Interhemispheric influences on sensorimotor neurons

The bilateral nature of the m cells' receptive fields does not depend on the conjugate or homotopic cortex for its existence, nor does the ablation affect the coadunate behavior observable among m cells.

Abstract

The forepaw focus of sensitivity in the pericruciate region of cat cerebrum contains functional cell groups with various differences. Previous studies with intact chloralose-anesthetized cats showed that about one-half of the neurons both in front of and behind the cruciate sulcus have large, bilateral receptive fields (m cells). Of the remaining one-half, all of the postcruciate and about one-half of the precruciate cells have small, contralateral receptive fields (s cells). The remaining precruciate neurons have medium-sized, bilateral receptive fields (sb cells), including both forelimbs. In the present study, 600 neurons were isolated and studied in cats with the symmetrically identical tissue of the opposite hemishere ablated. Interhemispheric influences were assessed; the results were compared with those obtained from intact cats. The s cells were unaffected by the ablation, whereas the sb cells were no longer identifiable. Analysis of the data revealed that the sb cells had been converted into s cells by the ablation. The m cells, while still present and identifiable, showed an altered responsiveness to ipsilatral inputs and behaved as though the ablation had deprived them of a tonic facilitatory input. Thus, the bilateral nature of the m cells' receptive fields does not depend on the conjugate or homotopic cortex for its existence, nor does the ablation affect the coadunate behavior observable among m cells. Neither the pathways of the tonic facilitation nor the origin of the bilaterality of the m cells' receptive fields has yet been determined.