Evidence for a role of the caudate nucleus in the sequential organization of behavior

Behavioural effects of the cholinergics carbachol and atropine given by means of telestimulation were studied in small groups of freely moving Java monkeys. The sequential structure of behavior was analyzed by assessing the contribution of the preceding behaviours of the treated monkey and its partners to the subsequent behaviour of the treated monkey, in terms of information-theoretical statistics. Carbachol increased the overall variability of behaviour in the treated monkey, enhanced the dependency between the preceding and subsequent behaviour of the treated monkey, and slightly decreased the dependency between the current behaviour of the treated monkey and the preceding behavior of its partners. Atropine only increased the dependency between the treated monkey's current behaviour and the preceding behaviour of its partners. The morphology of overt behaviour remained unaffected following the chosen treatments. Analysis of changes in the frequencies of behaviours belonging to different motivational categories (maintenance, sex, aggression, submission and affiliation) revealed that, after intracaudate injections, all categories were affected to the same degree; in contrast, amygdala injections only affected the categories 'aggression' and 'submission'. It is concluded that the caudate nucleus establishes the relative priority of intra-individual and inter-individual constraints on the programming of behaviour, thereby providing flexibility in the execution of ongoing behaviour; the caudate nucleus is not primarily involved in motor control, nor in the control of particular categories of behaviour.