanted posterior to the two circumvallate papillae underneath the dorsal mucosa, and the #3 and #4 were implanted posterior to crystals #1 and #2 respectively and located in the dorsal area. Crystals #5, #6, #7 and #8 were placed ventrally from crystals #1, #2, #3 and #4, respectively. Each crystal was 20mm apart from each other. The selected SONO crystal pairs for length, width, and thickness are listed. The dotted lines indicate anatomical regions of the tongue. Please note the dorsal surface of the tongue base was intact as all SONO crystals were implanted via submandibular region.

Surgical implantation of SONO crystals and terminal experiment

The minipig was sedated as for the baseline recording. Ringer’s solution was given intravenously, and heated cushions were used for thermoregulation. Eight 2mm B-barbed SONO crystals (Sonometrics Co., Canada) were implanted through a submandibular incision to circumscribe a cubic region in the tongue base as previously described [13]. In brief, the dorsal surface remained intact, and the hyoid bone was the anatomical reference to locating the tongue base ventrally (Fig 1). The SONO crystals were positioned approximately 20mm apart, and their leading wires were sutured to the surrounding soft tissues.

After the crystal implantation, 8 pairs of EMG wire electrodes were inserted as in the baseline. The three sources of signals (SONO, EMG, and airflow) were connected and synchronized with each other via the input/output of the Biopac and Sonometric systems. Respiration was recorded for 2 minutes under sedated sleep (Fig 2B). Then, the minipig was allowed to wake up for unrestrained feeding (Fig 2C) with regular pellet mixed with barium sulfate suspension (Vet-Paque, Jorgensen Laboratories Inc. USA). To verify the jaw movements and the swallowing episodes, a synchronized x-ray videofluoroscopy (30 frames/second, GE Healthcare, OEC 9900 Elite, USA) was simultaneously taken from lateral projections (Fig 2D). Since the animal was fed unrestrainedly, the amount of food was not able to be controlled. However, the amount of ingested and chewed food should have been kept constant as a routine masticatory function. This feature was confirmed with similar bolus sizes for swallowing viewed from synchronized x-ray video fluoroscopy.

Fig 2. Raw tracings of Sonometric recordings.

Fig 2

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Signals obtained during respiration (A and B) and chewing/swallowing (C) alongside simultaneous x-ray fluoroscopy (D) during the feeding session. A: Sample of signals indicating the beginning of inspiration (I, dotted line), the beginning of expiration (E, dotted line), and the total respiratory cycle (box in ADW). Arrows indicate peaks or elongation (RDL, ADW) and valleys or shortening (PVW) when inspiration begins. Underlined ADW indicates the reference pair for timing analysis. B: Crystal pair signaling for length (RVL, LDL, LVL), thickness (RPT), and width (ADW, PVW, PDW). Box and dotted line indicate the respiratory cycle: inspiration (I) and expiration (E). The muscle activity (EMG) of the styloglossus (SG) and middle pharyngeal constrictor (MC) indicate small bursts throughout the cycle. C: Crystal pair signaling for length (LDL), thickness (LAT) and width (ADW, AVW, PVW). The EMG of the middle pharyngeal constrictor (MC), masseter (MA), and digastric (DA) indicate bursts in chewing during jaw opening (O, DA), jaw closing (dotted line/C and bursts in MA, DA) followed by a lower activity during swallowing with increased activity of MC (dotted lines and swallowing burst). The total chewing cycle (box) shows the beginning of jaw opening with elongation (peak) of the reference pair ADW (underline) when DA is active. The opposite occurs in jaw closing. D: Chewing (left) shows the bolus (purple lines) when processed in the back of the mouth. These events including swallowing (right) were observed using videofluoroscopy. The yellow arrows point out the location of the implanted SONO crystals. SP: soft palate. TB: Tongue base. EP: Epiglottis.

The SonoLAB software was used to record the varying distance changes of each crystal pair at a sampling rate of 150 Hz. The inspiratory/expiratory phases of respiration, jaw opening/closing phases of chewing, chewing side, and swallowing episodes in SONO recording were identified using the criteria previously described [11].

Data processing and statistics

Each SONO crystal worked as a signal transmitter and receiver and the distance between each crystal pair could be measured conversely.

For respiration analysis, 15 stable and consecutive cycles were selected from SONO recordings for each animal. (Fig 2A). The values of the peak (upward, distance elongation) or valley (downward, distance shortening) from the baseline were computed and converted to the percentage of the initial distance values. This was to standardize the variations of the tongue sizes and distances between each crystal pair. Due to symmetrical nature of respiratory movements, all the bilateral lengths and thicknesses were combined. In addition, the time sequencing (onset) of changes in each crystal pair during inspiration was converted to a percentage of the total respiratory cycle. The crystal pair #1–2 (anterior dorsal width, ADW) presented the most available and stable wave pattern. Thus, the timing of the ADW was set at the zero-time point to be the reference for other crystal pairs in all time sequence analyses.

For chewing, 10–15 stable and consecutive chewing cycles from each animal were analyzed (Fig 2B). The computing method for distance changes was the same as for respiration. The time sequencing analyses were the same as for respiration but were converted to a percentage of the total chewing cycle length.

Based on the real-time EMG recording using the criteria previously reported [11,12] and videofluoroscopic images, the chewing data was analyzed separately for jaw opening and closing/occlusal phases, and for the ipsilateral and contralateral chewing. An ipsilateral chewing occurred when chewing on the side corresponded to the measured crystal pairs; otherwise, was considered as contralateral chewing. Unlike chewing, swallowing episodes identified by the synchronized videofluoroscopic images occurred sporadically with no consecutive or stereotyped nature. Thus, each swallowing episode was measured independently.

SPSS (version 19.0) was used for statistical analysis. Due to the data not showing symmetrical distribution, the non-parametric Kruskal-Wallis test followed by the pair-wise multiple comparisons (u-test) were used. The significant level was set at p < 0.05.

Results

Compared with the baseline data analyses, no significant differences of the terminal recordings were identified in weight, airflow and EMG, confirming that the implantation of the SONO crystals in the tongue base did not significantly affect respiration and unrestrained feeding.

For respiration, the inspiratory and expiratory phases were determined by the synchronized airflow recordings. For chewing, the jaw opening and closing/occlusal phases and chewing side were determined by the synchronized EMG and fluoroscopic recordings. For swallowing, the episodes were confirmed with synchronized barium fluoroscopic images. Due to the vulnerability of the leading wires of SONO crystals, 8 implanted crystals were not always functioning. Therefore, all measurements were collected from functional crystal pairs only. Sample sizes for animals, analyzed cycles, and available SONO crystal pairs are summarized in Table 1. The results obtained from the EMG, respiratory dynamics, and videofluoroscopic analyses were recently published elsewhere [11,14].

Table 1. Summary sample size of cycles for each pair.

Crystal Pair Total Chewing Cycles Total swallowing episodes Number of pigs Total respiratory cycles Number of pigs
Length RDL 11 2 1 DL 76 3
LDL 13 2 2
RVL 27 3 3 VL 30 1
LVL 14 3 2
Thickness RAT 14 3 2 AT 45 2
LAT 34 1 3
RPT 13 1 2 PT 76 4
LPT 13 1 1
Width ADW 72 5 5 75 5
PDW 14 2 2 30 2
AVW 45 3 3 30 2
PVW 18 1 1 46 3
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Deformational dynamics in respiration

The respiratory cycles were identified as continuous movements from inspiration to expiration including post-expiratory pause (Fig 2A). The average duration of the respiratory cycle was 2.37 ± 0.70 seconds with inspirations of 0.80 ± 0.34 seconds and expirations/pauses of 1.56 ± 099 seconds.

As summarized in Fig 3A the timings for lengths, thicknesses, and posterior widths occurred 10–25% earlier than the reference pair (ADW). Specifically, the timing of the ventral length changes appeared 10–15% earlier than those of dorsal length, widths, and anterior thickness (p < 0.05). In contrast, the timing of the anterior ventral width (AVW) changes was largely behind that of the anterior one (ADW).

Fig 3. Respiration.

Fig 3

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Box-and-whisker plots show (A) time sequences and (B) amplitudes of each selected SONO crystal pair during respiratory cycles. A: % of the starting timing of the deformational change in relation to the anterior dorsal width (ADW, dotted line on time zero). *: significant difference at p < 0.05 by the non-parametric Kruskal-Wallis and pairwise test. B: % of elongation (peaks, upward waves above zero) or shortening (valleys, downward waves below zero) in relation to the initial distance in each SONO crystal pair. *: significant difference at p < 0.05 by the non-parametric Kruskal-Wallis and pairwise test. Refer to Fig 1 for the caption of each selected SONO crystal pair.

During inspiration, peaks were observed in lengths, thicknesses, and anterior widths. The elongation of the ventral length was larger than that dorsally whereas the increase of the anterior thickness was bigger than posteriorly. Similarly, the anterior ventral width elongated more than the dorsal one. In contrast, valleys or shortening were observed in the posterior widths.

Overall, the length, thickness, and anterior widths showed increased between 0.11–2.35%. The largest elongations was in the ventral length compared to those in thickness and anterior widths. Shortenings were between 0.30–0.71% and occurred in the posterior widths (Fig 3B). All this indicates a more elongation/widening/thickening of the anterior and ventral regions with a tendency of shortening/narrowing in the posterior and dorsal regions of the tongue base during inspiratory phases.

Deformational dynamics in chewing

The average duration of the chewing cycle length was 0.55 ± 0.11s. During jaw opening, peaks or elongations were observed in all width dimensions. In contrast, valleys or shortenings were mostly present in lengths and thicknesses except for ventral length and posterior thickness (Fig 4). The beginning of the cycle was detected at the jaw opening phase when the synchronized burst activity from EMG recordings, i.e., activation of anterior digastric muscle, indicated elongation of the reference pair (ADW).

Fig 4. Chewing.

Fig 4

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Box-and-whisker plots show (A) time sequences and (B) amplitudes of each selected SONO crystal pair during chewing cycles. A: % of the starting timing of the deformational change in relation to the anterior dorsal width (ADW, dotted line at time zero). *: significant difference at p < 0.05 by the non-parametric Kruskal-Wallis and pairwise test. B: % of elongation (peaks, upward waves above zero) or shortening (valleys, downward waves below zero) in relation to the initial distance in each SONO crystal pair. *: significant difference at p < 0.05 by the non-parametric Kruskal-Wallis and pairwise test. Refer to Fig 1 for the caption of each selected SONO crystal pair.

Overall, the ipsilateral chewing sides (0.59 ± 0.10s right and 0.57 ± 0.11s left) showed longer durations than their respective contralateral chewing side (0.57 ± 0.13s left and 0.55 ± 0.08s right).

Also, the durations of deformational changes were longer for anterior and posterior thicknesses and ventral length (LAT, RPT, and RVL: 0.60 - 0.65s), and shorter for dorsal length (RDL and LDL, 0.45 – 0.52s) (p < 0.05). No significant differences were detected between the durations of distance elongation and shortening.

The onsets for thicknesses and lengths preceded 2–40% that of the ADW (p < 0.05). Other changes in width occurred between 5–15% after that of the ADW (p < 0.05, Fig 4A). Overall, the peak waves during jaw opening usually showed onsets within the +/- 20% of that of the ADW. In contrast, the valley waves showed onsets within +/- 30% of that of the ADW (p < 0.05). This shows that dimensional elongations happen initially followed by shortenings during the jaw opening phase of chewing.

The ipsilateral and contralateral sides during chewing also showed significant differences. The onsets of the ipsilateral length (12.72 ± 6.13%) and ipsilateral thickness (7.19 ± 9.91%) occurred significantly earlier than those in their contralateral sides (2.06 ± 9.24% length, and 16.71 ± 15.61% thickness, p < 0.05). No significant differences of the onsets were found between the anterior vs. posterior, and dorsal vs. ventral regions for the changes of both lengths and thicknesses.

The range of elongation in width (ADW, PDW, AVW) was significantly larger than that of shortening in length (RDL, LDL, RVL) and thickness (RAT, LAT, p < 0.05). The dorsal lengths showed larger shortenings than those of ventral lengths. The anterior widths increased more than the posterior ones. Similarly, thickness shortened more in the anterior than posterior regions.

Additionally, the dorsal length (RDL) decreased more ipsilaterally than contralaterally (-48.46 ± 4.58% vs -30.68 ± 8.2%) whereas the thicknesses were not significantly different between ipsilateral and contralateral sides (Fig 4B). The right and left ventral lengths and posterior thicknesses showed opposite shape changes regardless of chewing side. It was observed shortening on the right length (5–20%, RVL) and thickening right posterior (5–15%, RPT) with elongation and thinning of the left length and thickness accordingly.

Deformational dynamics in swallowing

As shown in Fig 2B, the swallowing episode started after a brief pause of chewing cycles and occurred in jaw closing.

Given the sporadic and non-consecutive nature of swallowing, no sides were included in the analysis. A total of 10 swallowing episodes from 5 minipigs were analyzed. The average duration of the swallowing episode was 0.69 ± 0.16s. Anterior thickness, dorsal length, and dorsal width showed longer durations. In contrast, ventral width and posterior thickness had shorter durations.

The onset changes of thickness occurred 3–15% earlier than that of the anterior width (ADW). The onsets of length deformation also occurred 3–10% earlier than the ADW. On the other hand, the ventral widths consistently showed 3–15% earlier onsets than those of the dorsal widths. The change of the posterior dorsal width (PDW) occurred later than that of the anterior dorsal width (ADW, Fig 5A).

Fig 5. Swallowing.

Fig 5

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Box-and-whisker plots show (A) time sequences and (B) amplitudes of each selected SONO crystal pair during swallowing episodes. A: % of the starting timing of the deformational change in relation to the anterior dorsal width (ADW, dotted line at time zero). B: % of elongation (peaks, upward waves above zero) or shortening (valleys, downward waves below zero) in relation to the initial distance in each SONO crystal pair. Refer to Fig 1 for the caption of each selected crystal pair.

All distances between SONO crystal pairs elongated (peaks) with the exception of the ventral length (RVL) and posterior thickness (LPT). Although no significant differences were found, larger increases were seen in the dorsal length (RDL) and posterior widths while the largest decrease was observed in the posterior thickness (Fig 5B). This indicates dorsal elongation with posterior widening and thinning in the tongue base during swallowing. The opposite dimensional deformations in these SONO recordings indicated that swallowing movements were not constantly symmetric when it comes to the deformational changes of the tongue base dimensions.

Discussion

Respiration

The analysis in the present study revealed elongation of anterior lenghts, thicknesses, and widths (both dorsal and ventral) along with a minor increase in posterior thickness and simultaneous shortening of posterior widths during inspiration. Therefore, anterior lenghtening, thickening, and widening with posterior shortening of the tongue base feature the shape of the tongue base in inspiration. Some of these findings are similar to those recently reported in young adult minipigs showing lengthening and anterior dorsal widening, but enhanced deformational changes were found in obese minipigs with obstructive sleep apnea (OSA) [13]. In a recent study was analyzed the accumulation of adipose tissue in oropharyngeal structures of young adult minipigs showing tissue predominance in the tongue base and soft palate [15]. Thus, the tongue size and/or adipose tissue infiltration in obese minipigs may contribute to these changes.

Jaw muscles such as the masseter showed a weak but constant activity associated with the inspiratory phase [13]. This might be attributed to the level of muscle contraction to maintain the mandibular position (jaw tone) during inspiration. Therefore, these internal kinematics may contribute to changes of the tongue base during respiration upon volumetric alterations.

Chewing

Dynamic deformations of the tongue base during chewing occurred in all dimensions. From jaw opening, it was predominantly seen in the dorsal length, anterior thickness, and anterior width. The first two showed the largest shortening/thinning and the last one the largest widening. The opposite should have followed during jaw closing/power stroke. As previously reported, the tongue body showed an elongated width of over 33% and a shortened length of 15–16% [10]. In the present study, the tongue base showed a 17% in widening corresponding to half of that in the tongue body. In contrast, a shortened length of 48% in the tongue base indicated a 3-fold larger deformation than that in the tongue body. All this suggests that regional deformations occur in synchrony to fulfill the functional requirements for chewing. Specifically, the larger shortening and widening of the tongue base in jaw opening and following elongation and shortening during jaw closing/occlusal phase may contribute to the formation and transportation of the bolus for swallowing.

The deformational time sequences indicate the order of the changes in each dimension of the tongue base during the chewing. The thickness and ventral length altered 10–30% earlier than the anterior dorsal width, but the changes in other widths occurred slightly later. In the tongue body study, the posterior ventral width was selected as the reference pair. The onsets for thickness and length occurred 20–50% later while the changes in width occurred earlier [10]. All these dimensional deformations of the tongue base and body were reported by using the jaw opening phase as the beginning of the chewing cycle. Consequently, the opposite follows for the jaw closing. Thus, these results are consistent with those of a recent study in pigs reporting increased length of the tongue in jaw closing followed by shortenings in jaw opening [8]. A recent study, also analyzed deformations of the tongue body during chewing reporting transverse (left and right) and sagittal (upwards and downwards) deformations regarless of the jaw position [16]. In the present study, ventral length (RVL and LVL) and posterior thickness (RPT and LPT) showed opposite directions between left and right regarless of the chewing side (Fig 4B). This interesting feature may imply that a left tipping of the tongue base might occur during chewing, resulting in left elongation and posterior right thickening in the tongue base.

All these indicate the same dynamics in both the tongue base and body during chewing. This also suggests that directions and amplitudes of the deformational changes are specific in the tongue base and body. In addition, the time sequences of deformational changes in each dimension remained the same in the tongue base and body during chewing including thicknesses and lengths ahead of the widths. Thus, the tongue body widens first but the tongue base shortens and thins first during chewing. Therefore, it is postulated that deformational changes in the tongue base and body may not be synchronous in a real-time manner likely due to the regional neuromuscular control of the tongue.

Swallowing

In the present study, the swallowing events followed a pause of 1.5-2.0s after multiple consecutive chewing cycles. These events appeared as a transient signal that continued with another pause of variable duration. The data indicated that the propulsive phase of swallowing is related to the dorsal lengthening, posterior widening, anterior thickening, and posterior thinning of the tongue base. These specific deformational dynamics explain the details about the internal kinematics of the tongue base when it retracts to propel the bolus passing through the oropharynx. A recent study in the tongue base of primates and humans found that the activity of the intrinsic muscles and deformational changes are likely related to the movement of the hyoid bone [17,18]. This study further found the increased width and thickness along with sequential changes in the length of the tongue base during the swallowing episodes. These changes were accompanied by the elongation of the palatoglossus, shortening of the genioglossus and the suprahyoid muscles that increased the tongue base volume for retraction. Given the similarity of the masticatory apparatus and function between pigs, primates, and humans [19,20], the present data on the internal kinematic of the tongue base during normal swallowing, provides the database for further studying of the mechanism of swallowing disorders, such as dysphagia.

Conclusion

The deformational dynamics of the tongue base substantially vary in relation to the functional demands by playing major roles in respiration, chewing, and swallowing. The lengthening, thickening, and anterior widening contribute to the shape of the tongue base in the inspiratory phase of respiration. Ipsilateral chewing is characterized by longer durations, shorter lengths, and an increased thickness of the tongue base from the jaw opening to closing as compared with contralateral chewing. The onsets of deformational changes in various dimensions of the tongue base largely differ from those of the tongue body, specifically for the changes in the width and the length. In contrast, larger elongations occurred during swallowing and contributed to the retraction of the tongue base for the bolus propulsion over the epiglottis and towards the esophagus.

Supporting information

S1 File. Raw data on respiration.

(PDF)

pone.0315885.s001.pdf (855.7KB, pdf)
S2 File. Raw data on chewing and swallowing (mastication).

(PDF)

pone.0315885.s002.pdf (1.1MB, pdf)

Data Availability

All relevant data are within the article and its supporting information files.

Funding Statement

This study was supported by grant R01DE028864 from NIH/NIDCR (Z.J.L). The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Decision Letter 0

Ayako Mochizuki

14 Jan 2025

PONE-D-24-55641The Dynamics of Shape Changes in the Tongue Base during Respiration, Chewing and SwallowingPLOS ONE

Dear Dr. Liu,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Your manuscript has been reviewed by two expert reviewers. I would like to inform you that both reviewers have not recommended publication of this manuscript in its present form. Although the manuscript presents interesting new findings, it also contains some drawbacks, as clearly described in their comments.

I would like to encourage you to revise the manuscript extensively according to their comments. You can find their comments at the end of this e-mail.

Please submit your revised manuscript by Feb 28 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

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If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

Kind regards,

Ayako Mochizuki

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at 

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and 

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Thank you for stating the following financial disclosure: 

NIH/NIDCR R01DE028864 to ZJL.  

Please state what role the funders took in the study.  If the funders had no role, please state: ""The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript."" 

If this statement is not correct you must amend it as needed. 

Please include this amended Role of Funder statement in your cover letter; we will change the online submission form on your behalf.

3. Thank you for stating the following in the Acknowledgments Section of your manuscript: 

The authors would like to thank Sydney Honnlee, Sophia Devore, and Elliot Willis of the

University of Washington for their help with animal experiments and data collection. This

study was supported by grant R01DE028864 from NIH/NIDCR (Z.J.L).

We note that you have provided funding information that is not currently declared in your Funding Statement. However, funding information should not appear in the Acknowledgments section or other areas of your manuscript. We will only publish funding information present in the Funding Statement section of the online submission form. 

Please remove any funding-related text from the manuscript and let us know how you would like to update your Funding Statement. Currently, your Funding Statement reads as follows: 

NIH/NIDCR R01DE028864 to ZJL.

Please include your amended statements within your cover letter; we will change the online submission form on your behalf.

4. In the online submission form, you indicated that the datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.

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This policy applies to all data except where public deposition would breach compliance with the protocol approved by your research ethics board. If your data cannot be made publicly available for ethical or legal reasons (e.g., public availability would compromise patient privacy), please explain your reasons on resubmission and your exemption request will be escalated for approval. 

5. Please include your tables as part of your main manuscript and remove the individual files. Please note that supplementary tables (should remain/ be uploaded) as separate ""supporting information"" files.

Additional Editor Comments :

Your paper has been reviewed. The comments of the reviewers are included at the bottom of this letter.

The reviewers have recommended major revisions to your manuscript. Therefore, I invite you to revise and resubmit your manuscript as fast as possible.

Please carefully address the issues raised in the comments.

Kind regards,

Ayako Mochizuki

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: In this study, authors examined the deformational changes of the tongue base during respiration, mastication and swallowing in three dimensions by embedding ultrasonic piezoelectric (SONO) crystals in the tongue base of Yucatan minipigs. It is an interesting research topic, and the data could be important for understanding the mechanisms of respiration and swallowing disorders. However, it is difficult to judge the validity of the data because the quality of the figures overall is low and the explanations in the manuscript are insufficient. In order to improve these points, I think it is necessary to make significant revisions to the manuscript.

Important points

1. It is unclear how the starting timing of the peaks and valleys was determined in the waveform of the lengths, thicknesses and widths at the tongue base. In particular, the peak and valley occur repeatedly in succession during chewing. In such cases, it is important to clearly indicate where the starting timing is.

2. The resolution of the EMG waveform is very low, making it difficult to clearly identify muscle activity. In particular, in the recording of the chewing episode shown in Fig 2B, it is difficult to find muscle activity that coincides with the rhythm of chewing, i.e. the timing of the opening and closing of the jaw. Is this a typical muscle activity of the stylohyoid and masseter muscles while chewing in minipigs? According to the description in Materials and methods, it seems that this study is analyzing the deformation of the tongue base in the jaw opening phase and the jaw closing phase separately, so it is necessary to indicate some kind of indicator that shows the timing of the jaw opening phase and the jaw closing phase. Based on the following description in the manuscript, ‘The beginning of the cycle was detected at the jaw opening phase when the synchronized burst activity from EMG recordings, i.e., activation of the anterior digastric muscle, indicated elongation of the reference pair (ADW). (P12 line 7)’, I propose to show the EMG of the anterior digastric muscle at high resolution.

3. The authors recorded respiration under sedated sleep. I'm concerned that the sedation may affect the movement of the tongue base. Since chewing and swallowing can be recorded while awake, is there a reason why only respiration was recorded under sedated sleep? Please show the validity of recording under sedated sleep.

4. The manuscript contains the following sentence: ‘Sample sizes for animals, analysed cycles, and available SONO crystal pairs are summarised in Table 1.’ However, Table 1 is not included in the manuscript.

5. Fig 4 indicates that, during chewing, the RPT shows the peak wave, while the LPT shows the valley wave. Does this mean that during the jaw opening phase of chewing, regardless of whether it is on the ipsilateral or contralateral side, the thickness of the right posterior region increases, while the thickness of the left posterior region decreases? This also applies to the relationship between RVL and LVL. If the data in Figs 3-5, which are not mentioned in the manuscript, are the combined data of eight animals, then it is thought that there is a certain tendency in the deformational changes in the left and right sides of the tongue base during chewing in minipigs. Describe and discuss the morphological changes on the left and right sides during chewing.

Minor points

1. P6 line7

Is it correct to use a mouth mask to record breathing and a nasal catheter to record chewing? I wonder if the order is the other way round.

2. P11 line15 … valleys or shortening were observed in the posterior widths.

Fig. 2 seems to show that both PVW and PDW have peaks in the inspiratory phase, rather than valleys. Is this sentence in the manuscript correct?

3. P12 line13 … the durations of deformational changes were …

In relation to the starting timing, please specify how authors determined the duration.

4. Fig 1

Add a scale to the top left color image.

5. Fig 2

It is not clear which waveform the black arrow in the EMG in Figure B is pointing to. Please make this clear. In addition, indicate where the jaw opening phase is.

To clarify what is shown in the video fluoroscopy image in Figure C, indicate the names of the main structures in the image.

It is difficult to identify where the implanted SONO crystals are located within the white circle. Please indicate this more clearly.

6. Figs 3-5

The position of the box-and-whisker plots and the axis label are misaligned. IIn addition, the lines showing significant differences are also misaligned, so it is unclear which data is significant. Please arrange them.

Reviewer #2: Liu and colleagues investigated the movement of the tongue base applying ultrasonic piezoelectric (SONO) crystals. The synchronization of EMG and videofluoroscopy provided new insights into the tongue base movement during breathing, chewing and swallowing. The strength of this manuscript primarily is that it conducted movement analysis from new perspective (method) as a functional study of chewing and swallowing. It was very interesting, and I would like to comment from a procedural and clinical perspective.

Minor Comment 1: Please provide more details on the location of the SONO crystal implant. We would like more information, such as the definition of the base of the tongue.

Minor Comment 2: Please indicate whether the animal was trained or fasted before recording.

Minor Comment 3: We believe that it would be better if the definition of swallowing was based not only on SG but also on the activity of the infrahyoid muscles and swallowing apnea.

Minor Comment 4: Please write about the test food for chewing and swallowing recordings. I think that tongue movement changes depending on the amount of food eaten in one bite. What are your thoughts about this?

Minor Comment 5: Was the decision on the chewing side based just only on EMG and videofluoroscopy? Didn't you record both masseter muscles?

Minor Comment 6: Are there any differences in breathing, chewing, and swallowing behaviors between different species? Please describe any chewing or swallowing behaviors unique to mini pigs.

Minor Comment 7: Did you investigate the changes in the shape of the tongue base in response to the flow of the food bolus in the oral cavity?

Minor Comment 8: It is thought that the shape of the tongue base may change depending on the posture of the mini pig during recording, such as when it is facing down or forward. What are your thoughts on this?

Minor Comment 9: Did you investigate the changes in the shape of the tongue base during liquid drinking?

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean? ). If published, this will include your full peer review and any attached files.

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Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy .

Reviewer #1: No

Reviewer #2: Yes:  Kouta Nagoya

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org . Please note that Supporting Information files do not need this step.

PLoS One. 2025 Apr 14;20(4):e0315885. doi: 10.1371/journal.pone.0315885.r003

Author response to Decision Letter 1

29 Jan 2025

Responses to Journal Requirements and Reviewers’ Comments

Journal Requirements

1. When submitting your revision, we need you to address these additional requirements. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

Response: The protocol for Sonocrystal implantation is based on a previous publication from our group. We added the reference accordingly on page 6. The main body and title page were revised following the formatting instructions and templates.

2. Thank you for stating the following financial disclosure:

NIH/NIDCR R01DE028864 to ZJL.

Please state what role the funders took in the study. If the funders had no role, please state: ""The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.""

If this statement is not correct you must amend it as needed.

Please include this amended Role of Funder statement in your cover letter; we will change the online submission form on your behalf.

Response: We provided accurate funding information. The sentence of Funding statement was amended to state that the funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript, and this statement is included in the cover letter.

3. Thank you for stating the following in the Acknowledgments Section of your manuscript:

The authors would like to thank Sydney Honnlee, Sophia Devore, and Elliot Willis of the

University of Washington for their help with animal experiments and data collection. This

study was supported by grant R01DE028864 from NIH/NIDCR (Z.J.L).

We note that you have provided funding information that is not currently declared in your Funding Statement. However, funding information should not appear in the Acknowledgments section or other areas of your manuscript. We will only publish funding information present in the Funding Statement section of the online submission form.

Please remove any funding-related text from the manuscript and let us know how you would like to update your Funding Statement. Currently, your Funding Statement reads as follows:

NIH/NIDCR R01DE028864 to ZJL.

Please include your amended statements within your cover letter; we will change the online submission form on your behalf.

Response: Funding information was removed from Acknowledgements and the Role of Funder Statement was added to the cover letter.

4. In the online submission form, you indicated that the datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.

All PLOS journals now require all data underlying the findings described in their manuscript to be freely available to other researchers, either 1. In a public repository, 2. Within the manuscript itself, or 3. Uploaded as supplementary information.

This policy applies to all data except where public deposition would breach compliance with the protocol approved by your research ethics board. If your data cannot be made publicly available for ethical or legal reasons (e.g., public availability would compromise patient privacy), please explain your reasons for resubmission and your exemption request will be escalated for approval.

Response: Thank you for your clarification. We made available the raw data on respiration, chewing and swallowing as supplementary information.

5. Please include your tables as part of your main manuscript and remove the individual files. Please note that supplementary tables (should remain/ be uploaded) as separate ""supporting information"" files.

Response: Table 1 is now the part of the main body of the manuscript on page 10.

Additional Editor Comments :

Your paper has been reviewed. The comments of the reviewers are included at the bottom of this letter. The reviewers have recommended major revisions to your manuscript. Therefore, I invite you to revise and resubmit your manuscript as fast as possible.

Please carefully address the issues raised in the comments.

Response: We appreciate all comments from the two thorough reviewers. Please find our responses as follows:

Reviewer#1

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Response: We appreciate the feedback. We added multiple editions throughout the manuscript to improve the technical soundness and scientific merits.

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Response: We appreciate this positive feedback.

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Response: We appreciate the feedback. The raw data files obtained from the respiration, chewing and swallowing recordings are available as supporting information (S1 and S2 files).

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Response: We appreciate this positive feedback.

5. Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters).

In this study, authors examined the deformational changes of the tongue base during respiration, mastication and swallowing in three dimensions by embedding ultrasonic piezoelectric (SONO) crystals in the tongue base of Yucatan minipigs. It is an interesting research topic, and the data could be important for understanding the mechanisms of respiration and swallowing disorders. However, it is difficult to judge the validity of the data because the quality of the figures overall is low and the explanations in the manuscript are insufficient. To improve these points, I think it is necessary to make significant revisions to the manuscript.

Response: Many thanks for these comments. We revised all figures for accuracy and quality.

Important points

1. It is unclear how the starting timing of the peaks and valleys was determined in the waveform of the lengths, thicknesses and widths at the tongue base. In particular, the peak and valley occur repeatedly in succession during chewing. In such cases, it is important to clearly indicate where the starting timing is.

Response: Thank you for the comment. Fig. 2A was added to show a sample of raw Sonometric recording which indicates the reference crystal pair (ADW, underlined) and the detection of onsets, peaks, valleys, and durations in all other crystal pairs. These standards were applied for all Sonometric signals on respiration, chewing, and swallowing.

2. The resolution of the EMG waveform is very low, making it difficult to clearly identify muscle activity. In particular, in the recording of the chewing episode shown in Fig 2B, it is difficult to find muscle activity that coincides with the rhythm of chewing, i.e. the timing of the opening and closing of the jaw. Is this typical muscle activity of the stylohyoid and masseter muscles while chewing in minipigs? According to the description in Materials and methods, it seems that this study is analyzing the deformation of the tongue base in the jaw opening phase and the jaw closing phase separately, so it is necessary to indicate some kind of indicator that shows the timing of the jaw opening phase and the jaw closing phase. Based on the following description in the manuscript, ‘The beginning of the cycle was detected at the jaw opening phase when the synchronized burst activity from EMG recordings, i.e., activation of the anterior digastric muscle, indicated elongation of the reference pair (ADW). (P12 line 7)’, I propose to show the EMG of the anterior digastric muscle at high resolution.

Response: We highly appreciate these comments. We improved the EMG signals in Figure 2C. We added the activities of the digastric muscle for the detection of jaw opening, the masseter for jaw closing and power stroke of chewing, and the middle pharyngeal constrictor for the swallowing episode. In addition, we improve the quality of the videofluoroscopy (Figure 2D) to show the sonocrystals and the bolus with more clarity.

3. The authors recorded respiration under sedated sleep. I'm concerned that the sedation may affect the movement of the tongue base. Since chewing and swallowing can be recorded while awake, is there a reason why only respiration was recorded under sedated sleep? Please show the validity of recording under sedated sleep.

Response: We are grateful for this comment. The minipig is active on awaking when not on feeding, thus it would be very difficult to measure the pure respiratory deformations of the tongue base. Therefore, the minipig was placed under sedation for the respiratory recording. Several literatures have indicated that the confounding effect of sedation and anesthesia on respiration has been proven to be minor (Oliven A, Odeh M, Geitini L, Oliven R, Steinfeld U, Schwartz AR, et al. Effect of co-activation of tongue protrusor and retractor muscles on pharyngeal lumen and airflow in sleep apnea patients. J Appl Physiol 2007; Oliven A, O'Hearn DJ, Boudewyns A, Odeh M, De Backer W, van de Heyning P, et al. Upper airway response to electrical stimulation of the genioglossus in obstructive sleep apnea. J Appl Physiol 2003;95(5):2023-9; Mak KH, Wang YT, Cheong TH, Poh SC. The effect of oral midazolam and diazepam on respiration in normal subjects. Eur Respir J 1993;6(1):42-7). On the other hand, we did record the respiratory features during chewing and swallowing, which was published elsewhere (Rosero-Salazar D., Honnlee S., and Liu Z.J.*: Tongue, palatal, hyoid and pharyngeal muscle activity during chewing, swallowing, and respiration. Arch. Oral Biol. 157: e105845, 2024).

4. The manuscript contains the following sentence: ‘Sample sizes for animals, analyzed cycles, and available SONO crystal pairs are summarized in Table 1.’ However, Table 1 is not included in the manuscript.

Response: We appreciate this comment. Table 1 is now included in the manuscript on page 10.

5. Fig 4 indicates that, during chewing, the RPT shows the peak wave, while the LPT shows the valley wave. Does this mean that during the jaw opening phase of chewing, regardless of whether it is on the ipsilateral or contralateral side, the thickness of the right posterior region increases, while the thickness of the left posterior region decreases? This also applies to the relationship between RVL and LVL. If the data in Figs 3-5, which are not mentioned in the manuscript, are the combined data of eight animals, then it is thought that there is a certain tendency in the deformational changes in the left and right sides of the tongue base during chewing in minipigs. Describe and discuss the morphological changes on the left and right sides during chewing.

Response: We appreciate such careful reading of our data. Fig. 4B do show that the ventral left and right lengths (RVL and LVL) and right and left posterior thicknesses had opposite deformational changes regardless of chewing side. These may indicate a left tipping of the tongue base during chewing, thus result in left elongation and posterior right thickening. These explanation was added to the results (p14) and discussion (p17).

Minor points

1. P6 line7

Is it correct to use a mouth mask to record breathing and a nasal catheter to record chewing? I wonder if the order is the other way round.

Response: We appreciate this comment. The mouth mask ensures light sedation using isoflurane 2-3% mixed with oxygen when the data was recorded during respiration. However, chewing and swallowing data was recorded when animal was awake and underwent unrestraint feeding. Clearly, mouth mask could not be used during feeding. Therefore, mouth mask was replaced by a nasal catheter to monitor respiratory airflow during chewing and swallowing. A short explanation about this was added on page 5.

2. P11 line15 … valleys or shortening were observed in the posterior widths.

Fig. 2 seems to show that both PVW and PDW have peaks in the inspiratory phase, rather than valleys. Is this sentence in the manuscript correct?

Response: We appreciate this comment. We improved all figures in terms of accuracy, clarity, and quality. The sentence in the manuscript is correct.

3. P12 line13 … the durations of deformational changes were …

In relation to the starting timing, please specify how authors determined the duration.

Response: Thank you very much for this comment. Figs. 2B and 2C show in boxes the total cycle lengths for respiration (2B) and chewing (2C), The middle-dotted lines indicate the beginning of expiratory (2B) and jaw closing (2C) phases. The time scale is in second.

4. Fig 1

Add a scale to the top left color image.

Response: Thank you very much for this comment. The image was enlarged to show the scale with a total of 10 mm. The note was added to the legend of this figure.

5. Fig 2

It is not clear which waveform the black arrow in the EMG in Figure B is pointing to. Please make this clear. In addition, indicate where the jaw opening phase is.

To clarify what is shown in the video fluoroscopy image in Figure C, indicate the names of the main structures in the image.

It is difficult to identify where the implanted SONO crystals are located within the white circle. Please indicate this more clearly.

Response: Thank you for the feedback. Fig. 2 was improved for all aspects mentioned. Each part of this and other figures were built separately for the better quality.

6. Figs 3-5

The position of the box-and-whisker plots and the axis label are misaligned. In addition, the lines showing significant differences are also misaligned, so it is unclear which data is significant. Please arrange them.

Response: Thank you for the feedback. The arrangements and editions were added accordingly.

Reviewer# 2

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

Response: We appreciate the positive feedback.

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

Response: We appreciate the positive feedback.

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscr

Attachment

Submitted filename: Response to Reviewers.docx

pone.0315885.s004.docx (34.7KB, docx)

Decision Letter 1

Ayako Mochizuki

16 Feb 2025

PONE-D-24-55641R1The Dynamics Shape Changes of the Tongue Base during Respiration, Chewing and SwallowingPLOS ONE

Dear Dr. Liu,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Apr 02 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

  • A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

  • An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

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PLOS ONE

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Comments to the Author

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Reviewer #1: (No Response)

Reviewer #2: All comments have been addressed

**********

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The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

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Reviewer #1: Yes

Reviewer #2: Yes

**********

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Reviewer #1: Yes

Reviewer #2: Yes

**********

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Reviewer #1: Yes

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors responded appropriately to all of my comments. The manuscript has been greatly improved and is now in good condition. I would like to suggest a very minor correction.

1. Fig 2C EMG Scale: Please insert a space between the 500 µV value and the unit.

2. P7 line19 “Respiration was recorded for 2 minutes under sedated sleep (Fig 2A). Then,the minipig was allowed to wake up for unrestrained feeding (Fig 2B) with regular pelletmixed with barium sulfate suspension (Vet-Paque, Jorgensen Laboratories Inc. USA).”

I think (Fig 2A) is a mistake for (Fig 2B), and (Fig 2B) is a mistake for (Fig 2C).

Reviewer #2: (No Response)

**********

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Reviewer #2: No

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PLoS One. 2025 Apr 14;20(4):e0315885. doi: 10.1371/journal.pone.0315885.r005

Author response to Decision Letter 2

20 Feb 2025

Responses to the comments from Editors and Reviewers

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

The reference list was reviewed, and it is complete and correct.

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: All comments have been addressed

Thank you for your positive evaluation.

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Thank you for your positive evaluation.

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Thank you for your positive evaluation.

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Thank you for your positive evaluation.

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Thank you for your positive evaluation.

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors responded appropriately to all of my comments. The manuscript has been greatly improved and is now in good condition. I would like to suggest a very minor correction.

1. Fig 2C EMG Scale: Please insert a space between the 500 µV value and the unit.

A space was made between 500 and µV.

2. P7 line19 “Respiration was recorded for 2 minutes under sedated sleep (Fig 2A). Then,the minipig was allowed to wake up for unrestrained feeding (Fig 2B) with regular pelletmixed with barium sulfate suspension (Vet-Paque, Jorgensen Laboratories Inc. USA).”

I think (Fig 2A) is a mistake for (Fig 2B), and (Fig 2B) is a mistake for (Fig 2C).

Really appreciate the reviewer #1 to indicate these errors. These Figure citations were corrected in page 7.

Attachment

Submitted filename: Responses to the comments from Editors and Reviewers.docx

pone.0315885.s005.docx (23.3KB, docx)

Decision Letter 2

Ayako Mochizuki

5 Mar 2025

The Dynamics Shape Changes of the Tongue Base during Respiration, Chewing and Swallowing

PONE-D-24-55641R2

Dear Dr. Zi-Jun Liu,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Ayako Mochizuki

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

I am glad to say that reviewers and I are satisfied with your manuscript and have decided that it is appropriate to publish it in PLOS ONE. Congratulations on your excellent work!

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: (No Response)

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: (No Response)

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: (No Response)

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: (No Response)

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: (No Response)

Reviewer #2: (No Response)

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy .

Reviewer #1: No

Reviewer #2: Yes:  Kouta Nagoya

**********

Acceptance letter

Ayako Mochizuki

PONE-D-24-55641R2

PLOS ONE

Dear Dr. Liu,

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team.

At this stage, our production department will prepare your paper for publication. This includes ensuring the following:

* All references, tables, and figures are properly cited

* All relevant supporting information is included in the manuscript submission,

* There are no issues that prevent the paper from being properly typeset

If revisions are needed, the production department will contact you directly to resolve them. If no revisions are needed, you will receive an email when the publication date has been set. At this time, we do not offer pre-publication proofs to authors during production of the accepted work. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few weeks to review your paper and let you know the next and final steps.

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Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Ayako Mochizuki

Academic Editor

PLOS ONE

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 File. Raw data on respiration.

    (PDF)

    pone.0315885.s001.pdf (855.7KB, pdf)
    S2 File. Raw data on chewing and swallowing (mastication).

    (PDF)

    pone.0315885.s002.pdf (1.1MB, pdf)
    Attachment

    Submitted filename: Response to Reviewers.docx

    pone.0315885.s004.docx (34.7KB, docx)
    Attachment

    Submitted filename: Responses to the comments from Editors and Reviewers.docx

    pone.0315885.s005.docx (23.3KB, docx)

    Data Availability Statement

    All relevant data are within the article and its supporting information files.

    Articles from PLOS One are provided here courtesy of PLOS

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