The primate basal ganglia and the voluntary control of behaviour

This review summarizes recent experiments on neuronal mechanisms underlying goal-directed behaviour. We investigated two basic processes, the internally triggered initiation of movement and the processing of reward information. Single neurons in the striatum (caudate nucleus, putamen and ventral striatum) were activated a few seconds before self-initiated movements in the absence of external triggering stimuli. Similar activations were observed in the closely connected cortical supplementary motor area, suggesting that these activations might evolve through build up in fronto-basal ganglia loops. They may relate to intentional states directed at movements and their outcomes. As a second result, neurons in the striatum were activated in relation to the expectation and detection of rewards. Since rewards constitute important goals of behaviour, these activitations might reflect the evaluation of outcome before the behavioural reaction is executed. Thus neurons in the basal ganglia are involved in individual components of goal-directed behaviour.