Neuronal mechanisms of goal-directed behavior in monkeys.

Abstract

correlates of different forms of behavior that not a single authors has yetundertaken the task of analyzing this enormous material and making as objective an evaluation of it as possible. The main reason for this, inmy view, is not negligence on the part of research workers, but theunbelievable diversity of the technical approaches used for conducting such investigations. In this connection it seems to me to be more productive to limit the task to a brief survey of my own observations and data in the literature on neurophysiological mechanisms of one form of delayed behavior in monkeys. These investigations have now been in progress in our laboratory for about i0 years, and we have used methods of long-term recording of single unit spike discharges in the cerebral cortex and deep brain formations~ Those taking part in these investigations were A. A. Pirogoy,~ A. A. Orlov, V. I. Shefer, A. P. Shutov, S. D. Peskov, and N. P. Kurzina. In addition, the structure of the neuronal and synaptic organization of the brain formations chosen for study has been investigated by G~ P. Dem'yanenko. The principal behavioral model which we used is a simplified food-getting reflex in which the position of the visual stimulus on the screen also indicated'the location of the pedal (or lever) which the animal had to press (or move) in order to obtain food reinforcements. This manipulation corresponds to processes of long-term memory and, consequently, to the rigid links of the behavioral act [6]. Two unstable factors always were included in the program of the investigations: The position of the acting conditioned stimulus and the duration of the delay which followed it were constantly changed. After perceiving the position of the stimulus the animal had to retain the information obtained throughout the period of delay (Short-term, operative memory). This element of the behavioral program, making it highly adaptable to spatiotemporal parameters of the concrete situation, can be classed as a flexible link of the regulatory systems of the brain. Stimulus Information Coding. Processes of coding the main biologically significant component of the program- the conditioned stimulus, which determines the direction of the subsequent motor act, are of fundamental importance here. The characteristics of reflection of the spatial features of the stimuli by the higher integrative systems of the monkey's brain, namely the frontal and parietal zones of the cortex, are of the greatest interest. In the frontal cortex the middle third of the principal sulcus, which is regarded as the locus of short-Cerm spatial memory [9, 20], attracts special attention. If monkeys are trained to perform motor tasks with right and left photic stimuli followed by a delay, it is easy to show that most cells of the frontal cortex are activated by the conditioned stimuli and during realization of the motor act. Japanese workers [22, 24, 25] called these cells visuokinetic, but I prefer to call them spatially selective corticalneurons. Significant differences in the form of the response and the firing rate of these cells have been found depending on the side on which the conditioned stimulus is located. Discrimination of the side of stimulation by neurons is preserved also during the period of delay, i.e., it is a manifestation of processes of short-term spatial memory [2-4, 17, 5].