Interhemispheric motor coordination

This chapter deals with (a) motor interhemispheric exchanges (transfer of learning), (b) visuo-motor interhemispheric exchanges (Poffenberger's paradigm), (c) bimanual motor coordination, and (d) auditivo-motor coordination. At a behavioral level, studies in transfer of motor learning show an asymmetry in favour of the left hand (following a right hand learning) in right-hander. Poffenberger's paradigm suggests that interhemispheric transfer can occur at several sites. Studies on bimanual coordination systematically report that the functional temporal coupling of homologous muscles is more stable than the coupling of non homologous muscles. Finally, as far as the auditivo-motor coordination is concerned, the behavior is more stable when the response is synchronized, as opposed to syncopated, with the stimulus. At the level of the cerebral activities, motor interhemispheric exchanges in the Poffenberger's paradigm involve frontal motor areas. Bimanual movements are associated with bilateral activation of primary sensorimotor structures, with the same intensity as for unilateral movements. Additionally, they involve median motor areas whose level of activity appears equal or superior to the one observed in unimanual activities. Some of the processes required in order to synchronize bimanual movements could be lateralized in the dominant hemisphere, the time lag observed between hands corresponding to the callosal transmission time. The functional coupling of non homologous muscles is characterized by an increase in cerebral activity, not only limited to the median motor areas but spreading to the right premotor cortex and, bilaterally, to the sensorimotor cortices. Finally, the syncopated auditivo-motor coordination involves a higher level of cerebral activities than the synchronized one.