Functional distinction of perigeniculate and thalamic reticular neurons in the cat

Two types of neurons can be recognized in the region above the lateral geniculate nucleus. One cell type is found in the caudal part of the reticular nucleus of thalamus; these cells are accordingly called reticular neurons. The other cell type is located in the perigeniculate nucleus immediately above lamina A of the lateral geniculate nucleus and in the intermediate zone between the perigeniculate nucleus and the reticular nucleus. These cells are referred to as perigeniculate neurons. Electrical stimulation of the optic tract and the visual cortex typically evokes a short burst of spikes in the perigeniculate neurons, and the excitation has a shorter latency from the cortex (range 1.2-2.5 ms) than from the optic tract (range 1.5-3.1 ms). The perigeniculate neurons are also activated by adequate visual stimuli. In contrast, the reticular neurons are unresponsive to visual stimuli and electrical stimulation of the optic tract but they may respond with a burst of spikes to cortex stimulation with rather long latency (range 2.7-5.5 ms). It is concluded that only perigeniculate neurons qualify as interneurons in the recurrent inhibitory pathway to principal cells in the lateral geniculate nucleus.