Earlier and later components of tone burst evoked myogenic potentials

The aim of this study was to further investigate the response rates, thresholds, latencies and amplitudes of the earlier and later components of tone burst evoked myogenic potentials (TEMPs) in conditions of binaural and monaural stimulation and recordings in a group of normal subjects in response to a 500-Hz tone burst. Each subject underwent simultaneous binaural acoustic stimulation with bilateral recording (B-TEMP) initially, then monaural acoustic stimulation with ipsilateral recording (M-TEMP) on another day. The results showed 100%, 100%, 54%, and 23% response rates for the earlier components of B-TEMPs, when using 105, 95, 85, and 75 dB acoustic stimulation, respectively. It exhibited a significant decrease in the response rate when the stimulus intensity was attenuated from 95 to 75 dB. In addition, no significant difference in the response rate of the earlier components existed between B-TEMPs and M-TEMPs. For the later components of B-TEMPs obtained from 105, 95, 85, and 75 dB acoustic stimulation, the response rates were 85%, 85%, 62%, and 42%, respectively, higher than those of M-TEMPs significantly. Nevertheless, there were no statistical differences in the mean latencies of each peak (p13, n23, n34, and p44) between B-TEMPs and M-TEMPs under similar stimulus intensity. Meanwhile, no significant relationship existed between the stimulus intensity and the latency, regardless of B-TEMPs or M-TEMPs. Comparing the relative amplitudes between B-TEMPs and M-TEMPs, the former displayed significant smaller p13-n23 amplitude, but larger n34-p44 amplitude. However, the mean thresholds for the earlier and later components between B-TEMPs and M-TEMPs did not differ significantly. In conclusion, monaural acoustic stimulation with ipsilateral recording may elicit larger amplitude of the earlier components, whereas binaural acoustic stimulation with bilateral recording evokes higher response rate and larger amplitude of the later components. Although the nerve pathways for both components are different, the thresholds for these potentials do not differ significantly, indicating that both components may, at least in part, share a common origin, but different pathways. © 2004 Elsevier B.V. All rights reserved.