[Interrelationship between functional interhemispheric asymmetry and photic stimulus contrast in the visual system of...

Transformation of stimuli contrast in animal visual system was revealed in experiments on cats and rats anaesthetized with Nembutal. With zero contrast, there was an initial functional interhemispheric asymmetry (FIAs) of evoked potentials (EPs) in the fields 17 and 18. Dependence of the initial FIAs on stimulation intensity was defined. The sign of the initial EPs asymmetry was stable in cats (right hemisphere) and unstable in rats. Differences in interdependence between FIAs and contrast were found in both animals. In cats, in a wide range of stimuli contrasts, the sign and value of the interhemispheric asymmetry were stable and close to the initial FIAs; while in rats FIAs value directly depended on stimuli contrast and its sign corresponded to that of the contrast. The role of transcallosal influences in the formation of certain EPs FIAs properties was traced down. The discovered characteristics of contrasts transformation seem to contribute to a more reliable functioning of the visual system.