Anterior corpus callosum modulates symmetric forelimb movements during spontaneous food handling behavior of rats.

Abstract

Bimanual motor actions, such as threading a needle, require coordination of the movements of each hand according to the state of the other hand. By connecting homologous cortical regions between the two cerebral hemispheres, the corpus callosum is thought to play a key role in such bimanual coordination. However, direct experimental evidence of the contribution of the corpus callosum to natural behaviors requiring bimanual coordination, such as feeding, is lacking. We investigated the hypothesis that the corpus callosum mediates bimanual movements during food-handling behavior. We first traced the forelimb-related components of the motor corpus callosum in Long-Evans rats, and found that the callosal fiber bundle from the forelimb motor areas passes through the anterior part of the corpus callosum. We then confirmed by electrophysiological recordings that blocking the axonal conduction of fibers in the anterior corpus callosum reduced neural transmission between cortical forelimb areas. The causal role of corpus callosum in bimanual coordination was then tested by analyzing forelimb kinematics during object manipulation, before and after blocking axonal conduction in the anterior corpus callosum. We found the frequency of occurrence of symmetric bimanual movements was reduced by inhibition of anterior corpus callosum. In contrast, asymmetric bimanual movement was increased. Our findings suggest that the anterior corpus callosum coordinates the direction of bimanual movement.