Cerebellar mediation of the complexity of bimanual compared to unimanual movements.

OBJECTIVE: To study rapidly alternating movements under fMRI in order to identify the brain regions that mediate increased complexity in bimanual vs unimanual movements and to verify the localization of a clinical test of limb ataxia (diadochokinesis). METHODS: Unimanual and bimanual movements, that is, palm(s) pronated then supinated, served as stimulation in a block design fMRI investigation at 1.5 T. Analyses compared bimanual movements and rest for each hand separately and the unimanual conditions combined. A pronation/supination task was chosen as it provides the same objective motor output during unimanual and bimanual formats. The increased coordination demand of the bimanual format (phase/antiphase movements) was expected to result in distinct activation in supplementary motor, primary motor, prefrontal, and cerebellar regions. RESULTS: The bimanual task uniquely elicited responses in specific anterior medial and posterior (vermal) cerebellar regions. CONCLUSIONS: The study corroborated clinical use of diadochokinesis tasks to test for aspects of cerebellar integrity. The data do not support the literature emphasizing basal ganglia mediation of this type of coordinated movement. Cerebellar medial and vermal regions (in connection with central nuclei) are proposed as the locus within the cerebellum for mediating complexity, that is, the effective integration of separate limb movements that proceed in an asynchronous but systematic fashion.

A comparison of 'Early' and 'Late' stage brain activation during brief practice of a simple motor task.

This research study addresses the question: does the neural circuit implementing a motor task undergo change as a function of even limited practice? To detect potential neural changes associated with limited practice we compared brain activation at the early and late stages of motor performance on a simple task over one relatively brief session. Single-finger opposition served as cognitive stimulation during collection of BOLD fMRI signal. We predicted prefrontal cortex activation would be prominent early, with basal ganglia activation becoming prominent during late stage performance. Results revealed that both early and late performance involve areas in the cerebellum, prefrontal, mid-temporal, extrastriate, and parietal cortices, but that the particular regions within these broad areas differed for the two points of performance. The strongest dissociation between early and late performance involved the corpus striatum, thalamus, and cingulate gyrus. The findings suggested the neural circuit implementing this simple task varied over a relatively brief window of practice. Implications for defining the neurocognitive function of the structures involved, particularly the cerebellum, are discussed.