A direct input from amygdaloid complex to caudate nucleus of the rat

Spontaneous unit activity was recorded from the caudate nucleus in rats anesthetized with urethane. Amygdaloid nucleus stimulation altered the spontaneous activity of 51 units (65% of the population tested); 23 units (29%) showed an increase and 28 (36%) a decrease of discharge rate. Moreover, 25 units (32%) responded to stimulation with stimulus-locked spikes. Post-stimulus time histograms revealed 7 patterns of response to amygdaloid stimulation. In 4 groups of cells, stimulus-locked spikes occurred followed by alteration of spontaneous discharge rate. In another 2 groups there was a change of spontaneous discharge without stimulus-locked spikes and in the final group no effect occurred. The possibility of mono-, oligo-, and polysynaptic connections from amygdaloid nuclear complex to caudate nucleus was discussed. It was suggested that an amygdalofugal connection to basal ganglia may provide a pathway whereby activity of the limbic system may exert a modulatory influence on somatic motor mechanisms.