Association between Tinnitus and Auditory Middle Latency Response: An Exploratory Study

Abstract

Tinnitus is a concerning condition that affects most adults worldwide, with a prevalence of 6.7%. Theories of tinnitus have explained that an increase in spontaneous neural activity at the level of the thalamus could induce tinnitus. There are no standardized objective tests for tinnitus assessment because of its multifaceted nature. Hence, the current study aimed to explore the effect of Tinnitus on Latency and Amplitude of the Auditory Middle Latency Response in Audiological Attendees. The study recruited 50 individuals (25 normals and 25 individuals with tinnitus) who underwent audiological evaluations like Pure tone audiometry, immittance, pitch and loudness matching, THI and middle latency response. The IHS program was used to record MLR, which was obtained using tone burst stimuli of 500 Hz, 1 KHz, 2 KHz, and 4 KHz at a rate of 7.1/s with a constant duration of 5 ms, for a total of 1500 sweeps. As a covariate, pure tone thresholds were one of the variabilities that were addressed by ANCOVA. The amplitude of the Pa component varied significantly between the tinnitus and control groups, according to the MLR data and no other components of MLR reached that significance. Furthermore, there was no discernible variation in the latency or amplitude of MLR among any of the other components. The latency of the waveforms increased as the stimulus frequency increased. Karl Pearson correlation coefficient showed no significant correlation between THI scores and any of the outcome measures except for Pa amplitude. As the Pa component of MLR showed maximum changes between controls and individuals with tinnitus, the Pa component could be considered a potential tool for identifying neurophysiological changes related to tinnitus.

1. Introduction

Tinnitus is the sense of sound that the individual will experience in the absence of external sounds (Baguley et al., 2013). Tinnitus can be classified as either objective, where the examiner can hear the tinnitus, or subjective, where only the affected person will experience the sound (Baguley et al., 2013; Esmaili and Renton, 2018). Furthermore, tinnitus is divided into primary and secondary based on the causes; primary tinnitus is associated with sensorineural hearing loss and lacks an identifiable cause and is more often presented as subjective in nature (Danesh et al., 2024). Secondary tinnitus is often associated with an identifiable underlying condition, such as ear infections, cardiovascular issues, diabetes or myofascial dysfunction (Mavrogeni et al., 2022; Molnár et al., 2025). The prevalence of tinnitus in the entire world ranged from 4% to 37%, and in other reports, the global prevalence was between 10% to 15% (Manchaiah et al., 2018; Jarach et al 2022). The epidemiological data suggests, nearly 6.7% of middle-aged adults deal with tinnitus in India (Langguth et al., 2013; Aryal et al., 2022). As the tinnitus sensation becomes worse, it affects the individual's quality of life, sleep disturbances, and annoyances, and it becomes more bothersome. Additionally, there is substantial evidence indicating a strong correlation between tinnitus and mental health issues, particularly depression and anxiety i.e., patients with more severe tinnitus shows higher levels of depression and anxiety (Molnár et al., 2025). According to ICF, the effects of tinnitus can be of two kinds, that is, the primary and secondary impacts. The primary impact of tinnitus includes limitations in Body functions such as mental functions, sleep disturbances, or sensory function/pain, and Activity limitations include attention/cognitive functional or communicative limitations (Nondahl et al., 2007; Marín and Soto, 2022). The secondary impact of tinnitus includes environmental factors such as intensity and quality of the sounds in the surroundings, and contextual factors, and Contextual factors such as comorbid conditions that cause tinnitus to be severe (Manchaiah et al., 2022).

At present there is no standard objective test protocol for assessing tinnitus, hence the tinnitus evaluation procedure relies on subjective tests like collecting history, pure tone audiometry, tinnitus (pitch and loudness) matching, and questionnaires, which assess the quality of life and severity of tinnitus (Tang et al., 2019). Recent fMRI studies have shown a reduction in neural inhibition in the areas of thalamocortical pathways, hence creating more neural noise (Berlot et al., 2020). Significant inhibition was also found in the thalamic gating process through fMRI studies and suggested that activation of the thalamus plays an important role in therapy (Jimoh et al., 2023). Numerous neuroimaging tests like CT, MRI, and fMRI have been performed in studies to study tinnitus. Recently, fMRI studies have shown modifications in the auditory pathways, including the limbic system, attention system, default mode network, and a few areas of cognition (memory, emotion, attention, and control) (Chen et al., 2020). Another study which utilized the carotid-vertebral ultrasonography found out that individuals with intimal hyperplasia (the thickening of the inner lining of a blood vessel) had shown elevated pure tone thresholds and ultimately increased perception in tinnitus intensity(Molnár et al., 2025). Additionally, perception, persistence, and severity of the tinnitus can cause these alterations in functional connectivity and neural activity (Gentil et al., 2019). Additionally, fMRI uses Blood Oxygen Level Dependent (BOLD) method, which is an indirect measure of neural activity, which has lower temporal resolution compared to that of electrophysiological tests (Heugel, 2020). However, the clinical utility of such techniques is masked by several factors like invasiveness and cost-effectiveness.

Auditory Evoked Potentials (AEP) are the electrical signals that are produced with the auditory stimulus, and these are useful in assessing neural integrity from the cochlea to the cortex. Auditory Middle Latency Response (AMLR) is an electrophysiological test that is used to assess the auditory system at 10 to 80 milliseconds following the auditory stimulus. Studies on AMLR have revealed that it is sensitive to finding responses at the level of the thalamus and can be elicited by acoustic and electrical stimulation. Components of MLR, like Na (negative peak) and Pa (positive peak) are said to be generated by subcortical and cortical structures, respectively, around the region of the thalamus. Few studies have tried to explore the pathophysiology of tinnitus using MLR. However, none of the studies found significant differences between controls and the test group (tinnitus) (Theodoroff et al., 2011; Jacxsens et al., 2022). However, these study findings can be varied due to methodological differences like protocol used for the test, electrode channels, stimulus, type, and severity of tinnitus. Majority of previous studies have used click stimulus to elicit MLR in tinnitus individuals, which may not be the right stimulus as perception of tinnitus is frequency specific. This study employed the use of tone burst stimuli for recording the AMLR, as tinnitus is perceived as having different pitches in each individual. Hence, using click stimuli alone does not give us an idea about frequency-specific effects in the auditory pathway. Moreover, we included individuals with sensorineural hearing loss in the study, as hearing loss and tinnitus often co-occur as symptoms of hearing loss. Hence, the unitary and the combined effect of hearing loss and tinnitus on subcortical and cortical structures could be better understood. Also, studies have elicited MLR in individuals with normal hearing but exploring MLR in individuals with tinnitus and hearing loss may be interesting as tinnitus is usually associated with hearing loss. Hence, we hypothesized that individuals with tinnitus would show significant differences in the latency and/or amplitude of the AMLR components, particularly the Pa wave, compared to controls. Therefore, the study aimed to study the effect of Tinnitus on Latency and Amplitude on Auditory Middle Latency Response in Audiological Attendees.

2. Methods

2.1. Subjects

A total of 25 controls (without tinnitus) and 25 individuals with tinnitus in the age range of 20 to 55 years were considered for this study. All the participants were selected through a convenient sampling method which followed cross sectional study design. Sample size was determined using G*Power (v3.19.7) with 95% confidence and 80% power, and descriptive statistics used to derive the sample size were taken from study by (dos Santos Filha et al., 2015). For controls, only Right-Handed individuals were considered as estimated by the Edinburgh Handedness Inventory, with normal Pure tone thresholds (less than 25 dB HL), with no complaints of middle ear infections, and THI scores less than 16. That means, all the participants who were assessed with THI had shown a normal score of 0 (No handicap), which indicated that the control group did not have tinnitus at a pathological level. For the Tinnitus group, right handers, Pure tone thresholds less than 40 dB HL, no complaints of middle ear infections, and THI scores greater than 16 were included in the study. All the participants had primary tinnitus complaints and the study population consisted of individuals with both acute and chronic cases of tinnitus. Participants who had hearing loss greater than 40 dB HL, complaints of Middle ear infections, and Left-handed individuals were excluded from the study. Before the commencement of the testing, written consent was obtained from all the participants of the study. This study was approved by Institutional Ethics Committee, Kasturba Medical College, Mangalore, MAHE, Manipal (approval number: IEC KMC MLR 04/2024/210; Date of approval: 18/04/2024).

2.2. Test Procedure

A thorough case history was taken for all the subjects participating in the study; possible causes and duration of tinnitus were noted for all the participants. The possible causes for the majority of subjects were idiopathic in nature with few reporting noise exposures as possible causes. The duration of tinnitus varied between 1 month to 3 years with a mean duration of 16.5 months. After this, they underwent audiological assessment with Pure Tone Audiometry, Tympanometry, pitch and loudness matching (only for individuals with tinnitus), and Middle Latency Response.

2.2.1. Pure Tone Audiometry

All the subjects were assessed with otoscopic examination with Heine Otoscope 3000 to check the status of external auditory canal and tympanic membrane. Pure tone audiometry was assessed with a GSI Audiostar Pro two-channel diagnostic audiometer (modified Hughson Westlake procedure) to track the thresholds from 250 Hz to 8 KHz frequencies for air conduction and thresholds from 250 Hz to 4 KHz for bone conduction measurements. TDH 50 supra-aural headphones and RadioEar B71 bone vibrator were used to obtain air and bone conduction thresholds, respectively.

2.2.2. Tympanometry

A Tympanometry test was done using a GSI Tympstar ProTM Middle ear analyzer in which 226 Hz was used as a probe tone with a pump rate of 200 dapa/sec to administer the test to find out Middle ear pathologies. Static admittance with 0.3 to 1.5 mL, Ear canal volume of 0.6 to 1.5 cm3 (Roeser, 2000) and tympanometric type of ‘A’ were considered normal and proceeded with the test procedures.

2.2.3. Tinnitus (Pitch and Loudness) Matching Test

For individuals with tinnitus, Pitch and Loudness matching was carried out to understand the nature of tinnitus. In pitch matching, a series of different frequency tones was given to the individuals, and their task was to perfectly match this tone to the pitch of the tinnitus. In loudness matching, the task was the same as the pitch, but here they had to match the loudness to that of their tinnitus (McFadden, 1982).

2.2.4. Tinnitus Handicap Inventory (THI)

The Tinnitus Handicap Inventory (THI) questionnaire, was assessed for all the subjects participating in the study. The Kannada version of THI (Zacharia et al., 2012) was used in the current study to assess tinnitus-related distress in 3 major sub-domains. It consists of 25 questions divided into three subscales: functional, emotional, and catastrophic. The emotional domain reflects the affective responses associated with tinnitus, including anxiety, and depressive symptoms. The functional domain evaluates the influence of tinnitus on routine activities and social or occupational functioning, such as communication, household tasks, and stress handling. The catastrophic domain reflects more severe reactions, encompassing perceptions of overwhelming distress, and loss of control. For Scoring, responses ranging from Yes, Sometimes, and No, and is scored as 4, 2, and 0, respectively, for each response, and the total scores are calculated. Total scores were calculated and graded tinnitus into 5 grades: 0-16 slight or no handicap, 18-36 mild handicap, 38-56 moderate handicap, 58-76 severe handicap, and 78-100 catastrophic handicap.

2.2.5. Auditory Middle Latency Response (AMLR)

Lastly, the Middle Latency Response test was carried out using IHS SmartEP version 5.54.10 developed by (Intelligent Hearing Systems Corp., Miami, FL), by using ER3A inserts and cup electrodes. A two-channel vertical electrode montage was used to record AMLR by placing the positive electrode on the higher forehead, the ground electrode on the lower forehead, and the other two negative electrodes on each mastoid; inter-electrode impedance was maintained to be less than or equal to 1 Kohm. Tone burst stimulus of 500Hz, 1KHz, 2KHz, and 4KHz with duration kept constant at 5ms (2-1-2 rise and fall time), with the rate of 7.1/s, at 50 dB SL level to elicit robust MLR (Table 1). The filter setting was set to 10 Hz for a high pass and 1500 Hz for a low pass with a gain of 50,000.

Table 1. MLR Protocol used for testing.

Stimulus	Toneburst (500 Hz, 1KHz, 2KHz, and 4KHz)
dB SL: decibel sensation level, Hz: Hertz, KHz: kilohertz, ms: milliseconds.
Rate	7.1 stimuli per second
Stimulus Level	50 dB SL
Filter: High Pass Low Pass	10 Hz 1500 Hz
Sweeps	1000
Duration	5ms (2-1-2)
Gain	50,000

Offline analysis procedures like baseline correction and Filtering were applied on each recorded waveform using standard analysis procedures. In the current study, across groups, Na mean amplitude and peak latency were measured between 15 to 25 msec and Pa mean amplitude and peak latency were measured between 25 to 35 msec. The peaks of MLR were marked by two experienced audiologists in the field of electrophysiology who were not part of the current study. The latency and amplitude values for both Na and Pa components in both groups were entered in MS Excel files and exported to SPSS version 22 (SPSS Inc., Chicago) for statistical analysis.

2.3. Statistical analysis

The latency and amplitude for all the MLR components were entered in an Excel file and imported to IBM SPSS version 29 software for Windows (IBM Corporation, Armonk, NY, USA) for statistical estimation. The variables were checked for normality using the Shapiro-Wilk test, and the results indicated that all variables were normally distributed. Hence, Analysis of Covariance (ANCOVA) was performed separately on latency and amplitude of each MLR components with ear (right vs Left) and frequency (500 Hz vs 1 KHz vs 2KHz vs 4 KHz) as with in subject variable and Group (Control vs Tinnitus) as between subject variable and PTA thresholds and Age as covariate. The findings suggest no statistically significant impact of the covariate on latency and amplitude of MLR components. Additionally, to assess the correlation between Pa amplitude and THI scores Karl Pearson’s correlation and scatterplots were used.

3. Results

The study recruited a total of 25 controls and 25 individuals with tinnitus, with their age ranging between 20 to 60 years. The control group consisted of 13 males and 12 females, normal hearing individuals with no tinnitus, with their mean age of 33.26 years. The tinnitus group consisted of 14 males and 11 females with mild hearing loss and tinnitus, with their mean age of 48.42 years. The mean PTA for the control group was 9.83 dB HL and 10.16 dB HL for right and left ears, respectively, and the tinnitus group was 25.19 dB HL for right and 27.97 dB HL for left ears. During the tinnitus matching tests, the individuals matched the pitch within the range of 250 Hz to 6 KHz. With respect to tinnitus pitch, 14 subjects matched the pitch to 4 KHz, 2 subjects to 6 KHz, 2 subjects to 2 KHz, and 1 each to 3 KHz, 1 KHz and 250 Hz pure tones. The majority of individuals had high frequency hearing loss, which is frequently associated with high pitch tinnitus. This relationship is well-documented across multiple studies (Cuesta and Cobo, 2021).

THI scores also varied from mild impact to severe impact on activities of daily living. Normative scores of classifications of THI are 0 to 16 (Slight/No handicap), 18 to 36 (Mild handicap), 38 to 56 (Moderate handicap), 58 to 76 (Severe handicap), and 78 to 100 (Catastrophic handicap) (Newman et al., 1996). Further, the demographic details statistics are provided in (Table 2).

Table 2. Demographic details for both the groups.

Group	Mean age (years)	PTA mean (dB HL)	Tinnitus pitch (Hz) Mean (SD):	THI scores	THI Mean	THI SD
PTA: Pure Tone Average, THI: Tinnitus Handicap Inventory, dB HL: Decibel Hearing Level, Hz: Hertz, SD: Standard Deviation.
Control	33.26 years	Right: 9.83 dB HL Left: 10.16 dB HL	NA	NA
Tinnitus	48.42 years	Right: 25.19 dB HL Left: 27.97 dB HL	3630 Hz (1992) Hz	Slight/No - 0 Mild -6 Moderate- 11 Severe – 4 Catastrophic- 0	NA 29.1 47.09 65.5 NA	NA 3.3 3.75 5.72 NA

Analysis of Covariance (ANCOVA) was performed separately on latency and amplitude of each MLR components with ear (right vs Left) and frequency (500 Hz vs 1 KHz vs 2KHz vs 4 KHz) as with in subject variable and Group (Control vs Tinnitus) as between subject variable and PTA thresholds and Age as covariate. The findings suggest no statistically significant impact of the covariate on latency (PTA – [F(1,42)= 0.643, p=0.12, η= 0.015], Age – [PTA – [F(1,42)= 0.452, p=0.09, η= 0.015]) and amplitude (PTA – [F(1,42)= 0.113, p=0.15, η= 0.017], Age – [PTA – [F(1,42)= 0.542, p=0.08, η= 0.032]) of MLR components. The results are discussed separately for each component. Descriptive statistics are provided in (Table 3).

Table 3. Latency and Amplitude values of all the MLR components, along with the mean and SD.

Component	Ear	Frequency	Mean		SD
			CG	TG	CG	TG
CG: Control Group, TG: Tinnitus Group, SD: Standard Deviation, ms: milliseconds, µV: microvolt, Hz: Hertz, Rt: Right ear, Lt: Left ear, Lat: Latency, Amp: Amplitude
Na Amp	Rt	500 Hz	-0.40 µV	-0.42 µV	0.18 µV	0.19 µV
		1 KHz	-0.47 µV	-0.34 µV	0.16 µV	0.24 µV
		2 KHz	-0.40 µV	-0.30 µV	0.18 µV	0.24 µV
		4 KHz	-0.42 µV	-0.32 µV	0.17 µV	0.17 µV
	Lt	500 Hz	-0.51 µV	-0.33 µV	0.18 µV	0.10 µV
		1 KHz	-0.48 µV	-0.38 µV	0.21 µV	0.14 µV
		2 KHz	-0.45 µV	-0.31µV	0.20 µV	0.15 µV
		4 KHz	-0.41 µV	-0.36 µV	0.19 µV	0.18 µV
Na Lat	Rt	500 Hz	20.07 ms	20.61 ms	1.63 ms	2.0 ms
		1 KHz	20.33 ms	20.24 ms	1.27 ms	2.24 ms
		2 KHz	18.95 ms	19.86 ms	0.94 ms	1.88 ms
		4 KHz	18.64 ms	20.20 ms	1.21 ms	1.87 ms
	Lt	500 Hz	19.83 ms	19.91 ms	1.46 ms	2.13 ms
		1 KHz	20.01 ms	19.32 ms	1.43 ms	1.59 ms
		2 KHz	19.34 ms	19.53 ms	1.57 ms	1.63 ms
		4 KHz	19.95 ms	10.51 ms	2.03 ms	1.59 ms
Pa Amp	Rt	500 Hz	0.58 µV	1.33 µV	0.23 µV	0.39 µV
		1 KHz	0.51 µV	1.25 µV	0.22 µV	0.41 µV
		2 KHz	0.54 µV	1.29 µV	0.22 µV	0.49 µV
		4 KHz	0.57 µV	1.19 µV	0.24 µV	0.52 µV
	Lt	500 Hz	0.51 µV	1.08 µV	0.14 µV	0.58 µV
		1 KHz	0.52 µV	1.19 µV	0.18 µV	0.47 µV
		2 KHz	0.49 µV	1.21 µV	0.16 µV	0.53 µV
		4 KHz	0.49 µV	1.24 µV	0.24 µV	0.48 µV
Pa Lat	Rt	500 Hz	30.80 ms	31.45 ms	1.98 ms	2.60 ms
		1 KHz	30.83 ms	31.56 ms	2.55 ms	3.34 ms
		2 KHz	28.96 ms	29.73 ms	2.71 ms	3.22 ms
		4 KHz	29.89 ms	30.62 ms	2.63 ms	3.78 ms
	Lt	500 Hz	31.06 ms	31.73 ms	2.81 ms	2.48 ms
		1 KHz	30.51 ms	30.87 ms	2.25 ms	2.20 ms
		2 KHz	29.53 ms	30.28 ms	2.90 ms	2.13 ms
		4 KHz	30.10 ms	30.53 ms	2.43 ms	1.38 ms
Nb Amp	Rt	500 Hz	-0.40 µV	-0.42 µV	0.19 µV	0.22 µV
		1 KHz	-0.50 µV	-0.39 µV	0.28 µV	0.19 µV
		2 KHz	-0.45 µV	-0.45 µV	0.24 µV	0.25 µV
		4 KHz	-0.39 µV	-0.41 µV	0.21 µV	0.21 µV
	Lt	500 Hz	-0.37 µV	-0.40 µV	0.26 µV	0.13 µV
		1 KHz	-0.41 µV	-0.49 µV	0.25 µV	0.23 µV
		2 KHz	-0.35 µV	-0.52 µV	0.25 µV	0.15 µV
		4 KHz	-0.39 µV	-0.30 µV	0.22 µV	0.21 µV
Nb Lat	Rt	500 Hz	45.95 ms	47.03 ms	2.33 ms	2.52 ms
		1 KHz	46.13 ms	46.04 ms	2.35 ms	2.17 ms
		2 KHz	44.85 ms	45.41 ms	2.46 ms	2.53 ms
		4 KHz	45.45 ms	46.33 ms	2.25 ms	2.35 ms
	Lt	500 Hz	47.31 ms	45.32 ms	2.20 ms	1.72 ms
		1 KHz	47.92 ms	45.31 ms	2.80 ms	1.32 ms
		2 KHz	46.43 ms	44.73 ms	1.77 ms	1.95 ms
		4 KHz	46.34 ms	45.70 ms	2.54 ms	2.02 ms
Pb Amp	Rt	500 Hz	0.49 µV	0.28 µV	0.29 µV	0.20 µV
		1 KHz	0.39 µV	0.29 µV	0.23 µV	0.18 µV
		2 KHz	0.37 µV	0.35 µV	0.18 µV	0.21 µV
		4 KHz	0.36 µV	0.38 µV	0.23 µV	0.21 µV
	Lt	500 Hz	0.43 µV	0.26 µV	0.27 µV	0.17 µV
		1 KHz	0.38 µV	0.31 µV	0.21 µV	0.20 µV
		2 KHz	0.36 µV	0.32 µV	0.19 µV	0.18 µV
		4 KHz	0.40 µV	0.41 µV	0.19 µV	0.12 µV
Pb Lat	Rt	500 Hz	58.48 ms	57.74 ms	2.28 ms	2.83 ms
		1 KHz	58.06 ms	56.64 ms	2.53 ms	4.00 ms
		2 KHz	57.64 ms	55.92 ms	2.72 ms	3.95 ms
		4 KHz	56.77 ms	56.70 ms	3.53 ms	3.56 ms
	Lt	500 Hz	57.96 ms	57.07 ms	3.15 ms	1.34 ms
		1 KHz	57.73 ms	57.32 ms	2.26 ms	2.26 ms
		2 KHz	56.73 ms	58.14 ms	2.45 ms	2.41 ms
		4 KHz	56.55 ms	56.13 ms	3.27 ms	1.58 ms

3.1. Na Amplitude

Results revealed there was no significant difference between the two groups on Na amplitude (F (1, 42) = 1.315, p = 0.410, η = 0.182). Though not statistically significant, controls showed slightly larger Na amplitude when compared to that of the tinnitus individual (Fig 1). However, neither the main effect of frequency (F (2.615, 109.832) = 2.451, p = 0.10, η = 0.055) and ear (F (1, 42) = 0.708, p = 0.12, η = 0.017) nor the interaction effect between any of the variables reached significant findings (F (3, 126) = 0.136, p = 0.172, η = 0.003).

Figure 1.

Box plot of Na amplitude (µV) at different frequencies between controls and tinnitus group.

3.2. Pa Amplitude

Results revealed a significant main effect of group (F (1, 42) = 6.118, p = 0.046, η = 0.184) on Pa amplitude, where Pa amplitude was larger in tinnitus individuals when compared to controls (Fig 2 and 3). However, neither the main effect of frequency (F (3, 126) = 1.249, p = 0.579, η = 0.029) and ear (F (1, 42) = 0.738, p = 0.579, η = 0.017), nor the interaction effect (F (3, 126) = 0.487, p = 0.545, η = 0.011) between any of the variables reached significant findings.

Figure 2.

Bar graph depicting Mean, SD, and Individual points of subjects in tinnitus and control groups at different frequencies.

Figure 3.

Box plot of Pa amplitude (µV) at different frequencies between controls and tinnitus group showing significant values.

3.3. Nb Amplitude

Results revealed there was no statistically significant differences between the two groups (F (1, 42) = 0.871, p = 0.744, η = 0.020), group (F (1, 42) = 0.90, p = 0.766, η = 0.002) and frequency (F (3, 126) = 4.141, p = 0.744, η = 0.090) on Nb amplitude. Further the interaction effect between any variables was not significant (F (3, 126) = 0.480, p = 0.119, η = 0.011). Though not significant, but amplitude was larger in the tinnitus group than the control group.

3.4. Pb Amplitude

Results revealed there was no statistically significant differences between the two groups (F (1, 42) = 3.009, p = 0.090, η = 0.067). There was also no significant main effect of ear and the frequency (F (2.533, 106.381) = 0.775, p = 0.37, η = 0.018) and (F (2.477, 104.026) = 1.493, p = 0.09, η = 0.034) on Pb amplitude. Main effect nor interaction effect showed no significant impact.

3.5. Latency effects on MLR components (Na, Pa, Nb, Pb)

Results showed no significant differences in the ear, group and interaction effect on the latencies for all the components of the MLR. However all the latency component of MLR showed a main effect on frequency (F (3, 126) = 4.127, p = 0.090, η = 0.089) and other three components showed no significant findings. Post hoc analysis using Bonferroni correction revealed a significant difference between 500 Hz and 4KHz (p=0.03) and found no significant difference between 500 Hz and 1 KHz (p=0.10), 500 Hz and 2 KHz (p=0.21). High frequencies showed shorter latencies and low frequencies had prolonged latencies for all the components. Further the interaction effect between any variables was not significant (F (3, 126) = 2.232, p = 0.212, η = 0.050).

3.6. THI scores and MLR

To achieve this, Karl Pearson correlation coefficient and scatter plots were used to assess the magnitude and direction of correlation. Results showed no significant correlation between THI scores and any of the outcome measures except for Pa amplitude (Table 4). There was a weak negative but non-significant correlation between Pa amplitude and THI scores, where greater THI scores lead to a decrease in Pa amplitude (Fig. 4) (r = - 0.377, p = 0.092). Additionally, correlation analysis was also carried out to explore the association between duration of tinnitus and MLR amplitude and latency. There was no significant correlation between duration of tinnitus and MLR amplitude and latency (r= 0.112, p= 0.214).

Table 4. Correlation between MLR components v/s THI scores.

THI scores v/s MLR components amplitude	r value	P-values
THI: Tinnitus Handicap Inventory, MLR: Middle Latency Response
THI v/s Na amplitude	0.11	0.12
THI v/s Pa amplitude	- 0.377	0.092
THI v/s Nb amplitude	0.19	0.15
THI v/s Pb amplitude	0.21	0.87

Figure 4.

Scatterplot comparing between total THI scores and amplitude of Pa component (µV) of Middle Latency Response.

4. Discussion

As tinnitus is multifaceted in nature and will be associated with many other conditions, assessment of tinnitus poses a challenge for clinicians to deal with tinnitus. Tinnitus can stem from various causes and affect brain activities differently at different stages(Moller, 2011). Few other studies also highlight on systemic disease like hypertension, cardiovascular disease etc., where they observed the spike in the glucose and LDL levels (Low-Density Lipoprotein) were co-related with the severity of tinnitus (Molnár et al., 2025). And it may interfere with various aspects of daily activities and social well-being leading to anxiety, stress, depression, and frustration (Kalsotra et al., 2022; Marín and Soto, 2022). From the Jastreboff’s neurophysiological theory of tinnitus it is noted that the perception of tinnitus activates the regions in and around the structures of thalamus and other non-auditory areas of the brain such as limbic, and autonomic nervous system.

Several neuroimaging tests like CT, MRI, and fMRI have indicated structural changes in the subcortical areas like the thalamus and caudate nucleus. fMRI studies have shown a reduction in neural inhibition in the areas of thalamocortical pathways hence creating more neural noise. MLR which is an electrophysiological test and is very sensitive in finding out minute changes of the neural configurations at the level of thalamus. MLR is effective in evaluating lesions or dysfunctions in the central auditory nervous system. It is particularly useful for detecting auditory processing disorders and lesions, and it can provide insights into the integrity of the auditory thalamocortical pathway (Musiek and Nagle, 2018), and hence the current study aimed to explore the effect of tinnitus on latency and amplitude of MLR.

The study findings showed noticeable changes in amplitude of all the MLR components, but the amplitude differences seen in the Pa component reached statistical significance and are worth exploring. Pa amplitude showed a significant difference; amplitude was larger for tinnitus individuals than that of controls (Fig. 5 & 6).

Figure 5.

MLR waveforms of normal individual with top wave representing 500 Hz followed by 1000 Hz, 2000 Hz, and 4000 Hz (bottom), (x-axis shows latency in ms and y-axis shows amplitude in µV)

Figure 6.

MLR waveforms of tinnitus subjects with top wave representing 500 Hz followed by 1000 Hz, 2000 Hz, and 4000 Hz (bottom), (x-axis shows latency in ms and y-axis shows amplitude in µV)

Pa has multiple neural generators including Heschl gyrus and sulcus, the planum temporale, and the superior temporal gyrus are simultaneously activated to generate the Pa component. Enhancement in Pa amplitude is atypical and could be associated with increased central gain as compensation for peripheral pathologies. According to central gain theory, tinnitus and hyperacusis result from a compensatory increase in gain or neural amplification in the central auditory system to compensate for a loss of sensory input from the cochlea (Auerbach et al., 2019). The findings of the current study are in line with a few other studies in the literature that would throw some light on this atypical finding. Study found larger Auditory Steady State Response (ASSR) amplitudes in tinnitus subjects and stated that the reason for the high ASSR amplitudes in the auditory area is cortical hyperexcitability in the tinnitus participants relative to the normal controls (Diesch et al., 2012). Enhanced amplitude for Na and Pa component was also reported by Singh et al. (2011), who speculated the findings could be because of the loss of surrounding inhibition seen in the auditory cortex (Singh et al., 2011). Tinnitus and hearing loss can be considered as two sides of a coin and the association between each other is very well established. Tinnitus is considered as a symptom rather than a disease or disorder, and it is associated with alterations in the pathophysiology of the cochlea and auditory pathway, which may be associated with hearing loss. The authors have chosen Analysis of Covariance (ANCOVA) to establish statistical significance with hearing loss as covariate and the findings revealed no significant impact of the covariate on latency and amplitude of MLR components. However we cannot fully rule out the contribution of hearing loss in the established finding and the enhanced MLR amplitude could be attributed to hearing loss, tinnitus, or an interaction between the two.

The correlation analysis revealed a week negative correlation between THI scores which suggested that as THI scores increased Pa amplitude reduced. These findings suggest that Pa amplitude is larger in individuals with less severe tinnitus and vice versa. This is a novel finding, and more research is needed to arrive at a definite conclusion. Sadeghijam et al. (2022) recorded ASSR in groups with higher and lower THI scores and reported similar findings where the ASSR amplitude was larger in individuals with lower THI scores. The region of interests analysis revealed pronounced differences in anterior frontal regions right hemispheres which are linked with attention and cognitive networks. They speculated that lesser involvement of prefrontal and attention network in individuals with lower THI scores may lead to higher amplitude because of decreased inhibition (Sadeghijam et al., 2022). Neuroimaging techniques have demonstrated higher frontal brain activation in more severe tinnitus. Hence, persistent chronic tinnitus could lead to increased activation in the prefrontal cortex, leading to more inhibition and a reduction in amplitude. However, more systematic multichannel studies with source analysis data may be needed to study the role of the prefrontal cortex in tinnitus pathophysiology.

Though the study tried to address the majority of methodological limitations in the literature, there are certain limitations which has to be addressed in future research. The study recorded MLR in small group of tinnitus and hence small sample size is a limitation of the study. Individuals with tinnitus experience tinnitus in the right, left or both ears making it highly variable between the subjects. The severity of the tinnitus also influences the subjects, and they will have varying degrees of severity for all the subjects. All these factors will limit the outcomes of the study, and hence making it difficult to generalize the study findings to a clinical setup. Future studies should focus on developing more controlled experiments to study the effectiveness of objective tools in the assessment of tinnitus.

5. Summary and conclusion

The study aimed to explore the clinical utility of MLR as an objective tool in tinnitus assessment. The findings revealed an increased amplitude in Pa components in tinnitus individuals, which may be due to the increased spontaneous activity resulting from reduced inhibition, contributing to such changes. Pa amplitude also showed a correlation with THI scores where greater THI scores result in reduced Pa amplitudes. Overall, the study findings highlight certain neurophysiological differences between controls and tinnitus subjects, indicating the effectiveness of objective tools in assessing tinnitus. Hence, MLR could be served as objective evidence to study the neurophysiological changes associated with tinnitus at the level of subcortex. However, the findings have to be replicated in a larger population with more stringent methodology to establish reliability and diagnostic accuracy.

Funding Statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.