A search to possible pathways for later peaks of VEMP and N3 potential

Abstract

The VEMP is an inhibitory potential recorded from the sternocleidomastoid (SCM) muscle in response to loud sounds. There are four peaks in VEMP which have been classified according to their latencies, known as p13, n23, n34, p44.Waves p13-n23 which are saccular in origin possibly and have been studied excessively due to the higher response rate in normals whereas the N34- P44 which are believed to be cochlear origin have been scarcely explored thus ignoring their clinical significance. There is another potential (N3 potential) which is thought to be originated from vestibular system is the negative peak at 3 msec in ABR recording. The aim of the study was to know any relation between the later peaks of VEMP and N3 potential and also to explore the possible routes for generation of these potentials. Two groups of subjects participated in the study. First group of subjects (control group) consisted of subjects in the age range of 16 to 45 years, with normal hearing (N=30) and the second group, (experimental group) consisted of 30 subjects with different configuration of sensorineural hearing loss. The experimental group was further divided into three subgroups based upon their hearing loss. Results revealed that all the four groups were significantly different in terms of presence of later peaks of VEMP. One way ANOVA showed significant difference in all the four groups. Results revealed that occurrence of later peaks of VEMP increased with increase in severity of hearing loss. It was observed that in only 6.7% of the subjects when VEMP was absent N3 potential was also absent. In 40% of the subjects when later peaks of VEMP were present N3 potentials were also present suggesting that there might be some similarity in pathway between later peaks of VEMP and N3 potential. Based on the results and literature available it was felt that there could be three possible pathways for later peaks of VEMP, first via Vestibulo-cochlear anastomosis, second through cochlear afferents and third via Olivocochlear bundle. Similarly for N3 potential there could be two sites of origin first could be vestibular nucleus and other one could be cochlear nucleus.