Specificity and Fluidity of Neural Processing in Perceptual-Motor Skill Learning

Expert performance of complex motor skills requires the learning of a sequence of precisely timed movements. In this dissertation, findings using a novel task that was designed specifically to require the learning of timing between movements while making precisely timed interception responses are described. In the Serial Interception Sequence Learning (SISL) task, participants must make a precisely timed response when a scrolling visual cue is within one of four stationary targets zones, and multiple cues are scrolling onscreen at any one time so that multiple responses can be planned ahead of time. Implicit learning of a practiced sequence is demonstrated by a decrease in performance (number of correct trials) when switching to a random or novel sequence. If either the order or timing components of a trained sequence are selectively altered, performance drops to baseline levels, indicating that order and timing are integrated when the sequence is learned under implicit conditions, aligning with the generalization that implicit knowledge is highly context-dependent and inflexible. The neural correlates of sequence learning in the SISL task are a decrease in activity in a distributed cortical network (visual, parietal, and premotor cortices), likely reflecting more fluid processing in taskrelevant brain regions as perceptual-motor processing becomes more efficient, accompanied by increased activity in the ventral striatum and medial prefrontal cortex. These activations in dopaminergic targets suggest the involvement of dopamine-modulated reinforcement learning within corticostriatal circuits. Patients with mild cognitive impairment (MCI) show preserved sequence learning in the SISL task, whereas those diagnosed with Parkinson's disease (PD) are impaired as a group. Altogether, these results suggest that during perceptual-motor skill learning (where precise timing is essential), corticostriatal dopaminergic reinforcement learning integrates timing and order information into motor programs and leads to decreased activation in task-relevant cortical areas. As a result of learning, behavioral performance is more accurate and neural processing is more fluid in task-relevant areas of the cortex that are part of these corticostriatal circuits.