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Abstract:
Three callosotomy patients and aged-matched controls drew
circles bimanually, with the two hands moving in a mirror symmetric
mode or asymmetric mode (i.e., both clockwise or counterclockwise)
at preferred and maximal rates. Similar to previous studies, the
asymmetric mode was less stable for the controls: the trajectories
were more variable, cycle times were slower during maximal rate
performance, and phase transitions were only observed under the
asymmetric mode. In contrast, the callosotomy patients showed no
increase in cycle time in the asymmetric mode and the produced
shape of the circles were similar for the two modes. For the
patients, phase transitions were found in both conditions
indicating similar stability across both coordination modes.
Surprisingly, the patients exhibited a preference for the
asymmetric mode when they were allowed to freely choose a movement
mode. The temporal synchronization between the hands was much
tighter in the aged-matched controls than in the callosotomy
patients. These results argue that in the production of continuous
spatio-temporal movement patterns, interhemispheric transmission
via the corpus callosum significantly contributes to the
synchronization of the movements and to the greater stability of
symmetric movements.
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