Air-conduction auditory steady-state response: comparison of interchannel recording using two modulation frequencies.

BACKGROUND

Two-channel auditory steady-state response (ASSR) recording at high and low MF (modulation frequency) most likely provides an insight about the response amplitude and latency from different directions at the brainstem level and at the thalamus or cortical level. Little is known about the combined relationship between MF (39 and 79 Hz) and electrode montages (ipsilateral and contralateral) to single AM (amplitude modulation) tones on the ASSR amplitude and latency.

PURPOSE

To determine if ipsilateral versus contralateral response asymmetries are present at the brainstem level (79 Hz ASSR) and at the thalamus or cortical levels (39 Hz ASSR).

RESEARCH DESIGN

Descriptive and inferential statistics for interchannel ipsilateral and contralateral ASSR amplitude and latency to 79 and 39 Hz.

STUDY SAMPLE

Twenty-five normal-hearing, right-handed young female adults participated in the study. All participants were right-handed, and their age ranged between 18 to 28 years (mean 24.5 +/- 1.6 years).

DATA COLLECTION AND ANALYSIS

Ipsilateral and contralateral ASSR to 39 and 79 Hz MF and 100% AM stimuli were recorded at 500, 2000, and 4000 Hz carrier frequencies at 65 dB SPL. The ASSR amplitudes and phases were determined for each MF across Fc (carrier frequency) for the two channels to the test (right) ear. ASSR amplitude and latency between recording montages for each MF and across carrier frequency were compared by computing two-way repeated measures ANOVA.

RESULTS

The mean ipsilateral ASSR amplitudes to 39 Hz across frequency were slightly larger (228.6 +/- 61.6 microV) than the contralateral response amplitude (223.2 +/- 78 microV) while the mean ipsilateral 79 Hz amplitudes were smaller (127.3 +/- 114.8) compared to contralateral 79 Hz amplitude (154.6 +/- 112.7 microV). For latency response, the mean ipsilateral/contralateral latency difference, on average, was 1 msec or less for both MFs. Results, in normal female adults, indicated no significant interchannel ASSR asymmetries for amplitude and latency (p > 0.05) at the brainstem (79 Hz ASSR) and at the thalamus or cortical levels (39 Hz ASSR).

CONCLUSIONS

Interchannel ipsilateral and contralateral ASSR amplitude and latency to 79 and 39 Hz are not significantly different in normal, young female adults. Two-channel recording of ASSR to different MFs may be of clinical value in otoneurologic assessment.