CORTICAL VISUAL AREAS OF SHEEP

A stereotaxic method for the sheep brain is described. At its widest part the primary visual area (Visual I) of each hemisphere extended approximately 20 mm anteroposteriorly and, when unfolded, approximately 35 mm from side to side. It occupied both walls of the lateral sulcus, and extended medially to the medial wall of the hemisphere and to the depth of the ectolateral sulcus laterally. The most lateral part of the primary visual area included 10-15.degree. of the ipsilateral field; the contralateral field was represented to 135.degree. from the mid line. Visual II also included a strip of ipsilateral representation on its medial edge and extended to the supra-sylvian sulcus on the lateral surface of the brain. The furthest lateral representation recorded was 130.degree. lateral. Most of both visual areas was concerned with the area centralis and the visual streak. The remainder of the retina had very little cortical representation. Most cells in Visual I were simple with orientational and sometimes directional sensitivity. Some complex and hypercomplex cells were seen in Visual I, and these predominated in Visual II. Receptive field sizes from 0.25-10.degree. were found. Within 15.degree. of the vertical meridian, binocular cells were common in both Visual I and II.