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.

Manipulating time-to-plan alters patterns of brain activation during the Fitts' task.

Fitts' law predicts that there is an essential trade-off between speed and accuracy during movement. Past investigations of Fitts' law have not characterized whether advance planning of upcoming fast and accurate movements impacts either behavior or patterns of brain activation. With an event-related functional magnetic resonance imaging (fMRI) paradigm, we investigated the neural correlates of advance planning and movement difficulty of rapid, goal-directed aimed movements using a discrete version of the classic Fitts' task. Our behavioral data revealed strong differences in response time, initial movement velocity, and end-point accuracy based on manipulation of both time to plan movements and response difficulty. We discovered a modulation of the neural network associated with executing the Fitts' task that was dependent on the availability of time to plan the upcoming movement and motor difficulty. Specifically, when time to plan for the upcoming movement was available, medial frontal gyrus (BA 10), pre-SMA (BA 6), putamen and cerebellar lobule VI were uniquely active to plan movements. Further, their activation correlated with behavioral measures of movement. In contrast, manipulating movement difficulty invoked a different pattern of brain activations in regions that are known to participate in motor control, including supplementary motor area (BA 6), sensory motor cortex (BA 4, 3, 2) and putamen. Our finding that medial frontal gyrus (BA 10) was important for discrete, fast and accurate movements expands the known role of this brain region, which in the past has been identified as a cognitive processing system supporting stimulus-oriented attending. We now extend this conceptualization to include motor functions such as those employed for processing for rapid, goal-directed aimed movements.