An fMRI study of training voluntary smooth circular eye movements.

Despite a large number of recent studies, the promise of fMRI methods to produce valuable insights into motor skill learning has been restricted to sequence learning paradigms, or manual training paradigms where a relatively advanced capacity for sensory-motor integration and effector coordination already exists. We therefore obtained fMRIs from 16 healthy adults trained in a new paradigm that demanded voluntary smooth circular eye movements without a moving target. This aimed to monitor neural activation during two possible motor learning processes: (a) the smooth pursuit control system develops a new perceptual-motor relationship and successfully becomes involved in voluntary action in which it is not normally involved or (b) the saccadic system normally used for voluntary eye movement and which only exhibits linear action skill develops new dynamic coordinative control capable of smooth circular movement. Participants were able to improve within half an hour, typically demonstrating saccadic movement with progressively reduced amplitudes, which better approximated smooth circular movement. Activity in the inferior premotor cortex was significantly modulated and decreased during the progress of learning. In contrast, activations in dorsal premotor and parietal cortex along the intraparietal sulcus, the supplementary eye field and the anterior cerebellum did not change during training. Thus, the decrease of activity in inferior premotor cortex was critically related to the learning progress in visuospatial eye movement control.