Contralateral visual field representation in area 17 of the cerebral cortex of the agouti: a comparison between the cortical magnification factor and retinal ganglion cell distribution.

The cortical representation of the contralateral visual field in area 17 of the agouti's brain was studied by multiunit recording. The borders of area 17 were determined by electrophysiological, cytoarchitectonic and myeloarchitectonic criteria. The results were plotted in flat, bidimensional representations of the cerebral cortex to minimize perspective distortions. The V1 map, a first order topological transformation of the visual field, shows a magnified representation of the horizontal meridian that corresponds to a retinal specialization, the visual streak. The visual field representation has asymmetries that are not directly related to the topography of the retinal ganglion cell density. Whereas the ganglion cell density shows a plateau along the visual streak, the areal cortical magnification factor is higher in the region that corresponds to the intersection of the horizontal and vertical meridians. This suggests functional specializations that are not obvious when one considers the distribution of the whole ganglion cell population but which might be related to the distribution of specific ganglion cell classes.