Cortical Representation of Bimanual Movements

Abstract

It is well established that the discharge of neurons in primate motor cortex is tuned to the movement direction of the contralateral arm. Interestingly, it has been found that these neurons exhibit a directional tuning to the ipsilateral arm as well and that the preferred directions to both arms tend to be similar. A recent study showed that motor cortex cells are also directionally selective to bimanual movements, but the relationship between the bimanual and unimanual representations remains unclear. To address this issue, we analyzed the responses of motor cortical neurons recorded from two macaque monkeys during unimanual and bimanual reaching movements. We decomposed the bimanual movement representation into contralateral and ipsilateral directionally tuned components. Our major finding is that the movement of the contralateral arm modifies the tuning of the cells to the ipsilateral arm such that: (1) the offset and modulation depth of the tuning are suppressed; and (2) the preferred directions are randomly shifted. Both these effects eliminate the correlation between the contralateral and ipsilateral representations during bimanual movements. We suggest that the modification of the ipsilateral arm representation is caused by the recruitment of local inhibition that conveys callosal inputs during bimanual movements. This hypothesis is supported by the analysis of a model of two motor cortical networks, coupled with sparse random interhemispheric projections that reproduce the main features observed in the data. Finally, we show that the modification of the ipsilateral arm representation reduces the interference between the movements of both arms.

Vision Modulates Corticospinal Suppression in a Functionally Specific Manner during Movement of the Opposite Limb

“…It has been proposed that these are subthreshold during unimanual movements, and recruited during bimanual movements in response to control signals from other brain areas (Rokni et al, 2003). The results of our first experiment promoted the conclusion that, when vision is directed to the inactive limb, inhibitory circuits are engaged during unimanual movements.…”

Observed effector-independent motor learning by observing

“…Electrophysiological studies of reaching in non-human primates may provide a neural basis for effector-independent observational learning. Several studies support the idea that neurons in a number of motor regions of the brain implicated in observation and the mirror system, including primary, premotor cortices and supplementary motor areas, are also involved in coding bimanual movements (Donchin et al 1998(Donchin et al , 2002Rokni et al 2003). Studies using fMRI in humans implicate the mirror neuron system in observation learning and identify commonalities in the neural substrates for physical and observational learning (Calvo-Merino et al 2005;Cross et al 2009).…”

Asymmetric Transfer of Visuomotor Learning between Discrete and Rhythmic Movements

“…For example, partially distinct representation in MI for unimanual and bimanual movements (Donchin et al, 2002;Rokni et al, 2003) would explain why there is only a partial transfer of learning within the same limb across unimanual and bimanual tasks (Nozaki et al, 2006;Nozaki and Scott, 2009). Based on this hypothesis, we tried to clarify the differences in control processes between discrete and rhythmic movements by investigating how motor learning of visual rotation was transferred between them.…”