THE PRIMATE STRIATUM - NEURONAL-ACTIVITY IN RELATION TO SPATIAL ATTENTION VERSUS MOTOR PREPARATION

The primate basal ganglia are known to be involved in the initiation a nd control of visually guided movements, However, the precise role of these structures is not clear, partly because most neurophysiological studies have not dissociated neuronal activity related to visuomotor p rocessing from that reflecting other aspects of behaviour, such as shi fts of spatial attention. Moreover, the way the basal ganglia function together with the frontal cortex during movement initiation and execu tion is still a matter of debate, In an effort to clarify these issues , we recorded single neurons from the striatum (caudate nucleus and pu tamen) in two rhesus monkeys trained to perform a conditional visuomot or task, and compared their properties with those of the frontal corte x. The experimental paradigm was designed to distinguish neuronal acti vity associated with shifts of attention from that reflecting motor pr eparation. in a given trial, an identical visual stimulus could serve as a cue for the reorientation of spatial attention or as a cue for es tablishing a motor set depending on when it occurred during that trial . Additional aspects of the paradigm were designed to identify neurons whose activity differed when various stimulus configurations instruct ed the same action (stimulus effect), as well as neurons whose activit y differed when two different actions were instructed by the same stim ulus (movement effect). The majority of cells (60%) were preferentiall y active after instructional cues, 38% discharged preferentially after attentional cues, and the remaining 2% of cells discharged equally af ter both types of cue, Neurons active after instructional cues were fu rther analysed for stimulus and movement effects. During movement prep aration, the activity of the vast majority of striatal cells (putamen, 81%; caudate, 76%) varied significantly when different stimuli instru cted the same action. Likewise, when different movements were instruct ed by the same stimulus, preparatory activity of a majority of cells ( putamen, 92%; caudate, 82%) changed, Consequently, a substantial propo rtion of cells showed combined stimulus and movement effects. Comparis on of these neuronal properties with those of the dorsal premotor cort ex showed significantly higher proportions of cells in the striatum wh ose activity reflected sensory or sensorimotor processing, These resul ts suggest that the basal ganglia are involved in shifting attentional set and in high-order processes of movement initiation, including the linking of sensory information with behavioural responses.