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

Abstract

1Bimanual motor actions, such as threading a needle, require coordination of the 2 movements of each hand according to the state of the other hand. By connecting 3 homologous cortical regions between the two cerebral hemispheres, the corpus callosum 4 is thought to play a key role in such bimanual coordination. However, direct experimental 5 evidence of the contribution of the corpus callosum to natural behaviors requiring 6 bimanual coordination, such as feeding, is lacking. We investigated the hypothesis that 7 the corpus callosum mediates bimanual movements during food-handling behavior. We 8 first traced the forelimb-related components of the motor corpus callosum in Long-Evans 9 rats, and found that the callosal fiber bundle from the forelimb motor areas passes through 10 the anterior part of the corpus callosum. We then confirmed by electrophysiological 11 recordings that blocking the axonal conduction of fibers in the anterior corpus callosum 12 reduced neural transmission between cortical forelimb areas. The causal role of corpus 13 callosum in bimanual coordination was then tested by analyzing forelimb kinematics 14 during object manipulation, before and after blocking axonal conduction in the anterior 15 corpus callosum. We found the frequency of occurrence of symmetric bimanual 16 movements was reduced by inhibition of anterior corpus callosum. In contrast, 17 asymmetric bimanual movement was increased. Our findings suggest that the anterior 18 corpus callosum coordinates the direction of bimanual movement. 19