Quantitative investigations of visual brain structures in wild and domestic sheep

A cytoarchitectonic subdivision into visual structures and neocortical grey and white matter has been made from frontal serial sections of brains of mouflons (Ovis ammon musimon) and domestic sheep (Ovis ammon f. aries). The reduction rates determined for the volumes of the brain areas are calculated by means of intraspecific allometric methods. The overall decrease of visual brain structures in domestic sheep compared with wild sheep amounts to 25.9%, The greatest reduction is found in the striate area (30.2%), followed by the lateral geniculate body (25.4%), the optic tract (20.6%) and finally the superior colliculus (12.1%). The neocortex as a whole decreases in sheep under domestication by 26.4% in volume. The reduction rate of neocortical grey matter amounts to 24.9%, that of the white matter to 28.9%. The changes of brain size in domestic sheep may be functionally correlated to changes of the environmental conditions which are due to domestication.