The role of striatum in the acquisition of instrumental defensive reactions in dogs.

The model of instrumental defensive reflexes, connected with the maintenance of a certain posture, was used in a chronic experiment on dogs. The motor components of "coordinating" and "cognitive" programs of defensive reflexes were analysed before and after stimulation of the head of the caudate nucleus (CNH). Predominantly inhibitory influences of the striatum on the reflexes were demonstrated. The degree of inhibitory effects (inhibition of "coordinating" program or elimination of the defensive reflexes, "caudate stopping") depended on the parameters and time of application of caudate stimuli. Preliminary subthreshold high frequency stimulation of intralaminar thalamic nuclei significantly increased the inhibitory effects elicited by CNH stimulation. It is suggested that the CNH controls the acquisition of motor behavioral tasks. The degree of elimination of caudate inhibitory influences may be determined by the level of activation of nonspecific thalamic nuclei.