ABSTRACT

One example of a repetitive behavioral sequence is licking in rodents, which is characterized by stereotyped bouts. While the pattern generators are found in the brainstem, basal ganglia (BG) output to the tectum and brainstem nuclei can regulate licking by adjusting the duration of activation of the pattern generators. Another example of a higher-order transition variable controlled by the BG is serial order, the ordering of arbitrary event-level transitions. Acquisition of serial order requires corticostriatal plasticity. Simple transitions can be concatenated to form more complex behavioral sequences by coupling transition controllers. An emergent property of transition control is time. Dopamine depletion and striatal lesions impair interval timing in the seconds-to-minutes range. The repetition control system is crucial for the control of tempo and interval timing. Finally, in the imagination mode, a transition controller may send output to its own input function, making it possible to activate perceptual representations without generating overt behavior. It can be implemented by the reentrant signaling from BG outputs that mainly change the state of the thalamocortical network.