Transient peripheral vestibular hypofunction measured with vestibular short-latency evoked potentials following noise exposure in rats.

Exposure to 120 dB sound pressure level (SPL) band-limited noise results in delayed onset latency and reduced vestibular short-latency evoked potential (VsEP) responses. These changes are still present 4 wk after noise overstimulation. Noise-induced hearing loss (NIHL) has been shown to vary in extent and duration based on the noise intensity. This study investigated whether noise-induced peripheral vestibular hypofunction (NPVH) would also decrease in extent and/or duration with less intense noise exposure. In the present study, rats were exposed to a less intense noise (110 dB SPL) but for the same duration (6 h) and frequency range (500-4,000 Hz) as used in previous studies. The VsEP was assessed 1, 3, 7, 14, 21, and 28 days after noise exposure. In contrast to 120 dB SPL noise exposure, the 110 dB SPL noise exposures produced smaller deficits in VsEP responses that fully recovered in 62% (13/21) of animals within 1 wk. These findings suggest that NPVH, a loss or attenuation of VsEP responses with a requirement for elevated stimulus intensity to elicit measurable responses, is similar to NIHL, that is, lower sound levels produce a smaller or transient deficit. These results show that it will be important to determine the extent and duration of vestibular hypofunction for different noise exposure conditions and their impact on balance.NEW & NOTEWORTHY This is the first study to show a temporary noise-induced peripheral vestibular hypofunction that recovers following exposure to continuous noise.

Monothermal Caloric Screening to Improve Healthcare Value.

OBJECTIVES: To evaluate whether monothermal caloric screening can reduce the number of caloric irrigations required in the vestibular testing battery while maintaining diagnostic accuracy. DESIGN: Prospective controlled cohort study. Three hundred and ninety patients referred for vestibular testing at this tertiary referral health system over a 1-year period were evaluated; 24 patients met exclusion or failure criteria and 366 patients were included in the study. Population was 35.6% male; average age was 50.4 years old. Each patient underwent caloric testing using either warm or cool water irrigation initially and this data was used for monothermal screening data. All patients then completed bithermal binaural caloric testing to obtain the "gold standard" bithermal data for comparison. The sensitivity and specificity of monothermal cool or monothermal warm caloric tests were calculated using a receiver operating characteristic curve analysis. RESULTS: Using a monothermal interear difference threshold of 25%, warm monothermal screening had sensitivity of 98.0%, specificity of 91.3%, false negative rate of 2%, and false positive rate of 8.7%. Cool monothermal screening also had excellent sensitivity (92.3%) and specificity (95.3)%, with a false negative rate of 7.7%, and a false positive rate of 4.7%. The diagnosis associated with the single false negative warm monothermal caloric test was compensated vestibular paresis. In the study population, 71.9% had a negative monothermal screen; if the monothermal data were accepted, 2 fewer irrigations would have been performed resulting in an average saving of $264 (typical Medicare reimbursement for 2 irrigations) billed per patient screened as well as shortening the average testing battery by about 15 min. CONCLUSIONS: Warm monothermal caloric screening can reduce time and cost of vestibular testing while nearly matching the diagnostic accuracy of bithermal testing.

Stimulation of otolith irregular fibers produces a rostro-caudal gradient in activity in the vestibular nuclear complex (VNC), but not the vestibulocerebellum (VeCb).

The vestibular system is important for posture, balance, motor control, and spatial orientation. Each of the vestibular end organs have specialized neuroepithelia with both regular and irregular afferents. In otolith organs, the utricle and saccule, afferents most responsive to linear jerk (jerk - derivative of acceleration) are located in the striola and project centrally to the vestibular nuclear complex (VNC) as well as the uvula and nodulus of the vestibulocerebellum (VeCb). The pattern of central neuronal activation attributed to otolith irregular afferents is relatively unknown. To address this gap, c-Fos was used as a marker of neuronal activity to map the distribution of active neurons throughout the rostro-caudal extent of the VNC and VeCb. Immunohistochemistry for c-Fos was performed to assess activation of VNC and VeCb neurons in response to a linear jerk stimulus delivered in the naso-occipital plane. Activated neurons were distributed throughout the VNC, including the lateral vestibular nucleus (LVe), magnocellular medial vestibular nucleus (MVeMC), parvocellular medial vestibular nucleus (MVePC), spinal vestibular nucleus (SpVe), and superior vestibular nucleus (SuVe). Notably, after stimulation, the MVePC exhibited the greatest number of c-Fos labeled nuclei. Significant increases in c-Fos labeling were found in mid-rostrocaudal and caudal regions of the VNC in the LVe, MVe, and SpVe. Additionally, c-Fos labeling was observed across all regions of the VeCb after jerk stimulation. Significant increases in the number of labeled nuclei were found throughout the rostro-caudal extent of the nodulus and uvula. However, jerk stimulated increases in activity for the paraflocculus were restricted to the caudal VeCb. The distribution of neuronal activity suggests that regions receiving the greatest direct otolith input exhibit the most substantial changes in response to otolith derived, irregular fiber stimulation. Highlights: Nuclei with descending projections (LVe, MVePC, and SpVe) demonstrated the greatest change in activity after naso-occipital jerk stimulation.Naso-occipital jerk stimulation preferentially activates caudal VNC neuronsNaso-occipital jerk stimulation activates neurons throughout the VeCbJerk stimulation in the naso-occipital plane has the greatest effects on activity in VNC and VeCb regions with the greatest inputs from afferents originating in gravity receptors.