The synaptic organization of the cortical projection to the pulvinar of the squirrel monkey.

Abstract

AbstractThe synaptic morphology of the pulvinar has been examined following cortical lesions in peristriate, posterior temporal and posterior parietal areas. Light‐microscopic stains demonstrate orthograde degeneration in p. lateralis, p. inferior, and the posterior nucleus, with a convergent input to the medial one‐half of p. inferior and the posterior nucleus. Electron microscopic examination shows that parts of two different populations of synaptic terminals degenerate as a result of the cortical lesions: the RS terminal, which rapidly becomes electron‐dense and later is phagocytosed, and the RL terminal, which initially exhibits signs of neurofilamentous hyperplasia and later becomes electron‐dense.Comparisons are made between the pulvinar and other thalamic nuclei with respect to synaptic organization and the origin of extrinsic synaptic terminals. It is pointed out that while the overall arrangements within the pulvinar are equivalent to those in VB, MGB or dLGN, the fact that two different populations of synaptic terminals originate in the cortex suggests functional differences between the pulvinar and other parts of the thalamus examined thus far. The possible phylogenetic origins of different parts of the pulvinar are also discussed.