Brain-Stem Auditory-Evoked Potentials Recorded Directly From Human Brain-Stem and Thalamus

Abstract

Brain-stem auditory-evoked potentials were recorded in neurosurgical patients from surface electrodes applied to the VIIIth nerve, medulla, pons, midbrain and cortex; from depth electrodes in the thalamus; and from a movable electrode in the IVth, IIIrd, and lateral ventricles. The potentials recordable over the scalp within 10 ms after click stimulation are characterized by a slow positive wave (peaking at 5 to 6 ms) and a negative wave (8 to 10 ms) with 7 small positive wavelets superimposed upon them. The sources of these components have been identified by observing their increased amplitude in depth recordings, and by tracing the potentials from their intracranial maxima to the scalp. Wave I is generated within the most distal portion of the VIII nerve; Wave V in the midbrain (inferior colliculus); and Wave VI the medial geniculate body. Both low positive and negative components have their origins in the inferior colliculus. Intracranially-recorded brain-stem auditory-evoked potential showed very rapid changes in amplitude within the brain-stem but only slight changes in the more rostral regions, although their amplitude gradients varied in the different components. They also demonstrated minor but systematic shifts in latency with distance from the potential sources, reflecting a significant overlap of separate potentials. This effect must be taken into account in the interpretation of a 'concurrent' intracranial potential as the source of a far-field surface-recorded potential.

Age-Related Changes in the Relationship Between Auditory Brainstem Responses and Envelope-Following Responses

“…Wave III was correlated strongly with AM frequencies in the 100-500-Hz region, while wave IV and V were correlated with AM frequencies below 100 Hz (Fig. 6), consistent with declining maximal synchronization frequencies as one ascends the auditory pathway (reviewed in Joris et al 2004) and with increasingly more central generators of later ABR waves (Lev and Sohmer 1972;Buchwald and Huang 1975;Hashimoto et al 1981). Multivariate analysis using canonical correlations showed a strong correlation between the click ABR waves and the sensitive AM frequency regions of each channel in the young (Table 1).…”

Neural plasticity following auditory training in children with learning problems

“…Conditioning techniques have also been successful in modifying the receptive fields of the adult dorsal and ventral cochlear nuclei (McIntosh and Gonzalez-Lima, 1993;Woody et al, 1994). If neurophysiologic changes occurred in the brainstem that did not significantly impact processing in the inferior colliculus (believed to be the generator of the post-wave-V negativity which was studied herein (Hashimoto et al, 1981)), the changes would not have been identified in this study. The frequency following response and brainstem responses in noise could be altered by Earobics training and the changes would need to be identified with other testing procedures.…”

Eighth nerve contributions to cat auditory brainstem responses (ABR)

“…However, this disparity in the dimension of the VIII nerve between human and cat is too great to account for the relatively modest difference (approximately 3-fold) in the interval between the initial two vertex positive ABR peaks in the cat, 400/~s, compared to 1100 /~s in man. Even considering the differences in conduction velocities of the VIII nerve in the two species (10 meters/s in cat; 13-25 meters/s in humans (Hashimoto et al, 1981;Moiler et al, 1981;Spire et al, 1982)) will not suffice to account for the relatively small difference in the interval between the first two peaks in the two species. We believe that it is the disparity in length of the myelinated portion of the VIII cranial nerve within the temporal bone that is the major factor contributing to the difference in the interval between the first two vertex positive peaks in man and cat.…”

“…Several studies have demonstrated that wave I of the human ABR is coincident in time with activity of the VIII nerve in the cochlea (Sohmer and Feinmesser, 1967) whereas wave II is coincident in time with activity of the intracranial portion of the VIII nerve lying between the cochlea and the brainstem (Moiler et al, 1981;Spire et al, 1982) or of the VIII nerve within the brainstem (Hashimoto, 1981). Moiler and his associates (1986) reported that the intracranial portion of the nerve in monkey is too short relative to its con-duction velocity to allow the identification of both distal and proximal VIII nerve activities in the far field.…”