MOTOR CO-ORDINATION AND HAND PREFERENCE AFTER LESIONS OF THE VISUAL PATHWAY AND CORPUS CALLOSUM

Abstract

A MESSAGE presented to one half of the brain may evoke a motor' response governed by either cerebral hemisphere. One might expect that in the intact brain, the hemisphere directly receiving sensory stimuli would be the one which evokes the resulting motor response. Thus, Kliiver (1937) and others (Settlage 1939, Cowey and Weiskrantz 1963) found that after occipital, lobectomy, monkeys would preferentially use the ipsilateral hand. Ettlinger (1961) noted the same change after optic tract section. On the other hand, Downer (1959) found that monkeys did not change their hand preference when responding to a visual cue after restriction of direct visual input to one hemisphere. When one striate cortex was deprived of sensory input by midsagittal section of the optic chiasm and unilateral eye closure, each hand was used with equal facility and undiminished frequency. Similar experiments by Trevarthen (1965a) confirmed these findings. If the corpus callosum was also divided, definite changes occurred. The animals now preferred to reach for food with the hand contralateral to the open eye. The other hand was noted to be awkward but gradually improved with training. Since this did not occur if either the optic chiasm or the callosum was spared, it was inferred that this effect was dependent upon isolation of the motor cortex of one side from the visual cortex receiving the sensory input. These observations did not remain undisputed. Myers, Sperry and