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.
The impulse activity of 227 neurons of field 5 was investigated in cats trained to complete a movement of the forepaw in response to a stimulus. The discharges of each of them were collected relative to three markers: the presentation of the conditional signal, the raising of the paw from a support, and pressing on a pedal. The reactions associated with the performance of the reflex were recorded in 224 neurons. The majority of the cells reacting to the stimulus generated a pronounced excitatory response even at the beginning of the movement, but were inhibited at the moment of the touching of the pedal. Sixty-seven percent of the neurons whose discharges were collected relative to the raising of the paw reacted prior to the appearance of the EMG response. The parietofrontal neurons were identified on the basis of the presence of an antidromic response to the stimulation of the motor cortex. The changes in the discharge frequency which were associated with the movement significantly more often anticipated the EMG response in the parietofrontal neurons as compared with non-parietofrontal cells (79.0 and 63.3%, respectively). The parietofrontal neurons reacted more actively to the conditional signal, light flashes, acoustic tone, and tactile stimulation as well. Their role in the triggering and unfolding of the program of a voluntary movement is discussed.
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