Afferent connections of the nucleus posterior thalami in the rat, with some evolutionary and functional considerations.

The afferents to the nucleus posterior thalami were investigated in the rat using the methods of retrograde and anterograde transport of horseradish peroxidase (HRP). The main afferents arise from the following structures: sensorimotor cortex, zona incerta, thalamic ventrobasal complex, pretectum, intermediate and deep layers of the superior colliculus, nucleus suprageniculatus, nucleus ruber and perirubral area, mesencephalic reticular formation, nucleus interstitialis of Cajal, nucleus tegmenti pedunculopontinus, nucleus reticularis pontis, sensorial and spinal tract trigeminal nuclei. There is some confusion about the anatomical localization and appellation of the posterior thalamic region among mammals. In most of them, however, the pattern of afferents to this area appears to be relatively homogeneous. We conclude that the projections to the thalamic posterior nucleus of the rat are similar to those reported in other mammals. This nucleus has been suspected of playing a role in the processing of somaesthetic or visual informations. On the basis of the multimodal nature of its afferents, a specific role of this nucleus is excluded. Instead, a non-specific function of modulation or integration is suggested.