CODING OF SERIAL ORDER BY NEOSTRIATAL NEURONS - A NATURAL ACTION APPROACH TO MOVEMENT SEQUENCE

The neostriatum controls behavioral sequencing, or action syntax, as w ell as simpler aspects of movement, Yet the precise nature of the neos triatums role in sequencing remains unclear. Here we used a ''natural action'' approach that combined electrophysiological and neuroethologi cal techniques. We identified neostriatal neurons that code the serial order of natural movement sequences of rats, During grooming behavior , rats emit complex but highly predictable species-specific sequences of movements, termed ''syntactic chains.'' Neuronal activity of 41% of cells in the dorsolateral and ventromedial neostriatum coded the sequ ential pattern of syntactic chains. Only 14% coded simple motor proper ties of grooming movements, Neurons fired preferentially during syntac tic chains compared with similar grooming movements made in different sequential order or to behavioral resting, Sequential coding differed between the dorsolateral and ventromedial neostriatum. Neurons in the dorsolateral site increased firing by 116% during syntactic chains, co mpared with only a 30% increase by neurons in the ventromedial site, a nd dorsolateral neurons showed strongest coding of grooming syntax by several additional criteria. These data demonstrate that neostriatal n eurons code abstract properties of serial order for natural movement a nd support the hypothesis that the dorsolateral neostriatum plays a sp ecial role in implementing action syntax.