Factors That Impact the Long-Term Outcome of Postconcussive Dizziness Among Post-9/11 Veterans.

PURPOSE: The primary aim of this study was to examine the factors associated with long-term outcomes of postconcussive disruptive dizziness in Veterans of the post-9/11 wars. METHOD: For this observational cohort study, the Neurobehavioral Symptom Inventory-Vestibular subscale (NSI-V) score was used as an outcome measure for dizziness in 987 post-9/11 Veterans who indicated disruptive dizziness at an initial Veterans Health Administration Comprehensive Traumatic Brain Injury Evaluation (CTBIE). An NSI-V change score was calculated as the difference in the scores obtained at the initial CTBIE and on a subsequent survey. Differences in the NSI-V change scores were examined for demographics, injury characteristics, comorbidities, and vestibular and balance function variables, and multiple linear regression analyses were used to explore associations among the variables and the NSI-V change score. RESULTS: The majority of Veterans (61%) demonstrated a decrease in the NSI-V score, suggesting less dizziness on the survey compared with the CTBIE; 16% showed no change; and 22% had a higher score. Significant differences in the NSI-V change score were observed for traumatic brain injury (TBI) status, diagnoses of post-traumatic stress disorder (PTSD), headache and insomnia, and vestibular function. Multivariate regressions revealed significant associations between the NSI-V change score and the initial CTBIE NSI-V score, education level, race/ethnicity, TBI status, diagnoses of PTSD or hearing loss, and vestibular function. CONCLUSIONS: Postconcussive dizziness can continue for years following an injury. Factors associated with poor prognosis include TBI, diagnoses of PTSD or hearing loss, abnormal vestibular function, increased age, identification as a Black Veteran, and high school education level.

Vestibular and balance function in veterans with chronic dizziness associated with mild traumatic brain injury and blast exposure.

The purpose of this study was to examine vestibular and balance function in individuals with chronic dizziness associated with mTBI/blast. A prospective case-control study design was used to examine ocular motor, vestibular function, and postural stability in veterans with symptoms of dizziness and/or imbalance following an mTBI or blast exposure (n = 77) and a healthy control group (n = 32). Significant group differences were observed for saccadic accuracy, VOR gain during slow harmonic acceleration at 0.01 Hz, cervical vestibular evoked myogenic potentials asymmetry ratio, composite equilibrium score on the sensory organization test, total Dynamic Gait Index score, and gait. The frequency of test abnormalities in participants with mTBI/blast ranged from 0 to 70% across vestibular, ocular motor, and balance/gait testing, with the most frequent abnormalities occurring on tests of balance and gait function. Seventy-two percent of the mTBI/blast participants had abnormal findings on one or more of the balance and gait tests. Vestibular test abnormalities occurred in ~34% of the individuals with chronic dizziness and mTBI/blast, and abnormalities occurred more frequently for measures of otolith organ function (25% for cVEMP and 18% for oVEMP) than for measures of hSCC function (8% for SHA and 6% for caloric test). Abnormal ocular motor function occurred in 18% of the mTBI/blast group. These findings support the need for comprehensive vestibular and balance assessment in individuals with dizziness following mTBI/blast-related injury.

Disruptive Dizziness Among Post-9/11 Veterans With Deployment-Related Traumatic Brain Injury.

OBJECTIVE: To identify disruption due to dizziness symptoms following deployment-related traumatic brain injury (TBI) and factors associated with receiving diagnoses for these symptoms. SETTING: Administrative medical record data from the Department of Veterans Affairs (VA). PARTICIPANTS: Post-9/11 veterans with at least 3 years of VA care who reported at least occasional disruption due to dizziness symptoms on the comprehensive TBI evaluation. DESIGN: A cross-sectional, retrospective, observational study. MAIN MEASURES: International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes of dizziness, vestibular dysfunction, and other postconcussive conditions; neurobehavioral Symptom Inventory. RESULTS: Increased access to or utilization of specialty care at the VA was significant predictors of dizziness and/or vestibular dysfunction diagnoses in the fully adjusted model. Veterans who identified as Black non-Hispanic and those with substance use disorder diagnoses or care were substantially less likely to receive dizziness and vestibular dysfunction diagnoses. CONCLUSIONS: Access to specialty care was the single best predictor of dizziness and vestibular dysfunction diagnoses, underscoring the importance of facilitating referrals to and utilization of specialized, comprehensive clinical facilities or experts for veterans who report disruptive dizziness following deployment-related TBI. There is a clear need for an evidence-based pathway to address disruptive symptoms of dizziness, given the substantial variation in audiovestibular tests utilized by US providers by region and clinical specialty. Further, the dearth of diagnoses among Black veterans and those in more rural areas underscores the potential for enhanced cultural competency among providers, telemedicine, and patient education to bridge existing gaps in the care of dizziness.

Effects of Noise Exposure on the Vestibular System: A Systematic Review.

Despite our understanding of the impact of noise-induced damage to the auditory system, much less is known about the impact of noise exposure on the vestibular system. In this article, we review the anatomical, physiological, and functional evidence for noise-induced damage to peripheral and central vestibular structures. Morphological studies in several animal models have demonstrated cellular damage throughout the peripheral vestibular system and particularly in the otolith organs; however, there is a paucity of data on the effect of noise exposure on human vestibular end organs. Physiological studies have corroborated morphological studies by demonstrating disruption across vestibular pathways with otolith-mediated pathways impacted more than semicircular canal-mediated pathways. Similar to the temporary threshold shifts observed in the auditory system, physiological studies in animals have suggested a capacity for recovery following noise-induced vestibular damage. Human studies have demonstrated that diminished sacculo-collic responses are related to the severity of noise-induced hearing loss, and dose-dependent vestibular deficits following noise exposure have been corroborated in animal models. Further work is needed to better understand the physiological and functional consequences of noise-induced vestibular impairment in animals and humans.

Association of Traumatic Brain Injury With Vestibular Dysfunction and Dizziness in Post-9/11 Veterans.

OBJECTIVE: To describe the prevalence and impact of vestibular dysfunction and nonspecific dizziness diagnoses and explore their associations with traumatic brain injury (TBI) severity, mechanism, and postconcussive comorbidities among post-9/11 veterans. SETTING: Administrative medical record data from the US Departments of Defense and Veterans Affairs (VA). PARTICIPANTS: Post-9/11 veterans with at least 3 years of VA care. DESIGN: Cross-sectional, retrospective, observational study. MAIN MEASURES: International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes for TBI, vestibular dysfunction, dizziness, and other commonly associated postconcussive conditions; Neurobehavioral Symptom Inventory. RESULTS: Of the 570 248 post-9/11 veterans in this sample, 0.45% had a diagnosis of vestibular dysfunction and 2.57% had nonspecific dizziness. Those with either condition were more likely to have evidence of TBI (57.11% vs 28.51%) and reported more disruption from neurobehavioral symptoms. Blast and nonblast injuries were associated with greater symptom disruption, particularly in combination. CONCLUSIONS: There was a consistent, significant association between TBI and vestibular dysfunction or nonspecific dizziness, after controlling for sociodemographic factors, injury mechanism, and comorbid conditions. Given that most deployed post-9/11 veterans report blast and/or nonblast injuries, the need for prompt identification and management of these conditions and symptoms is clear.

Sensory dysfunction and traumatic brain injury severity among deployed post-9/11 veterans: a chronic effects of neurotrauma consortium study.

OBJECTIVES: To describe the prevalence of sensory dysfunction (i.e. auditory, visual, vestibular, chemosensory and multiple sensory problems) and explore associations with traumatic brain injury (TBI) severity and injury mechanism among deployed Post-9/11 Veterans. METHODS: This retrospective cohort analysis used Departments of Defense and Veterans Affairs diagnostic codes and administrative data. RESULTS: Among the 570,248 Veterans in this cohort, almost 23% had at least one diagnosis of sensory dysfunction. In the multinomial regression analysis, the odds of all types of sensory dysfunction were greater among those with any TBI relative to those with no TBI. The odds for auditory or multisensory problems were higher among those that indicated exposure to blast. In particular, exposure to quaternary blast injury (e.g. crush, respiratory and burn injuries) was associated with increased odds for auditory, visual, vestibular and multisensory problems. CONCLUSIONS: Sensory problems affect a substantial number of deployed Post-9/11 Veterans and are more common among those with TBI or with exposure to deployment-related blast exposure. Because sensory problems profoundly impact quality of life, their identification and enhanced education and therapy are vital tools to improve prognosis for these relatively young Veterans.

A Benign Paroxysmal Positional Vertigo Triage Clinic.

PURPOSE: The purpose of this study was to evaluate the effectiveness of triaging patients with motion-provoked dizziness into a benign paroxysmal positional vertigo (BPPV) clinic. METHOD: A retrospective chart review was performed of veterans who were tested and treated for BPPV in a triaged BPPV clinic and veterans who were tested and treated for BPPV in a traditional vestibular clinic. RESULTS: The BPPV triage clinic had a hit rate of 39%. On average, the triaged BPPV clinic reduced patient wait times by 23 days relative to the wait times for the traditional vestibular clinic while also reducing patient costs. CONCLUSION: Triaging patients with BPPV is one method to improve access to evaluation and treatment and a mechanism for the effective use of clinic time and resources.

Characteristics and Treatment Outcomes of Benign Paroxysmal Positional Vertigo in a Cohort of Veterans.

BACKGROUND: The Mountain Home Veterans Affairs (VA) Medical Center has been diagnosing and treating veterans with benign paroxysmal positional vertigo (BPPV) for almost 2 decades. The clinic protocol includes a 2-week follow-up visit to determine the treatment outcome of the canalith repositioning treatment (CRT). To date, the characteristics of BPPV and treatment efficacy have not been reported in a cohort of veterans with BPPV. PURPOSE: To determine the prevalence and characteristics of veterans diagnosed with BPPV in a Veterans Affairs Medical Center Audiology Clinic and to examine treatment outcomes. RESEARCH DESIGN: Retrospective chart review. STUDY SAMPLE: A total of 102 veterans who tested positive for BPPV in the Vestibular Clinic at the Mountain Home VA Medical Center from March 2010 to August 2011. RESULTS: In 102 veterans who were diagnosed with BPPV, the posterior semicircular canal was most often involved (75%), motion-provoked vertigo was the most common symptom (84%), and the majority (43%) were diagnosed with BPPV in their sixth decade. The prevalence of BPPV in the Audiology Vestibular Clinic was 15.6%. Forty-one percent of veterans reported a symptom onset within 12 months of treatment for BPPV; however, 36% reported their symptoms began > 36 months prior to treatment. CRT was effective (negative Dix-Hallpike/roll test) in most veterans (86%) following 1 treatment appointment (M = 1.6), but more than half reported incomplete symptom resolution (residual dizziness) at the follow-up appointment. Eighteen percent of veterans experienced a recurrence (M = 1.8 years; SD = 1.7 years). CONCLUSIONS: The characteristics and treatment outcomes of BPPV in our veteran cohort was similar to what has been reported in the general population. Future work should focus on improving the timeliness of evaluation and treatment of BPPV and examining the time course and management of residual dizziness.

Vestibular consequences of mild traumatic brain injury and blast exposure: a review.

The purpose of this article is to review relevant literature on the effect of mild traumatic brain injury (mTBI) and blast injury on the vestibular system. Dizziness and imbalance are common sequelae associated with mTBI, and in some individuals, these symptoms may last for six months or longer. In war-related injuries, mTBI is often associated with blast exposure. The causes of dizziness or imbalance following mTBI and blast injuries have been linked to white matter abnormalities, diffuse axonal injury in the brain, and central and peripheral vestibular system damage. There is some evidence that the otolith organs may be more vulnerable to damage from blast exposure or mTBI than the horizontal semicircular canals. In addition, benign paroxysmal positional vertigo (BPPV) is a common vestibular disorder following head injury that is treated effectively with canalith repositioning therapy. Treatment for (non-BPPV) mTBI-related vestibular dysfunction has focused on the use of vestibular rehabilitation (VR) augmented with additional rehabilitation methods and medication. New treatment approaches may be necessary for effective otolith organ pathway recovery in addition to traditional VR for horizontal semicircular canal (vestibulo-ocular reflex) recovery.

Vestibular, balance, microvascular and white matter neuroimaging characteristics of blast injuries and mild traumatic brain injury: Four case reports.

BACKGROUND: Case reports are presented on four Veterans, aged 29-46 years, who complained of chronic dizziness and/or postural instability following blast exposures. Two of the four individuals were diagnosed with mild traumatic brain injury and three of the four were exposed to multiple blasts. Comprehensive vestibular, balance, gait, audiometry and neuroimaging procedures were used to characterize their injuries. CASE REPORT: Vestibular assessment included videonystagmography, rotary chair and cervical and ocular vestibular evoked myogenic potentials. Balance and gait testing included the sensory organization test, preferred gait speed and the dynamic gait index. Audiometric studies included pure tone audiometry and middle-ear measurements. Neuroimaging procedures included high resolution structural magnetic resonance imaging, susceptibility-weighted imaging and diffusion-tensor imaging. FINDINGS: Based on the neuroimaging and vestibular and balance test results, it was found that all individuals had diffuse axonal injuries and all had one or more micro-hemorrhages or vascular anomalies. Three of the four individuals had abnormal vestibular function, all had abnormally slow walking speeds and two had abnormal gait and balance dysfunction. CONCLUSION: The use of contemporary neuroimaging studies in conjunction with comprehensive vestibular and balance assessment provided a better understanding of the pathophysiology and pathoanatomy of dizziness following blast exposures than standard vestibular and balance testing alone.

Vestibular Assessment and Rehabilitation: Ten-Year Survey Trends of Audiologists' Opinions and Practice.

BACKGROUND: The past decade has yielded changes in the education and training of audiologists and technological advancements that have become widely available for clinical balance function testing. It is unclear if recent advancements in vestibular instrumentation or the transition to an AuD degree have affected audiologists' vestibular clinical practice or opinions. PURPOSE: The purpose of this study was to examine predominant opinions and practices for vestibular assessment (VA) and vestibular rehabilitation (VR) over the past decade and between master's- and AuD-level audiologists. METHOD: A 31-question survey was administered to audiologists via U.S. mail in 2003 (N = 7,500) and electronically in 2014 (N = 9,984) with a response rate of 12% and 10%, respectively. RESULTS: There was an increase in the number of audiologists providing vestibular services in the past decade. Most respondents agreed that audiologists were the most qualified professionals to conduct VA. Less than half of the surveyed audiologists felt that graduate training was adequate for VA. AuD-level audiologists were more satisfied with graduate training and felt more comfortable performing VA compared to master's-level audiologists. Few respondents agreed that audiologists were the most qualified professionals to conduct VR or that graduate training prepared them to conduct VR. The basic vestibular test battery was unchanged across surveys and included: calorics, smooth pursuit, saccades, search for spontaneous, positional, gaze and optokinetic nystagmus, Dix-Hallpike, case history, and hearing evaluation. There was a trend toward greater use of air (versus water) calorics, videonystagmography (versus electronystagmography), and additional tests of vestibular and balance function. CONCLUSIONS: VA is a growing specialty area in the field of audiology. Better training opportunities are needed to increase audiologists' knowledge and skills for providing vestibular services. The basic tests performed during VA have remained relatively unchanged over the past 10 yr.

Video Head Impulse Testing (vHIT) and the Assessment of Horizontal Semicircular Canal Function.

BACKGROUND: Vestibular function (specifically, horizontal semicircular canal function) can be assessed across a broad frequency range using several different techniques. The head impulse test is a qualitative test of horizontal semicircular canal function that can be completed at bedside. Recently, a new instrument (video head impulse test [vHIT]) has been developed to provide an objective assessment to the clinical test. Questions persist regarding how this test may be used in the overall vestibular test battery. PURPOSE: The purpose of this case report is to describe vestibular test results (vHIT, rotational testing, vestibular evoked myogenic potentials, and balance and gait performance) in an individual with a 100% unilateral caloric weakness who was asymptomatic for dizziness, vertigo or imbalance. DATA COLLECTION AND/OR ANALYSIS: Comprehensive assessment was completed to evaluate vestibular function. Caloric irrigations, rotary chair testing, vHIT, and vestibular evoked myogenic potentials were completed. RESULTS: A 100% left-sided unilateral caloric weakness was observed in an asymptomatic individual. vHIT produced normal gain with covert saccades. CONCLUSIONS: This case demonstrates the clinical usefulness of vHIT as a diagnostic tool and indicator of vestibular compensation and functional status.

International guidelines for the clinical application of cervical vestibular evoked myogenic potentials: an expert consensus report.

BACKGROUND: Cervical vestibular evoked myogenic potentials (cVEMPs) are electromyogram responses evoked by high-level acoustic stimuli recorded from the tonically contracting sternocleidomastoid (SCM) muscle, and have been accepted as a measure of saccular and inferior vestibular nerve function. As more laboratories are publishing cVEMP data, there is a wider range of recording methods and interpretation, which may be confusing and limit comparisons across laboratories. OBJECTIVE: To recommend minimum requirements and guidelines for the recording and interpretation of cVEMPs in the clinic and for diagnostic purposes. MATERIAL AND METHODS: We have avoided proposing a single methodology, as clinical use of cVEMPs is evolving and questions still exist about its underlying physiology and its measurement. The development of guidelines by a panel of international experts may provide direction for accurate recording and interpretation. RESULTS: cVEMPs can be evoked using air-conducted (AC) sound or bone conducted (BC) vibration. The technical demands of galvanic stimulation have limited its application. For AC stimulation, the most effective frequencies are between 400 and 800 Hz below safe peak intensity levels (e.g. 140 dB peak SPL). The highpass filter should be between 5 and 30 Hz, the lowpass filter between 1000 and 3000 Hz, and the amplifier gain between 2500 and 5000. The number of sweeps averaged should be between 100 and 250 per run. Raw amplitude correction by the level of background SCM activity narrows the range of normal values. There are few publications in children with consistent results. CONCLUSION: The present recommendations outline basic terminology and standard methods. Because research is ongoing, new methodologies may be included in future guidelines.

The effect of noise exposure on the cervical vestibular evoked myogenic potential.

OBJECTIVE: The purpose of this study was to investigate the effects of noise exposure on the cervical vestibular evoked myogenic potential (cVEMP) in individuals with asymmetric noise-induced sensorineural hearing loss (NIHL). DESIGN: A cross-sectional observational study was used to compare cVEMP characteristics in 43 individuals with a history of noise exposure greater in one ear (e.g., the left ear of a right-handed rifle shooter) and asymmetric sensorineural hearing loss consistent with the history of noise exposure and in 14 age-matched controls. The characteristics of hearing loss were examined further for the noise-exposed participants with abnormal cVEMPs and the noise-exposed participants with normal cVEMPs. RESULTS: Thirty-three percent of the noise-exposed participants had abnormal cVEMPs, whereas cVEMPs were present and symmetrical in 100% of the age-matched controls, and cVEMP threshold was greater in the noise-exposed group than in the control group. Abnormal cVEMPs occurred most often in the ears with poorer hearing (or greater NIHL), and the noise-exposed participants who had abnormal cVEMPs had poorer high-frequency pure-tone thresholds (greater NIHL) and greater interaural high-frequency pure-tone threshold differences than the noise-exposed participants with normal cVEMPs. CONCLUSIONS: These findings are consistent with previous studies that suggest that the sacculocollic pathway may be susceptible to noise-related damage. There is emerging evidence that the severity of NIHL is associated with the presence or absence of cVEMPs.

Effects of stimulus and recording parameters on the air conduction ocular vestibular evoked myogenic potential.

BACKGROUND: Vestibular evoked myogenic potentials (VEMPs) have been recorded from the sternocleidomastoid muscle (cervical VEMP or cVEMP) and more recently from the eye muscles (ocular VEMP or oVEMP) in response to air conduction and bone conduction stimuli. Both cVEMPs and oVEMPs are mediated by the otoliths and thereby provide diagnostic information that is complementary to videonystagmography and rotational chair tests. In contrast to the air conduction cVEMP, which originates from the saccule/inferior vestibular nerve, recent evidence suggests the possibility that the air conduction oVEMP may be mediated by the utricle/superior vestibular nerve. The oVEMP, therefore, may provide complementary diagnostic information relative to the cVEMP. There are relatively few studies, however, that have quantified the effects of stimulus and recording parameters on the air conduction oVEMP, and there is a paucity of normative data. PURPOSE: To evaluate the effects of several stimulus and recording parameters on the air conduction oVEMP and to establish normative data for clinical use. RESEARCH DESIGN: A prospective repeated measures design was utilized. STUDY SAMPLE: Forty-seven young adults with no history of neurologic disease, hearing loss, middle ear pathology, open or closed head injury, cervical injury, or audiovestibular disorder participated in the study. DATA COLLECTION AND ANALYSIS: The effects of stimulus frequency, stimulus level, gaze elevation, and recording electrode location on the amplitude and latency of the oVEMP for monaural air conduction stimuli were assessed using repeated measures analyses of variance in an initial group of 17 participants. The optimal stimulus and recording parameters obtained in the initial group were used subsequently to obtain oVEMPs from 30 additional participants. RESULTS: The effects of stimulus frequency, stimulus level, gaze elevation, and electrode location on the response prevalence, amplitude, and latency of the oVEMP for monaural air conduction stimuli were significant. The maximum N1-P1 amplitude and response prevalence were obtained for contralateral oVEMPs using a 500 Hz tone burst presented at 125 dB peak SPL during upward gaze at an elevation of 30°. CONCLUSIONS: The optimal stimulus and recording parameters quantified in this study were used to establish normative data that may be useful for the clinical application of the air conduction oVEMP.

Normative data for the subjective visual vertical test during centrifugation.

BACKGROUND: The otoliths act as gravito-inertial force sensors and contribute to the perception of spatial orientation. The perception of gravitational vertical can be assessed by asking a subject to adjust a light bar to the vertical. Prior to clinical use of the SVV (subjective visual vertical) test, normative data and test-retest reliability must be established. PURPOSE: To obtain normative data and d etermine the test-retest reliability for the SVV test performed in static and dynamic test conditions. RESEARCH DESIGN: A descriptive design was used to obtain normative data. STUDY SAMPLE: Twenty-four young adults with no history of neurological disease, middle-ear pathology, open or closed head injury, cervical injury, or audiovestibular disorder participated in the study. DATA COLLECTION AND ANALYSIS: The SVV angle was measured in the static position and in three dynamic conditions: (1) on-axis clockwise (CW) rotation, (2) off-axis CW rotation of right ear, and (3) off-axis CW rotation of left ear. RESULTS: In young healthy individuals, the SVV was <2° for static and on-axis rotation, and shifted up to 11° during unilateral centrifugation. Test-retest reliability of the SVV was good for all test conditions. CONCLUSIONS: The normative data obtained in this study may be useful in identifying patients with chronic utricular dysfunction. We recommend the use of difference angles (on-axis SVV - off-axis SVV) to remove baseline bias and decrease the variability of the SVV angles for the off-axis conditions.

Head injury and blast exposure: vestibular consequences.

Young adults are more likely to suffer blast injury and traumatic brain injury (TBI) than other age groups. This article reviews the literature on the vestibular consequences of blast exposure and TBI and concussion. In addition, the vestibular test findings obtained from 31 veterans with a history of blast exposure and/or mild TBI are presented. The authors discuss loss of horizontal semicircular canal function and postural instability related to head injury. Preliminary data suggest the novel theory that otolith organs are uniquely vulnerable to head injury and blast exposure.

The effect of age on the vestibular evoked myogenic potential and sternocleidomastoid muscle tonic electromyogram level.

OBJECTIVE: Cervical vestibular evoked myogenic potentials (cVEMPs) are short-latency electromyogram (EMG) evoked by high-level acoustic stimuli recorded from the activated sternocleidomastoid muscle and used to evaluate otolith organ function. The purpose of this study was to investigate the effects of aging on the cVEMP and on the sternocleidomastoid muscle EMG level. DESIGN: A cross-sectional observational study was used to investigate differences in cVEMP and sternocleidomastoid muscle EMG level in a group of 24 younger and 24 older individuals. cVEMPs were recorded during activation of the sternocleidomastoid muscle at target EMG levels ranging from 0 to 90 µV and during maximum voluntary contraction of the sternocleidomastoid muscle. RESULTS: The sternocleidomastoid muscle EMG amplitude increased as a function of target EMG level for both age groups; however, the mean EMG amplitude was greater for the younger group than the older group, and the variability of EMG amplitude was greater for the older group. The EMG amplitude at maximum voluntary contraction ranged from 88 to 279 µV for the younger subjects and from 32 to 230 µV for the older subjects, and the mean EMG amplitude at maximum voluntary contraction was significantly greater for the younger group than the older group. The cVEMP amplitude increased as a function of EMG target level for each age group. Although cVEMP amplitude increased as a function of target EMG level for both groups, the older group exhibited smaller cVEMP amplitudes, overall, compared with the younger group. To separate the influence of EMG level from aging on cVEMP amplitude, only the responses obtained at the 30 µV target EMG level were considered for the statistical analysis because there was no significant difference in EMG level between groups at the 30 µV target level. The mean cVEMP amplitudes at the 30 µV target level were 101 and 51 µV for the younger and older groups, respectively, and a statistical analysis indicated that cVEMP amplitude for the younger group was significantly greater than the older group. CONCLUSIONS: The findings suggest that the decrement in cVEMP amplitude is related to both age-related changes in the vestibular system and age-related changes in the sternocleidomastoid muscle.