Neuronal Coding of Serial Order: Syntax of Grooming in the Neostriatum

How does the brain create rule-governed sequences of behavior? An answer to this question may come from a surprising source: the neostriatum (caudate nucleus and putamen). Traditionally, the neostriatum has been considered part of the brain's motor system, but its contribution to the preparation or execution of movement is recognized generally to concern high-level motor functions. Recent work implicates the neostriatum in disorders of sequential action and thought, as in the repetition of thoughts or habits in human obsessive-compulsive disorder and movements or speech in Tourette's syndrome. Yet there is no direct evidence to support the idea that the neostriatum controls sequences of behavior. Using ethological and neurophysiological techniques to study neural activity in the rat neostriatum during syntactic grooming sequences, we found that neuronal activity in the anterolateral neostriatum depended on the execution of syntactic sequences of grooming actions. The individual grooming movements themselves did not activate the neostriatum; activation was determined by the syntactic sequence in which grooming movements were performed. These data provide the first direct evidence that the neostriatum coordinates the control of rule-governed behavioral sequences.