Basal Ganglia Neural Coding of Natural Action Sequences

In this study we present evidence that neurones in the basal ganglia code the serial order of syntactic (rule-driven) sequences of natural motor behaviour (rodent grooming). Neuronal activity was recorded from the striatum in freely behaving rats while they spontaneously groomed themselves. Offline, we analysed sequential patterns of movement in a frame-by-frame scan of video taped behaviour and evaluated the correlation of neuronal activity to syntactic and nonsyntactic grooming movements. We found that sequential patterns of grooming movements activated striatal neurones. Neurones were activated preferentially during particular serial patterns (syntactic chains) of grooming and were inactive, weaker or different during the same movements in other sequences. Syntactic chains of grooming were preferentially coded by neurones in a dorsolateral striatum site where lesions disrupt syntactic grooming patterns1,13. The timing of neuronal activation, which was generally synchronised with or followed movement onset, suggested a role in the execution of the behavioural sequence rather than one of related to the initiation of phasic elements. We conclude that that neuronal activity in rodent neostriatum codes the serial order of natural actions and not the simple motor properties of constituent actions within a sequence.