The impact of asymmetrical light input on cerebral hemispheric specialization and interhemispheric cooperation.

Hemispheric specialization potentially provides evolutionary advantages by enhancing cognitive capacities. However, separation of function might be advantageous only with the presence of commissural systems allowing for efficient information exchange and cooperation between the hemispheres. Here we investigate hemispheric cooperation in pigeons as they possess an asymmetrically organized visual system that develops in response to biased ontogenetic light stimulation. This allows comparison of the integration capacities of lateralized (light-incubated) and non-lateralized (dark-incubated) animals. We show that pigeons integrate information learnt separately with each hemisphere when confronted with a transitive reasoning task that they cannot solve with the knowledge of one hemisphere alone. Impairments in dark-incubated birds demonstrate that this ability depends on asymmetrical embryonic light stimulation. Our study provides for the first time direct evidence that lateralized environmental experience not only induces hemispheric specialization, but also affects the efficiency of interhemispheric crosstalk. Environmental factors can influence the tight interplay between the hemispheres, which in turn determines cognitive abilities.