Topographical Analysis of Subcortical Vertex-Like Activities Evoked by Ipsi- and Contralateral Multimodal Sensory Stimulation in Man

A topographical analysis of the mesencephalic, thalamic and forebrain vertex-like activities evoked by ipsi- and contralateral somatic (SVA), visual (WA) and auditory stimuli (AVA) was made in patients with electrodes implanted for diagnoses and treatment. Typical SVA, WA and AVA recorded from a nonspecific polysensory system (NSS) were mainly bilateral and with similar latencies. Typical AVA to only contralateral stimuli were frequent at the ventrolateral thalamus and striatum level. In contrast, bilateral VA with different latencies and VA evoked only by ipsilateral stimuli were rare and mainly localized at the edge of the NSS. Within the NSS, typical VA to ipsi- and contralateral stimuli showed different cerebral distribution patterns according to the sensory modality stimulated, i.e. SVA showed amplitudes in response to contralateral stimuli smaller than to ipsilateral stimuli at the mesencephalic level, larger amplitudes in response to contralateral than to ipsilateral stimuli at the thalamic level and had equal amplitudes in response to contralateral and ipsilateral stimuli in the forebrain regions. VVA showed amplitudes in response to contralateral stimuli equal to those in response to ipsilateral stimuli at the mesencephalic, thalamic and forebrain levels. AVA showed amplitudes in response to contralateral stimuli equal to those in response to ipsilateral stimuli at the mesencephalic level, had amplitudes of contralateral responses larger than those of ipsilateral responses at the thalamic level and showed different amplitude com-binations in the forebrain regions.