BEHAVIORAL-RESPONSES INDUCED BY ELECTRICAL-STIMULATION OF THE CAUDATE-NUCLEUS IN FREELY MOVING CATS

The caudate nucleus and adjacent structures of 26 freely moving cats w ere stimulated through multiwire electrodes chronically implanted. Two main effects here observed with trains of pulses of high frequency (1 00 Hz) and short duration (1 s): (1) contralateral head turning and (2 ) arrest reaction, which was associated with crouching and escape beha vior. The responses follow a certain topographic distribution. Head tu rning was elicited with the lowest mean threshold in sites located in the internal two-thirds and caudal region of the caudate nucleus, whil e the arrest reaction was elicited from the ventromedial region of the caudate and adjacent nucleus accumbens. Stimulation of the corpus cal losum and internal capsule produces postural instability, ventral flex ion of the head and flexion of the contralateral limb. The extra-cauda te responses were accompanied by contralateral head turning when the s timulated points were near of the caudate border. Experimental evidenc e suggested that striatal responses were not due to current spread to adjacent structures or to activation of corticofugal fibers. The head rotation was suppressed following interruption of the ipsilateral stri atal outflow by electrolytic lesion of the globus pallidus and adjacen t internal capsule. The chemical lesion of the substantia nigra and th e ventral pallidum produced a significant increase in the stimulation threshold for head turning and arrest reaction, respectively. These re sults suggest a topographic arrangement of the responses evoked by ele ctrical stimulation of the caudate nucleus in the cat, which are media ted by the substantia nigra pars reticulata and the ventral pallidum.