Interzonal transcallosal connections of the auditory and parietal cortex.

Transcallosal evoked potentials arising in the parietal region in response to stimulation of the auditory cortex of the opposite hemisphere were investigated in acute experiments on cats immobilized by tubocurarine. Interzonal transcallosal responses were recorded over the whole surface of the parietal cortex and were of two types: positive-negative and negative-positive. Positive-negative EP have a longer response latency and a greater total amplitude of both components. Negative-positive EP disappeared after division of the corpus callosum, whereas positive-negative responses were not significantly changed. Interzonal transcallosal potentials were characterized by the presence of functional interhemispheric asymmetry of individual shape. The right hemisphere was dominant with respect to average amplitude of the negative phase in negative-positive responses. The amplitude of the early positive component was greater in the right hemisphere in males and in the left hemisphere in females. The late negative wave in animals of both sexes was greater in the right hemisphere. Late components of the EP had a significantly shorter peak latency in the dominant hemisphere. Characteristics of generation and interhemispheric asymmetry of auditory-parietal transcallosal responses are discussed and compared with visual-parietal responses.