Sensory neuromuscular electrical stimulation for dysphagia rehabilitation: A literature review

Abstract

Background

Dysphagia is a common disorder following a cerebrovascular accident. It can cause detrimental effects on patient's quality of life and nutrition intake, especially in older adults. Neuromuscular electrical stimulation has been one of the management strategies for acceleration of the recovery. This review summarises the current evidence on sensory threshold stimulation of the procedure.

Method

This review compiled data from the Internet database PubMed, Cochrane Library and Scopus using combination of MeSH thesaurus: ‘Sensory threshold’, ‘electrical stimulation’, ‘neuromuscular stimulation’, ‘Deglutition’, ‘Dysphagia’. Eleven studies were intergraded into the review.

Results

Most of the studies show significant improvement to the outcomes of sensory neuromuscular electrical stimulation treatment. In many cases, the results of the treatment are comparable or superior to motor threshold stimulation and conventional therapy. However, the study design and parameters of the procedure varied greatly without conclusive standardised guidelines.

Conclusion

The sensory neuromuscular electrical stimulation (SNMES) is a viable treatment option for treating oropharyngeal dysphagia. The most suggested application parameters are an intensity at sensory threshold, a frequency of 80 Hz, an impulse time of 700 μs, a combined total duration of 20 h of stimulation in a 2‐week period, and placing the electrodes in the submental area of the neck. However, further research is necessary to construct a definitive guideline for clinicians.

Sensory neuromuscular electrical stimulation (SNMES) utilizes a low frequency electrical current to treat oropharyngeal dysphagia. However, the parameters of the device and the protocol of the treatment are inconsistent among clinicians. This current review obtained the most suggested setting and summarized the mechanism behind the treatment.

1. INTRODUCTION

Oropharyngeal dysphagia is a disorder categorised by the impaired function of the apparatus responsible for swallowing. ¹ It is one of the most common complications among post‐stroke patients. Occurring in 64% to 78% of patients recovering from a stroke, ² this disorder is reported to be a major cause of malnutrition, dehydration, aspiration and respiratory complications. Usually, the conditions gradually improve during the first few weeks after the stroke, but 50% of the patient develop prolonged dysfunctionality lasting several months. ³ In severe cases, during the first year of the symptoms, up to 37%–78% of the patients suffer from aspiration pneumonia, ² , ³ an infection that can lead to an increased mortality rate. ⁴

Conventional management strategies for dysphagia involve strengthening exercise, posture modification and diet replacement. Another approach with evidence of effectiveness is neuromuscular electrical stimulation (NMES). ⁵ , ⁶ The treatment utilises electrical current‐applied transcutaneous to the submandibular area to stimulate muscles and nerve fibres. ⁷ , ⁸ Two approaches to NMES have been introduced. First, ‘Motor neuromuscular electrical stimulation’ which aims to evoke contraction from muscles responsible for swallowing, resulting in a reduction in pharyngeal transit time, swallow response time and aspiration rate. It also increases laryngeal elevation, vocal fold closure, swallowing frequency and improves airway protection. ⁹ , ¹⁰ In order to evoke muscle contraction, a relatively high frequency of voltage had to be applied to the area. On the other hand, ‘Sensory neuromuscular electrical stimulation (SNMES)’ utilises a lower frequency only to stimulate the afferent sensory neural pathway and establish a long‐lasting cortical excitability improvement, enabling the motor functions to be activated more easily. ¹¹ , ¹² , ¹³

During the past decade, NMES has been studied and utilised extensively in clinical practice, but the method and protocol of the treatment are far from being standardised, ¹⁴ especially SNMES. A major concern with the current practices is that the electrical intensity used by each clinician varies greatly. ¹⁵ A definitive consensus needs to be established to guide clinicians to achieve optimal treatment success. In this article review of published literature, we summarise the current concept and evidence of SNMES treatment on dysphagic patients. Additionally, we examine the significance of different treatment specifications and discuss the disputable mechanism behind SNMES.

2. METHODS

2.1. Literature search strategies

A combination of manual search and electronic search utilising Internet research database PubMed, Cochrane Library and Scopus were conducted. MeSH thesaurus used as free terms for search are the following: Sensory threshold, electrical stimulation, neuromuscular stimulation, Deglutition, Dysphagia. The search and selection process were concluded on (4st February 2022).

The result of the search showed 81 articles which matched the search keys. A manual search was also conducted, yielding a total of 22 articles. Abstracts and titles of each article were screened. Review articles, non‐clinical experiments, pilots and unrelated titles were excluded. A complete read of the remaining 24 articles was conducted. Eleven articles were selected for inclusion in present article review. The inclusion criteria are articles published after the year 2000, articles in which patients were treated either with SNMES or SNMES with traditional therapy and articles which revealed device parameters used on experiments. Articles excluded are articles with animal experiments, articles in which the stimulation method is percutaneous or used motor threshold stimulation intensity and articles in which outcome measurements are incomparable with other articles, as shown in Figure 1.

FIGURE 1.

Chart detailing the article selection process

3. RESULTS

3.1. Electrode placement location

Depending on the articles, the locations of the electrodes are mentioned either as a general area on the skin surface or specific muscles the authors intended to stimulate as indicated in Table 1. The placement of the electrodes varied between articles, but the majority of the authors targeted areas around swallowing muscles (omohyoid, sternohyoid, sternothyroid, thyroid muscles). All the articles used the anterior surface of the neck as the placement site. ¹⁷ , ¹⁸ , ¹⁹ , ²⁰ , ²¹ , ²² , ²³ , ²⁴ , ²⁵ Some authors precisely specified the location with definition and visual images, ¹⁷ , ²¹ , ²³ , ²⁵ while others did not pinpoint the exact location. ¹⁸ , ¹⁹ , ²⁰ , ²² , ²⁴ Three of the articles placed the electrodes in the submental area. ¹⁸ , ²³ , ²⁴ Shimizu et al.19 investigated the difference in surface electrode placement pattern in the submental area, revealing that placing the devices at just left and right of the midline between the mandibular tip and the hyoid centre yielded most significant anterior hyoid movement than the more distal positions on the same horizontal plane or four electrodes of the previous two placement locations combined. Beom et al.20 compared the result of placing four electrodes at the suprahyoid area and placing two at the submental area together with one at the suprahyoid area and one at the infrahyoid area. The result showed no significant difference between the application sites. Lim et al.16 also used both submental and infrahyoid regions for the stimulation sites of four electrodes. Rofes et al.18 described in the protocol as a thyroid area, while Xia et al. ¹⁷ did not give a specific location. Examples of the electrodes placement locations can be found in Figure 2.

TABLE 1.

Articles included in this review

Author	Subjects	Stimulation site	Device	Frequency	Impulse ime	Session	Outcome measurement
Lim et al. 2009 16	28 Dysphagic patients (mean = 67.8 years)	Between the anterior belly of the digastric muscle and hyoid bone, Between the thyroid cartilage and cricoid cartilage	VitalStim®	Not described	Not described	1 h 5 Session/week 4 weeks (20 Sessions ‐ 20 h)	SFS, PAS, PTT
Gallas et al. 2010 13	11 post‐stroke dysphagic patients (67 ± 11 years)	Submentally in front of the mylohyoid muscles	Biopac	80 Hz	Not described	1 h/session 1 session/day 5 days (5 Sessions ‐ 5 h)	SRT, PAS, PTT, OTT, LCD, Swallowing questionnaire
Xia et al. 2011 17	120 post‐stroke dysphagic patient (40–80 years)	Swallowing muscles	VitalStim®	80 Hz	700 μs	30 min/session 2 session/day 4 weeks (20 days) (40 Sessios ‐ 20 h)	SWAL‐QOL, SSA, VFSS, sEMG
Rofes et al. 2013 18	20 post‐stroke patients (74.95 ± 2.18)	Thyroid area	VitalStim®	80 Hz	700 μs	1 h/day 1session/day 2 weeks (10 days) (10 Sessios ‐ 10 h)	EAT‐10, SSQ, PAS, Laryngeal vestibule and upper oesophageal sphincter closing/opening time
Shimizu at el. 2014 19	5 healthy volunteers (24.2 ± 1.3 years)	Type 1: Suprahyoid medial Type 2: Suprahyoid distal Type 3: Suprahyoid pervasive	ES‐510	30 Hz	Not described	Instant (1 session)	Hyoid movement
Beom et al. 2015 20	96 Disphagic patients	Group A: 2 midpoints between the mandibular angle and chin +2 midpoint between the chin and the edge of the hyoid bone Group B: 2 points Above the hyoid bone +1 point above the thyroid cartilage +1 point below the thyroid cartilage.	Stimplus® VitalStim®	60 Hz for Stimplus® 80 Hz for VitalStim®	500 μs for Stimplus® 700 μs for VitalStim®	30 min/session 11.2 ± 3.4 sessions for Stimplus® 11.9 ± 3.4 sessions for VitalStim® (Approx. 12 Sessios ‐ 6 h)	FDS, SFS, PAS
Zhang et al. 2016 21	82 medullary infarction ‐ dysphagia patients (62.2 ± 9.2 years)	Submental region, occipital area	vocaSTIM‐Master	25 Hz	750 ms	20 min/session 2 session/day 4 weeks (20 days) (40 Sessios ‐ 13.33 h)	SWAL‐QOL, SSA
Ortega O et al. 2016 22	38 dysphagic patients (>70 years)	Thyroid area	VitalStim®	80 Hz	700 μs	1 h/session 1 session/day 2 weeks (10 days) (10 sessions ‐ 10 h)	EAT‐10, PAS, SRT, Hyoid Movement
Maeda et al. 2017 23	43 dysphagia patients (82.7 ± 8.0)	Edge of the thyroid cartilage, 4 cm from the ipsilateral, and along the mandible.	Gentle Stim®	50 Hz	Not described	15‐min/session 2 session/day 2 weeks (10 days) (20 Sessios ‐ 5 h)	PAS, CLT, FOIS, Nutrition Oral Intake
Umay et al. 2020 24	102 cerebral palsy children with dysphagia (49.73 ± 12.30 months)	Ramus of the mandible and bell of the mandible	Intelect advanced‐Chattanooga	Not described	Not described	30 min/session 1 session/day 4 weeks (20 days) (20 Sessios ‐ 10 h)	FEES, Pedi‐Eat‐10
Costa D et al. 2020 25	10 dysphagic patients (median = 58 years)	Mylohyoid muscle and Thyrohyoid muscles	VitalStim®	80 Hz	700 μs	Instant (1 session)	PTT, OTT, DOSS, Eisenhuber scale

Abbreviations: CLT, Cough latency time; DOSS, Dysphagia Outcome and Severity Scale; EAT‐10, Eating Assessment Tool; FEES, Flexible fibreoptic endoscopic evaluation of swallowing; FDS, Functional Dysphagia Scale; FOIS, Functional oral intake scale; LCD, Laryngeal closure duration; OTT, Oral transit time; Pedi‐Eat‐10, Paediatric Eating Assessment Tool; PAS, Penetration–aspiration scales; PTT, Pharyngeal transit time; sEMG, Surface Electromyography; SFS, Swallow function scores; SRT, Swallow Response Time; SSA, Swallowing Assessment; SWAL‐QOL, Swallowing‐related quality of life; SSQ, Sydney Swallow Questionnaire; VFSS, Videofluoroscopic Swallowing Study.

FIGURE 2.

Illustration of electrode placements; (1) Gallas et al. 2010, (2) Zhang et al. 2016, (3) Beom et al. 2015

3.2. Intervention and stimulus durations

Regarding the intervention, all the results showed a positive response to the stimulation. However, the result could not be compared because of the difference in outcome measurements, protocols and causes of dysphagia of subjects. Each session length was between 15 and 60 min with the frequency of one session per day ¹³ , ¹⁶ , ¹⁸ , ²⁰ , ²² , ²⁴ or two sessions per day. ¹⁷ , ²¹ , ²³ In most articles, the intervention duration from start to finish was 4 weeks. ¹³ , ¹⁷ , ²¹ , ²⁴ The others chose a shorter period of two weeks ¹⁸ , ²² , ²³ or lower. Gallas’ intervention ¹³ was 5 days, whereas Beom et al.20 varied the duration between participants. Calculating from the length of each session, frequency of intervention and duration of the entire treatment, participants experienced a total of 20 h of stimulation in three of the articles, ¹⁶ , ¹⁷ 33 h in Zhang's intervention, ²¹ 10 h for Rofes’ and Ortega's, ¹⁸ , ²² and less than 10 h in two other articles. ¹³ , ²⁰ Despite the variety of treatment duration, every article showed positive results except for Costa et al.25 whose results were measured after one stimulation session.

3.3. Device parameters

Intelect VitalStim device (Chattanooga Group, Hixson, TN) was used in most cases as the stimulation device. ¹⁶ , ¹⁷ , ¹⁸ , ²⁰ , ²² , ²⁵ Other devices used were Stimplus® (Cyber‐medic Corp., Iksan, Republic of Korea), ²⁰ vocaSTIM‐Master (Physiomed Elektromedizin), ²¹ Galvanic stimulation (Intelect Advanced‐Chattanooga, UK), ²⁴ and 0–150 V; Biopac, ¹³ Gentle Stim® (J Craft, Osaka, Japan). ²³

The parameter setting of the device in each intervention included frequency, impulse time and intensity. Although some articles did not include these parameters in the research method, ²⁴ the frequency most used was 80 Hz. ¹³ , ¹⁷ , ¹⁸ , ²² , ²⁵ Lowered frequencies were applied in the others. ¹⁹ , ²¹ , ²³ However, the result also showed significantly positive effectiveness. One article ²⁰ utilised interventions with 80 and 60 Hz frequency which did not show a significant difference, although each intervention's device, impulse time and electrode position also diverged. The most used impulse time was 700 μs. ¹⁷ , ¹⁸ , ²⁰ , ²² , ²⁵ Other articles did not mention this parameter, except Zhang et al.21 which used 750 μs. The intensity of SNMES cannot be described as a single value for every participant as each individual's threshold is different. It is determined by gradually increasing the intensity until the patient felt a ‘Tingling’ sensation without muscle contraction. This process of establishing the participant's sensory threshold is done before each treatment session.

3.4. Effects of sensory electrical stimulation

Three of the articles compared the efficacy of SNMES to both the motor approach and conventional therapy. ¹⁷ , ¹⁸ , ²¹ The results suggested that the sensory approach yielded similar outcomes to the motor approach, in which the improvements in patient swallowing ability and safety exceed conventional therapy. Patients responded positively to swallowing‐related quality of life (SWAL‐QOL) ¹⁷ , ²¹  and swallow questionnaires, ¹³ , ¹⁸ but patients who only received SNMES did not present significantly different results from those who received only conventional therapy. ²¹ However, combining traditional swallow training with stimulation at the sensory level, significantly improved both patient questionnaire scores and other assessment values. ¹⁷ , ²¹ In Xia's article, ¹⁷ the sensory stimulation approach combined with conventional therapy even yielded greater improvement over its motor counterpart.

Regarding other parameters used for assessment of pre‐ and post‐intervention, the safety of swallow was found to be improved in both treatment intensities as Rofes ¹⁸ reported a reduction in oral residue in both approaches. However, the penetration–aspiration scales (PAS) only significantly reduced in the sensory group. Another study compared the safety of swallowing between the SNMES group and sham group, which the result showed a significant improvement of cough latency time (CLT) in patients undertaken SNMES. ²³ An early study ¹³ showed improved swallowing coordination from patients with sensory threshold intensity stimulation, yet the pharyngeal transit time (PTT) and Oral transit time (OTT) did not change. Rofes ¹⁸ assessed the function of swallowing organs by videofluoroscopy and reported decreases in laryngeal vestibule opening‐closing time; however, upper oesophageal sphincter opening time did not reduce. To summarise definite outcome of sensory neuromuscular electrical stimulation, further studies on long‐term outcome, patient selection and variations in technique is needed. ⁸ , ²⁶

3.5. Mechanism of sensory electrical stimulation

Swallowing is a complex process involving multiple cortical and subcortical neural pathways. In order for it to progress appropriately and smoothly, the coordination between the central nervous system and cranial nerves, including afferent and efferent pathways, must be achieved. ⁸ , ²⁷ The beginning of the sequence stems from the cerebral cortex in both hemispheres. ⁸ , ²⁸ , ²⁹ The descending motor inputs are received by an interneural network located in the lower brain stem called the central pattern generator (CPG) and distributed to the appropriate motoneuronal pools which initiate harmonious muscle movements. ⁸ , ¹² , ²⁷ , ²⁸

Studies ²⁹ , ³⁰ , ³¹ in this area reported that sensory inputs also play an essential role in this motor sequence apart from the motor inputs. Sulica ²⁹ indicated significant increased pharyngeal residual, laryngeal penetration and a higher incidence of tracheal aspiration in laryngeal anaesthetised patients. Decreased swallowing speed and volume are also shown in Teismann's experiment ³⁰ with anaesthetised oropharynx healthy patients. The impeded function was due to the lack of sensory feedback mechanism required in the deglutition process. Sensory information of the food being ingested normally travels from temperature, pressure and chemical receptors in the oropharynx, larynx and oesophagus via the trigeminal nerve (V), the glossopharyngeal nerve (IX) and the vagus nerve (X) to the brain stem where the CPG is located. Thereafter, the CPG adjusts the motor sequence in order to respond to the bolus characteristics, thus forming a feedback mechanism. ⁸ , ²⁷ , ³² Many works of literatures ¹¹ , ¹³ , ²⁷ , ³³ , ³⁴ have reported that repetitive sensory input could induce long‐term activity modification to the central programme.

In recent years, there has been increasing interest in this concept for a new strategy for dysphagia rehabilitation. In case of a stroke, the patient will undergo a reorganisation of cortical motor representations of the unaffected hemisphere to compensate for the motor deficit in the affected side, ³⁵ ultimately resulting in a full or partial recovery. During this period, interventions that promote neuroplasticity which is an adaptation to the neural network function resulting from varied sensory experiences or stimuli, ³⁶ could enhance the process and the result. Cortical plasticity is influenced greatly by neuromodulators, namely acetylcholine and norepinephrine, originating from the basal forebrain and the locus coeruleus of the brain stem. By manipulating the release of either of these substances, plasticity in the motor cortex can be enhanced. ³⁷ , ³⁸ , ³⁹ This release regulation mainly contributed to the vagus nerve which its fibres synapse to the neurons within the nucleus tractus solitarius in the brain stem, which afterwards transfers to the basal forebrain and the locus coeruleus. ⁴⁰ , ⁴¹ SNMES applied to the front of the neck at the submandibular area targets sensory receptors which majority of their afferent fibres project to the vagus nerve, thus prompting acetylcholine and norepinephrine release.

SNMES lowers the swallowing threshold for patients with impaired deglutition function. In addition, it enables the initiation of the sequence with less latency time and improved coordination of motor activity of muscles. ¹² Early study has proved that SNMES can alter the central nervous system by improving the motor cortex excitability and increasing representation for the pharynx ¹¹ as a result of neuroplasticity. This result is consistent with the later experiments, ³⁴ which involved monitoring the cerebral cortex activity with MRI after treating subjects with SNMES at different intensities, resulting in faster initiation of each swallowing and reducing the frequency of aspiration.

Later studies ¹³ , ¹⁶ , ¹⁸ , ¹⁹ , ²⁰ , ²³ , ⁴² utilising this approach presented significant improvement to the outcomes on post‐stroke dysphagic patients, mainly performed when coupled with conventional swallow therapy. ¹⁷ , ²¹ Therefore, SNMES could produce a similar effect to motor electrical stimulation treatment except for the absence of actual muscle movement, eliminating the risk of aspiration that often occurs during treatment. This advantage of SNMES can be useful for treating patients with peripheral sensation impairment.

It is important to note that a major limitation of the current studies regarding this topic is an inconsistency of the procedure. The intensity of electrical current, the location of electrodes and the duration of the intervention vary between different studies. ⁸ However, despite its controversy, SNMES shows promising potential for a rehabilitation strategy for dysphagic patients. More research is needed to attain a clear finding of the optimum technique to be standardised.

4. DISCUSSION

The current article review aims to examine the parameters of treatment protocol used in previous SNMES studies and accumulate evidence of its mechanism. Electrical stimulation at sensory threshold was first introduced as a treatment for oropharyngeal dysphagia by Hamdy S. in 1998, who suggested that modulating sensory input can lead to a long‐term increase in motor cortex excitability in the pharyngeal area. ¹¹ This discovery led to numerous attempts to establish SNMES as a valid treatment option for dysphagic patients.

The strategy to enhance motor function by using sensory electrical stimulation has been applied to other body regions with a mostly positive degree of success. Upper limb function rehabilitation after stroke showed a significant favourable effect of SNMES, ⁴³ especially on dorsiflexion force, ¹⁴ and some studies showed a positive effect on pinch force of the subjects. ⁴⁴ , ⁴⁵ This effect could last as long as 30 days after a single treatment session and leave a long‐lasting effect if coupled with active motor training. ⁴³ SNMES is also effective in managing lower limb impairments and improving postural regulation in adults and elders. ⁴⁶ However, this only includes basic static balance tasks, not athletic performances. The adverse effect after SNMES treatments was minimal in most cases. ¹⁴ , ⁴³ , ⁴⁶ To not invoke muscle contraction but only cause paresthesia in extremities therapies, the frequency of pulse used for stimulation is 10 Hz with a short pulse duration of 1 ms and 2 h of treatment for each session. These are the optimum parameters to improve cortical motor excitability both in animal models and in stroke patients. ⁴³ After 2 weeks of both SNMES and motor training, magnetoencephalography revealed reduced intrinsic synchronicity of the affected precentral gyrus which indicates improved motor function. ⁴⁷ The efficiency of SNMES has also been compared with transcranial magnetic stimulation to the unaffected side of hemisphere of post‐stroke patients. Both outcomes were more favourable than those of the control group, according to the results. However, high frequency transcranial magnetic stimulation produced greater results in swallowing disturbance questionnaire and PAS. ⁴⁸

The working mechanism behind SNMES has been a controversial subject of the treatment since its introduction, mainly because of a limited number of related studies. Sulica ²⁹ and Teismann ³⁰ demonstrated that the absence of sensory input from the oropharyngeal region resulted in difficulty swallowing, suggesting the involvement of its influence in the process. These findings, combined with a considerable volume of literature, proposed a possible mechanism of SNMES. Studies found that acetylcholine and norepinephrine play an essential part in enhancing the neuroplasticity of the motor cortex. ³⁷ , ³⁸ , ³⁹ Stimulating the vagus nerve or the area around it promotes the release of these neuromodulators. Therefore, it improves the recovery of deglutition function. ³⁵

Despite its clinical success in previous studies, there has been no consensus on the protocol for applying the SNMES. Its parameters and device settings change according to each clinician's intuition. The electrical current's frequency and impulse time differentiate among the studies, but a comparison study showed no significant difference between different frequencies, ²⁰ and there has not been a clear significant result that indicates that different impulse time will affect the outcome. The most used frequency is 80 Hz ¹³ , ¹⁶ , ¹⁷ , ¹⁸ , ²² , ²⁵ and the most used impulse time is 700 μs. ¹⁷ , ¹⁸ , ²⁰ , ²² , ²⁵ Another vastly diverged variable is the placement of the electrodes. They are generally placed in the submental and thyroid area of the neck, but the exact locations differentiate from one another. ¹⁷ , ¹⁸ , ¹⁹ , ²⁰ , ²¹ , ²² , ²³ , ²⁴ , ²⁵

The limitation of this current review was that the number of currently available studies related to SNMES was limited. The parameter and study design set by clinicians were inconsistent. It was difficult to construct a clear comparison of the results, especially when the outcome and evaluation method were disparate. Nevertheless, SNMES presents positive outcomes among all the studies, reaching similar results as electrical stimulation using motor threshold electrical intensity. ¹⁸ , ¹⁹ , ²¹ , ²⁴ The patient experienced improved quality of life and clinical assessment compared to patients who only received traditional swallowing therapy. Interestingly, by combining both SNMES and traditional therapy, the treatment effects are enhanced. ¹⁷ , ²¹

5. CONCLUSION

The SNMES is a viable treatment option for treating oropharyngeal dysphagia. The most suggested application parameters are an intensity at sensory threshold, a frequency of 80 Hz, an impulse time of 700 μs, a combined total duration of 20 h of stimulation in a 2‐week period and placing the electrodes in the submental area of the neck. Lastly, a combination of SNMES and traditional swallowing therapy including muscle training and exercises yields improved results. However, further studies of application parameters, patient selection and techniques should be done to establish a definite methodology for the most appropriate treatment protocol.

AUTHOR CONTRIBUTIONS

All co‐authors took part in the conceptualisation and preparation of this manuscript. Itt Assoratgoon and Naru Shiraishi drafted the initial manuscript, designed the data collection instruments, collected data, and conducted the initial analyses. Ryo Tagaino, Toru Ogawa and Keiichi Sasaki critically reviewed the manuscript. All co‐authors revised the manuscript.

ACKNOWLEDGEMENTS

This study was partly supported by Grants‐in‐Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (Tokyo, Japan; grant numbers: K22K100920).

CONFLICT OF INTEREST

The authors declare that they have no competing financial interests or personal relationships that could have influenced the work reported in this paper.

PEER REVIEW

The peer review history for this article is available at https://publons.com/publon/10.1111/joor.13391.

Assoratgoon I, Shiraishi N, Tagaino R, Ogawa T, Sasaki K. Sensory neuromuscular electrical stimulation for dysphagia rehabilitation: A literature review. J Oral Rehabil. 2023;50:157‐164. doi: 10.1111/joor.13391

DATA AVAILABILITY STATEMENT

Data sharing is not applicable to this article as no new data were created or analysed in this study.