Exp Brain Res (2010) 205:375–385 DOI 10.1007/s00221-010-2372-6 123 RESEARCH ARTICLE Movement chunking during sequence learning is a dopamine-dependant process: a study conducted in Parkinson’s disease Pierre-Luc Tremblay · Marc-Andre Bedard · Dominic Langlois · Pierre J. Blanchet · Martin Lemay · Maxime Parent Received: 16 April 2010 / Accepted: 14 July 2010 / Published online: 3 August 2010  Springer-Verlag 2010 Abstract Chunking of single movements into integrated sequences has been described during motor learning, and we have recently demonstrated that this process involves a dopamine-dependant mechanism in animal (Levesque et al. in Exp Brain Res 182:499–508, 2007; Tremblay et al. in Behav Brain Res 198:231–239, 2009). However, there is no such evidence in human. The aim of the present study was to assess this question in Parkinson’s disease (PD), a neuro- logical condition known for its dopamine depletion in the striatum. Eleven PD patients were tested under their usual levodopa medication (ON state), and following a 12-h levo- dopa withdrawal (OFF state). Patients were compared with 12 healthy participants on a motor learning sequencing task, requiring pressing fourteen buttons in the correct order, which was determined by visual stimuli presented on a computer screen. Learning was assessed from three blocks of 20 trials administered successively. Chunks of movements were intrinsically created by each participant during this learning period. Then, the sequence was shuZed according to the participant’s own chunks, generat- ing two new sequences, with either preserved or broken chunks. Those new motor sequences had to be performed separately in a fourth and Wfth blocks of 20 trials. Results showed that execution time improved in every group during the learning period (from blocks 1 to 3). However, while motor chunking occurred in healthy controls and ON-PD patients, it did not in OFF-PD patients. In the shuZing con- ditions, a signiWcant diVerence was seen between the pre- served and the broken chunks conditions for both healthy participants and ON-PD patients, but not for OFF-PD patients. These results suggest that movement chunking during motor sequence learning is a dopamine-dependent process in human. Keywords Parkinson · Dopamine · Striatum · Motor learning · Movement · Sequence learning Introduction Motor sequences are used in simple movements such as reaching and grasping an object as well as more complex skills such as using a tool or playing a music instrument. Learning of such skills is thought to involve the combina- tion or the grouping of single movements into Xuent sequences, leading to coordinated actions (Seidler 2006; Verwey and Eikelboom 2003). According to such a view, motor skill would contain multiple groupings of simpler movements. With practice, those groupings consolidate into chunks, which optimize the automatic execution of movements. Sakai et al. (2003) have demonstrated that diVerent chunks can be created by diVerent persons for a P.-L. Tremblay · M.-A. Bedard (&) · D. Langlois · M. Parent Department of Psychology, Cognitive Pharmacology Research Unit, University of Quebec in Montreal (UQAM), Station Downtown, P.O. Box 8888, Montreal, QC H3C 3P8, Canada e-mail: bedard.marc-andre@uqam.ca P. J. Blanchet André-Barbeau Movement Disorder Centre, CHUM, Montreal, QC, Canada P. J. Blanchet Département de Stomatologie, Faculté de Médecine Dentaire, Université de Montréal, Montreal, QC, Canada M. Lemay Département de kinésiologie, UQAM, Montreal, QC, Canada M. Lemay Centre de Réadaptation Marie-Enfant (CHU Sainte-Justine), Montreal, QC, Canada