Functional and structural comparison of visual lateralization in birds – similar but still different

Abstract

Vertebrate brains display physiological and anatomical left-right differences, which are related to hemispheric dominances for specific functions. Functional lateralizations likely rely on structural left-right differences in intra- and interhemispheric connectivity patterns that develop in tight gene-environment interactions. The visual systems of chickens and pigeons show that asymmetrical light stimulation during ontogeny induces a dominance of the left hemisphere for visuomotor control that is paralleled by projection asymmetries within the ascending visual pathways. But structural asymmetries vary essentially between both species concerning the affected pathway (thalamo- vs. tectofugal system), constancy of effects (transient vs. permanent), and the hemisphere receiving stronger bilateral input (right vs. left). These discrepancies suggest that at least two aspects of visual processes are influenced by asymmetric light stimulation: (1) visuomotor dominance develops within the ontogenetically stronger stimulated hemisphere but not necessarily in the one receiving stronger bottom-up input. As a secondary consequence of asymmetrical light experience, lateralized top-down mechanisms play a critical role in the emergence of hemispheric dominance. (2) Ontogenetic light experiences may affect the dominant use of left- and right-hemispheric strategies. Evidences from social and spatial cognition tasks indicate that chickens rely more on a right-hemispheric global strategy whereas pigeons display a dominance of the left hemisphere. Thus, behavioral asymmetries are linked to a stronger bilateral input to the right hemisphere in chickens but to the left one in pigeons. The degree of bilateral visual input may determine the dominant visual processing strategy when redundant encoding is possible. This analysis supports that environmental stimulation affects the balance between hemispheric-specific processing by lateralized interactions of bottom-up and top-down systems.

Anticlockwise or clockwise? A dynamic Perception-Action-Laterality model for directionality bias in visuospatial functioning

“…For example, the factors of reading or scanning direction and traffic rules do not apply for non-human animals. Researchers hypothesized that lateralization of some forms of visual behavior (leftward or rightward directionality bias) can be generated in avian species, such as pigeons and domestic chickens, by exposing the developing embryos to biased prenatal sensory experiences (unilateral light stimulation to one eye just before hatching; Casey & Sleigh, 2001; Manns & Strökens, 2014; Rogers, 1990; Rogers, 1991). Additionally, chicks hatched from eggs incubated in completely dark conditions do not develop any asymmetry in the visual pathways and visual behavior in categorization of food items and in responding to predators (Rogers, 2012).…”

When and Why Did Brains Break Symmetry?

“…In birds, lateralization of some types of visual behaviour is generated by exposing the developing embryos to light just before they hatch (in chicks [50]; in pigeons [51]). Chicks hatched from eggs incubated in the dark lack asymmetry of visual behaviour in categorisation of food items and in responding to predators (summarized in Rogers [12]).…”

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

“…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].…”

“…Broadly speaking, the right hemisphere orchestrates a form of primitive avoidance and wariness while the left-hemisphere complements brain specialization with the control of routine behaviours of feeding and analysis in familiar contexts, counteracting distraction and irrelevant response to novelty credited to the right hemisphere [1,30]. Thus, apparently similar behavioural asymmetries can be generated by different neural asymmetric systems [31,32].…”