Possible evolutionary origins of cognitive brain lateralization

Despite the substantial literature on the functional architecture of the as ymmetries of the human brain, which has been accumulating for more than 130 years since Dax and Broca's early reports, the biological foundations of c erebral asymmetries are still poorly understood. Recent advances in compara tive cognitive neurosciences have made available new animal models that hav e started to provide unexpected insights into the evolutionary origins and neuronal mechanisms of cerebral asymmetries. Animal model-systems, particul arly those provided by the avian brain, highlight the interrelations of gen etic, hormonal and environmental events to produce neural and behavioural a symmetries. Novel evidences showing that functional and structural laterali zation of the brain is widespread among vertebrates (including fish, reptil es and amphibians) have accumulated rapidly. Perceptual asymmetries, in par ticular, seem to be ubiquitous in everyday behaviour of most species of ani mals with laterally placed eyes; in organisms with wider binocular overlap (e.g., amphibians), they appear to be retained for initial detection of sti muli in the extreme lateral fields. We speculate that adjustment of head po sition and eye movements may play a similar role in mammals with frontal vi sion as does the choice for right or left lateral visual fields in animals with laterally placed eyes. A first attempt to trace back the origins of br ain asymmetry to early vertebrates is presented, based on the hypothesis th at functional incompatibility between the logical demands associated with v ery basic cognitive functions is central to the phenomenon of cerebral late ralization. (C) 1999 Published by Elsevier Science B.V. All rights reserved .