Asymmetrical Commissural Control of the Subdominant Hemisphere in Pigeons.

Functional brain asymmetries depend both on hemisphere-specific factors and lateralized commissural interactions, but their detailed neural mechanisms are mostly unknown. Because birds are visually lateralized, we tested pigeons monocularly in a color discrimination task while recording from single visuomotor forebrain neuron. All birds learned faster and responded quickly with the right eye and left hemisphere. This asymmetry depended on three factors. First, Go-stimulus onset resulted in a higher left hemispheric proportion of excited relative to inhibited neurons such that, second, left-sided visuomotor neurons could trigger the animal's response faster. Third, the left hemisphere was able to adjust the timing of individual activity patterns of right hemispheric neurons via asymmetrical commissural interactions, such that the right hemisphere came too late to control the response. These results imply that hemispheric dominance in birds is realized by both lateralized activation of forebrain motor areas and shifts of the contralateral spike time.