Delineation of the striate cortex, and the striate-peristriate projections in the guinea pig.

The size and position of the guinea pig area 17 were determined by transneuronal labeling after intraocular injections of 3H-proline or WGA-HRP. Area 17 occupies a large region of the occipital cortex located between two shallow fissures, the fissura sagittalis lateralis and the lateral groove. Area 17 extends for about 6 mm rostral from the occipital pole of the hemisphere, and encroaches occipitally for more than 1 mm upon the ventromedial surface of the hemisphere; the lateral width is up to 4.5 mm. Single injections of WGA-HRP into area 17 produced eight patches of transported tracer which formed the same general pattern in the peristriate cortex, regardless of the position of the injection within the visual field representation of area 17. Two of these patches were found in anteromedial peristriate cortex; three patches were distributed anterolateral and lateral of area 17; and three patches were located in posterolateral peristriate cortex. For several reasons, each of these patches was interpreted as representing a single striate projection onto a separate peristriate area. Comparison of these results with published findings indicates that the parcellation of the peristriate cortex into a variety of different areas, the pattern formed by these areas around area 17, and their reciprocal connections with area 17 follow a common plan in all hitherto studied terrestrial Old World and New World rodents. Lucifer Yellow injections into striate cells projecting to one of the recipient areas (AM) indicated that the pyramidal cells of this set of striate neurons are characterized by a short apical dendrite, and that the basal dendrites of the layer V pyramidal cells branch more profusely than those of the layer III pyramids.