LONG-LATENCY EVOKED-POTENTIALS IN A CASE OF CORPUS-CALLOSUM AGENESIA

Following monoaural stimulation, long latency auditory evoked potentia ls (LLAEPs) recorded from contralateral temporal areas have a shorter latency and larger amplitude than those recorded from the ipsilateral temporal areas. This observation agrees with the operational model dra wn up in 1967 by Kimura, which assumes that only anatomically prevaili ng crossed auditory pathways are active during dichotic hearing, while direct pathways are inhibited. The inputs may then be conveyed to the contralateral cortex, from where they finally reach the ipsilateral t emporal areas by means of interhemispheric commissures. It is this mec hanism which may underline the right ear advantage for verbal stimuli and the left ear advantage for melodies observed when administering di chotic listening tasks. With the aim of verifying this hypothesis, we recorded temporal LLAEPs in a 21 year-old woman suffering from complex partial seizures, whose CT scan and MRI showed corpus callosum agenes ia. Our data support the hypothesis that ipsilateral pathways are grea tly inhibited by the contralateral pathways, and; therefore auditory s timuli can be supposed to reach the contralateral auditory cortex from where they are transferred through the corpus callosum to the ipsilat eral auditory cortex.