Subcortical locus of temporal coupling in the bimanual movements of a callosotomy patient

The timing of repetitive movements was assessed in a callosotomy patient un der unimanual and bimanual conditions. Similar to neurologically healthy in dividuals, the patient exhibited strong temporal coupling in the bimanual c ondition. Moreover, for both the left and right hands, within-hand temporal variability was reduced in the bimanual condition compared to the unimanua l conditions. This bimanual advantage is hypothesized to reflect the tempor al integration of separable timing signals, one associated with the left ha nd and one associated with the right hand (Helmuth, L. L., & Ivry, R. B. (1 996). When two hands are better than one: Reduced timing variability during bimanual movements. Journal of Experimental Psychology. Human Perception a nd Performance, 2, 278-293). The fact that it persists following callosotom y is inconsistent with models that attribute bimanual coordination in these patients to the control of a single hemisphere. Rather, the results sugges t that motor commands from the two hemispheres are integrated subcortically . (C) 1999 Elsevier Science B.V. All rights reserved.