Role of the frontal lobes in suppression of complex reactions in rats and cats

Abstract

1. Unilateral lobotomy in rats at the level of the anterior portion of the corpus striatum leads to an increase in threshold or to disappearance of the suppression response to stimulation of the caudate nucleus. Unilateral lobotomy in cats at the level of the posterior sigmoid gyrus and anterior border of the head of the caudate nucleus leads to the same results. On the unoperated side, the suppressive reaction to caudate stimulation is unaltered. 2. Separation of the olfactory bulb in rats or section in the medial region of the frontal lobes at the level of the anterior sigmoid gyrus in cats has no effect on the suppressive influence of the caudate nuclei. 3. Unilateral total destruction of the posterior half of the caudate nucleus, globus pallidus, amygdala, putamen, claustrum, and adjacent regions of the cortex in rats raises the threshold of the suppression by 66–133% for stimulation of the residual anterior divisions of the caudate nucleus on the side of destruction. Isolated destruction of each of the basal ganglia listed above has no effect on the caudatal suppression in rats. 4. Lower levels of the central nervous system, including the basal ganglia and thalamus, thus play no part in the mechanism of the suppression evoked by stimulation of the caudate nuclei so far as established motor reflexes to distant stimuli in rats and cats are concerned. The frontal lobes play a direct part in the mechanism of this suppressive activity of the caudate nuclei.