Cerebellar mediation of the complexity of bimanual compared to unimanual movements J.I. Tracy, PhD; S.S. Faro, MD; F.B. Mohammed, PhD; A.B. Pinus, MS; S.M. Madi, PhD; and J.W. Laskas, BA Article abstract—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 biman- ual 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. NEUROLOGY 2001;57:1862–1869 The coordination of movement, particularly the abil- ity to rapidly conduct successive movements, is one of the hallmarks of cerebellar function. To assess coordination of movement in a patient suspected of having cerebellar dysfunction, pronation/supination of the hands is often used. Babinski termed a deficit on this task “adiadochokinesis.” 1 It has long been associated with the cerebellum, has become part of neurology training, and is routine during the “bed- side” clinical exam as a check of cerebellar func- tion. 2,3 The cerebellar basis for such movements, particularly for its bimanual format where there is increased complexity related to the phase/antiphase coordination of the hands, has not been verified through neuroimaging. Lesion studies have sug- gested that limb movements such as dysdiadochoki- nesis are impaired ipsilateral to the side of the cerebellar lesion and that the lesions are typically hemispheral and lateral in involvement, not deep nuclear. 4-6 Some researchers propose that the cerebellum and basal ganglia make distinct contributions to such tasks. Some suggest that the basal ganglia (caudate, putamen) contribute an efferent motor component to the task related to movement selection and the mus- cles to implement them, whereas the neocerebellum (hemispheres of posterior lobe, cerebellar nuclei, and vermis) contributes an afferent sensory component involving the monitoring of outcome and optimizing movement trajectories using sensory feedback. 7 Other investigators have found both the basal gan- glia and the cerebellar structures are involved in motor learning but that basal ganglia structures ex- ert more influence on energizing/speeding access of information and the cerebellum with timing and or- dering movements. 8,9 Other brain regions need to be considered in un- derstanding the structures that mediate increased complexity during hand movements. A multifocal, modular view 10 proposes that the frontal lobes are involved with goal development, parietal cortex with spatial representation and planning, premotor/sup- plementary motor areas with movement selection, cerebellum with temporal patterning, and basal gan- glia with switching between movements. The in- volvement of premotor, motor, and supplementary motor areas in the cortex has also been noted for sequential motor tasks, 11 particularly when the movements are bilateral and present greater motor coordination demands. Complex compared with sim- ple finger movements have been found to invoke con- tralateral supplementary motor areas and ipsilateral From the Departments of Neurology and Radiology (Drs. Tracy and Madi), Jefferson Medical College, Thomas Jefferson University; Department of Radiology (Drs. Faro and Mohammed, and A. Pinus), MCP Hahnemann University School of Medicine, Philadelphia; and Ursinus College (J. Laskas), Collegeville, PA. Supported in part by a grant from the National Alliance for Research on Schizophrenia and Depression to J.I.T. Received May 5, 2001. Accepted in final form July 31, 2001. Address correspondence and reprint requests to Dr. J.I. Tracy, Departments of Neurology and Radiology, Jefferson Medical College, Thomas Jefferson University, 111 S. 11 Street, Philadelphia, PA 19107; e-mail: joseph.tracy@mail.tju.edu 1862 Copyright © 2001 by AAN Enterprises, Inc.