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

Martina Manns,Felix Strã¶Ckens

doi:10.3389/fpsyg.2014.00206

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.

Highlights

Vertebrate brains display physiological and anatomical left-right differences, which are related to hemispheric dominances for specific functions
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
SIMILAR BUT DIFFERENT – HOW ONE ENVIROTYPIC FACTOR AFFECTS THE INTERACTION OF BOTTOM-UP AND TOP-DOWN SYSTEMS A close comparison of the two most intensively studied avian models – chickens and pigeons- sheds light onto three aspects of cerebral lateralization: (1) it exemplifies the critical impact of an envirotypic factor for the generation of a lateralized neuronal system whose action is superimposed on endogenous asymmetries

Summary

Martina Manns and Felix Ströckens*

In different species like humans, sheep, or chicken, the right hemisphere is dominant for aspects of social cognition (Brancucci et al, 2009; Corballis, 2009; Daisley et al, 2009; Rosa Salva et al, 2012) as well as spatial processing (Tommasi and Vallortigara, 2001; Vogel et al, 2003; Diekamp et al, 2005; Chiandetti, 2011). Such hemispheric specializations might be related to differences in hemispheric processing style.

Manns and Ströckens

CONCLUSION