Motor sequence chunking is impaired by basal ganglia stroke.

Our main aim was to determine whether individuals with stroke that affected the basal ganglia, organized movement sequences into chunks in the same fashion as neurologically intact individuals. To address this question, we compared motor response times during the performance of repeated sequences that were learned, and thus may be planned in advance, with random sequences where there is minimal if any advance preparation or organization of responses. The pattern of responses illustrated that, after basal ganglia stroke, individuals do not chunk elements of the repeated sequence into functional sub-sequences of movement to the same extent as neurologically intact age-matched people. Limited chunking of learned movements after stroke may explain past findings that show overall slower responses even when sequences of action are learned by this population. Further, our data in combination with other work, suggest that chunking may be a function of the basal ganglia.