Multiple projection of the visual field to the medial portion of the dorsal lateral geniculate nucleus and the adjacent nuclei of the thalamus of the cat

The organization in the cat of the projection of the visual field onto the medial part of the central half of dorsal lateral geniculate nucleus (LGNd), the medial interlaminar nucleus (MIN) and the posterior nucleus of the thalamus (PN) has been studied by systematically plotting the receptive fields of single units isolated in the nuclei by tungsten microelectrodes. Using a grid of verticals (azimuth) and horizontals (elevation), projection maps were prepared by locating the recording sites of the units in serial histological sections. We have plotted three separate but related topographical projections of the visual field, one in each nucleus. Particular attention was paid to the projection of the visual axis in the LGNd. With the possible exception of the upper periphery, the whole of the visual field is represented in the MIN, the topographical organization with respect to azimuths being the mirror‐image of that in the LGNd. There were very few binocularly activated units in the MIN and no evidence was found of a laminar segregation of crossed and uncrossed optic tract terminals. The topographical projection onto the PN resembled that in the MIN except that the upper visual field was even more restricted and the organization of azimuth values was again reversed such that the central visual field projected inferomedially and the peripheral field dorsolaterally. In all three nuclei a naso‐temporal overlap was found with receptive fields located across the midline in the ipsilateral hemifield for about 2° in the case of LGNd units and 6° or more in the case of the MIN and PN. Some observations are made on visually active units in the lateral posterior nucleus of the thalamus and the pulvinar, many responding binocularly.