Effects of electrical stimulation of the caudate nucleus on functionally identified neurons of the sensorimotor cortex in the cat brain.

Paired stimulation was used to study the effects of the caudate nucleus on the specific and nonspecific responses of projection neurons of the sensorimotor cortex in the cat brain. Caudal influences on the neurons being studied had insignificant effects on specific peripheral evoked responses. Nonspecific peripherally evoked activity was in most cases inhibited by caudate spike activity, and the pattern of evoked activity underwent significant modulation in conditions of a constant type of peripherally evoked response. It is suggested that the caudate nucleus acts as a filter of proprioceptive information in the cortex or in pathways to the cortex: specific corticopetal information is passed unchanged, while nonspecific signals are predominantly inhibited or significantly modulated.

Activity of substantia nigra neurons in the cat brain during a self-initiated behavioral act.

Cats were trained to perform a self-initiated behavioral act in the form of an operant food-obtaining reflex with defined time requirements. Activity was recorded from 50 dopaminergic neurons (identified in terms of their low frequency of background activity and long action potentials) and 67 nondopaminergic neurons of the substantia nigra and adjacent region. Dopaminergic neurons were the more responsive. Prior to EMG activation, the activity of 33 (66%) of these cells changed, and 44 (88%) showed changes in activity on movement. Dopaminergic neurons showed increased activity during the period of waiting for the conditioned stimulus, predicting the release of reinforcement or its absence. These cells were more frequently activated in response to a positive signal and reinforcement and were more frequently inhibited in the absence of reinforcement. The high reactivity of dopaminergic neurons during execution of a movement task could be explained by the involvement of a cognitive component, i.e., determining the point at which the movement should start.

Pre-movement activity of neurons in the parietal associative cortex of the cat during different types of voluntary movement.

Pre-movement activation of electromyographic spike activity of 201 neurons of field 5 was studied in cats trained to carry out a stereotypical act (lifting the anterior footpad to press a pedal) in response to a conditioned stimulus (experimental series 1) and without a conditioned stimulus (self-initiated movement, experimental series 2). In series 1, 69.2% of neurons were activated and 13.5% were inhibited before the movement. Prior changes in activity were also seen in intersignal movements, with activation of 40.6% and inhibition of 21.7% of neurons. The time parameters of excitatory and inhibitory responses in both situations were similar, with pre-movement intervals of 19-1640 msec. In series 2, pre-movement inhibition was seen rather more frequently than activation (36.7% and 33.7% respectively). The earliest changes were inhibitory, occurring some 1800 msec before movements, while excitatory changes occurred only 880 msec before movement. These data indicate the involvement of the parietal associative area in the can not only in executing, but also in preparing for different types of movement, including self-initiated movements, and that inhibition has an active role in this process.