Visual Properties of Perigeniculate Neurons in the Cat

Abstract

Interneurons are thought to play an important role in processing visual as well as non-visual information at the level of the lateral geniculate nucleus (LGN). Dubin and Cleland (1977) have distinguished two groups of geniculate interneurons, (i) those within the LGN layers (intrageniculate), and (ii) others in the immediate vicinity of the LGN, dorsal to layer A, in the perigeniculate nucleus, PGN. The neurons in the PGN, like LGN relay cells, are known to receive monosynaptic retinal input (Schmielau, 1979; Schmielau and Roenneberg, 1980) as well as an innervation of recurrent geniculo-cortical fibers (Ahlsen and Lindström, 1978a). In addition there is a cortico-thalamic projection to the PGN (Scheibel and Scheibel, 1966). Neurons of the PGN send an inhibitory projection back into the upper two geniculate layers A and Al (Ahlsen and Lindström, 1978b). The visual properties of PGN neurons are quite distinct from those of geniculate relay cells as has been shown by Sanderson (1971) and Dubin and Cleland (1977). The receptive fields, RF, are larger without a center-surround organization. They show an on/off response to light stimulation and are mainly binocular. PGN neurons also receive non-visual input from the mesencephalon (Ahlsen et al., 1980a and b). They are inhibited by electrical stimulation of the mesencephalic reticular formation (Schmielau, 1979). In addition it has been found that PGN cells respond to the stretching of extrinsic ocular muscles (Donaldson and Dixon, 1980).