Abstract
Following monoaural stimulation, long latency auditory evoked potentials (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 drawn up in 1967 by Kimura, which assumes that only anatomically prevailing 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 temporal areas by means of interhemispheric commissures. It is this mechanism which may underline the right ear advantage for verbal stimuli and the left ear advantage for melodies observed when administering dichotic 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 agenesia. Our data support the hypothesis that ipsilateral pathways are greatly inhibited by the contralateral pathways, and therefore auditory stimuli can be supposed to reach the contralateral auditory cortex from where they are transferred through the corpus callosum to the ipsilateral auditory cortex.
Sommario
I potenziali evocati acustici a lunga latenza (PEALL) registrati dalle regioni dello scalpo controlaterali al lato stimolato presentano minor latenza e maggiore ampiezza di quelli registrati omolateralmente, in accordo con il modello operazionale proposto nel 1967 dalla Kimura, in base al quale soltanto le vie acustiche crociate sarebbero attive durante l'ascolto dicotico, mentre le vie dirette sarebbero inibite. Lo stimolo acustico dunque raggiungerebbe la corteccia controlaterale e da qui, tramite il corpo calloso, verrebbe inviato nell'area acustica omolaterale. Ciò spiegherebbe perché l'orecchio destro fornisce migliori prestazioni nel riconoscimento di stimoli verbali e quello sinistro nel riconoscimento di sequenze musicali. Nel presente lavoro abbiamo registrato i PEALL in una giovane di 21 anni affetta da epilessia parziale complessa e agenesia del corpo calloso, al fine di verificare tale ipotesi. I nostri risultati sembrano confermare l'ipotesi della Kimura secondo la quale la via acustica ipsilaterale risulta inibita dalla via controlaterale. Lo stimolo acustico raggiungerebbe pertanto la corteccia uditiva controlaterale, donde verrebbe successivamente trasferlto tramite il corpo calloso alla corteccia uditiva ipsilaterale.
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This work was supported by a grant from the Italian Ministry of Education (ministero della Pubblica Istruzione).
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Aiello, I., Sotgiu, S., Sau, G.F. et al. Long latency evoked potentials in a case of corpus callosum agenesia. Ital J Neuro Sci 15, 497–505 (1994). https://doi.org/10.1007/BF02334611
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DOI: https://doi.org/10.1007/BF02334611