Modular organization of ON and OFF responses in the cat lateral geniculate nucleus

Multiunit mapping techniques were used to investigate whether or not units with ON- and OFF-center receptive fields occur in an orderly arrangement in the cat lateral geniculate nucleus. In the A layers, ON- and OFF-center sites were partially segregated in the dimension parallel to the laminae, with ON-center sites predominant at the dorsal surface of each layer and OFF-center sites relatively more numerous at the ventral surface of the layer. Microelectrode tracks were placed to traverse the visual field map in the nucleus parallel to projection lines, parallel to isoelevation lines and parallel to isoazimuth lines. The tracks placed parallel to projection lines contained long sequences of units of the same center sign, providing evidence that ON and OFF zones are organized in vertical modules which span much or all of the thickness of a layer. The tracks placed parallel to isoelevation and isoazimuth lines contained alternating clusters of ON- and OFF-center sites. These clusters were larger in the dimension representing isoelevation than in the dimension representing isoazimuth. Taken together, these results indicate that the cat lateral geniculate nucleus contains ON and OFF modules oriented perpendicular to the layers.