Somatosensory evoked potential peak latencies and amplitudes in contralateral and ipsilateral hemispheres in normal and severely traumatized brain-injured subjects.

The purpose of this study was to compare in normal and traumatic brain injury (TBI) subjects long latency cortical brain-evoked potential patterns obtained upon stimulation of the median nerves. Quantitative data were analysed involving nine peak latencies and eight amplitudes obtained simultaneously contralaterally and ipsilaterally. Left-right hemispheric differences were also analysed. The following was found: TBI latencies were significantly longer for five of nine peaks (N30, P40, N60, P185, P285). TBI amplitudes were significantly smaller for two of eight amplitudes (P185-N240 and N240-P285). A significant contralateral-ipsilateral latency difference occurred only at P40 where latencies in the contralateral hemisphere are shorter for both normals and TBIs. Significant contralateral-ipsilateral amplitude differences occurred in the four early amplitudes (N30-P40, P40-N60, N60-P105, P105-N140) with amplitudes being smaller on the ipsilateral side. A differential effect, however, was found for amplitudes N30-P40 and P40-N60 where the difference is significantly larger in the contralateral hemisphere for normals but not for TBIs. This suggests that contralateral-ipsilateral amplitude difference can be a marker of extent and severity of injury and may also be helpful in localizing site of injury, particularly interhemispheric or corpus callosal injury. The differential latency and amplitude responses for later peaks occurring in the P300 region suggest sensitivity to detecting impairments in pre-cognitive and early cognitive activities.