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

Abstract

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.

Early- and Late-Light Embryonic Stimulation Modulates Similarly Chicks’ Ability to Filter out Distractors

“…Conversely, Di-chicks, hatched from eggs maintained for the whole developmental period in complete darkness, were significantly attracted by the novel elements and could not restrain from pecking at these items before reaching the target, and especially at those placed on their left side. Note that the procedure used here matches the one used in our previous work [33], where we showed a specific effect of light stimulation on hemispheres' functionality with no detriment of dark incubation condition on a typical motor and cognitive development (see also [36] for comparable results on pigeons).…”

“…Light seems to operate on a genetically determined asymmetry by mediating a better cooperation between the two hemispheres. The asymmetrical light stimulation experience does not simply affect hemispheric specialization (like a left-hemispheric dominance of visuomotor control (discussed for instance in [32])) but also how efficiently the hemispheres can interact or cooperate [36,51].…”

Hemispheric Asymmetry in New Neurons in Adulthood Is Associated with Vocal Learning and Auditory Memory

“…However, interhemispheric integration of hemisphere-specific information has been shown to improve visual task performance in pigeons, demonstrating that hemispheric specialization and functional interhemispheric interactions do not require a corpus callosum [77], [78]. In mammals, there is evidence of lateral differences in brainstem auditory processing that do not depend on callosal connections [6].…”

A Matter of Degree: Strength of Brain Asymmetry and Behaviour

“…Interhemispheric communication is more effective in strongly lateralized brains, as found by comparing pigeons hatched from eggs that had received exposure to light with pigeons hatched from eggs incubated in the dark [99]. In a task reliant on use of both hemispheres together, Manns and Römling [99] tested pigeons that had been hatched from eggs either incubated in the dark or exposed to light.…”

“…In a task reliant on use of both hemispheres together, Manns and Römling [99] tested pigeons that had been hatched from eggs either incubated in the dark or exposed to light. The task, known as transitive inference, required monocular training in which one eye was presented with red and blue keys, only the red being rewarded, and then blue versus green keys, only the blue being rewarded.…”