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Cerebellar Activation During Copying Geometrical Shapes

Scott M. Lewis^1,2, Trenton A. Jerde^1,3,4, Charidimos Tzagarakis^1,5, Maria-Alexandra Georgopoulos^1,6, Nikolaos Tsekos^6,7, Bagrat Amirikian^1,5, Seong-Gi Kim^6,7, Kâmil Uurbil^6,7 and Apostolos P. Georgopoulos^1,2,4,5,8

¹ Brain Sciences Center, Minneapolis Veterans Affairs Medical Center, Minneapolis 55417;; ² Department of Neurology, University of Minnesota Medical School, Minneapolis 55455; ³ Graduate Program in Neuroscience, University of Minnesota, Minneapolis 55455; ⁴ Center for Cognitive Sciences, University of Minnesota, Minneapolis 55455; ⁵ Department of Neuroscience, University of Minnesota Medical School, Minneapolis, Minnesota 55455; ⁶ Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota 55455; ⁷ Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota 55455; ⁸ Department of Psychiatry, University of Minnesota Medical School, Minneapolis, Minnesota 55455

Submitted 6 January 2003; accepted in final form 27 April 2003

We studied functional MRI activation in the cerebellum during copying 9 geometrical shapes (equilateral triangle, isosceles triangle, square, diamond, vertical trapezoid, pentagon, hexagon, circle, and vertical lemniscate). Twenty subjects were imaged during 3 consecutive 45-s periods (rest, visual presentation, and copying). First, there was a positive relation between cerebellar activation and the peak speed of individual movements. This effect was strongest in the lateral and posterior ipsilateral cerebellum but it was also present in the paramedian zones of both cerebellar hemispheres and in the vermis. A finer grain analysis of the relations between the time course of the blood oxygenation level–dependent activation and movement parameters revealed a significant relation to hand position and speed but not to acceleration. Second, there was a significant relation between the intensity of voxel activation during visual presentation and the speed of the upcoming movement. The spatial distribution of these voxels was very similar to that of the voxels activated during copying, indicating that the cerebellum might be involved in motor rehearsal, in addition to its role during movement execution. Finally, a factor analysis of the intensity of activated voxels in the ipsilateral cerebellum during copying (adjusted for the speed effect) extracted 3 shape factors. Factor 1 reflected "roundness," factor 2 "upward pointing," and factor 3 "pointing (up or down) and elongation." These results link cerebellar activation to more global, spatial aspects of copying.

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