Efferent connections of the pulvinar nucleus in the cat.

Discrete unilateral electrolytic lesions were placed in the pulvinar nucleus of cats using the stereotaxic approach. The pathways of the degenerated fibres and their terminals were traced to the cerebral cortex and to subcortical nuclei by the method of Fink-Heimer (anterograde degeneration). The cortical projection sites of the pulvinar are the following: suprasylvian cortex, lateral cortex, ectosylvian cortex, cingulate gyrus, area postsubicularis and retrosplenial gyrus. However, the bulk of the cortical projections of the pulvinar nucleus were to mid- and posterior gyri of the suprasylvian cortex. In this study subcortical projections of the pulvinar have been seen to terminate in the superior colliculus, pretectal area, and the following thalamic nuclei: posterior, suprageniculate, dorsolateral, posterolateral, reticular, centromedian, centrolateral, parafascicular and dorsomedial. One of the purposes of this study was to explore possible anatomical connections of the pulvinar that might explain its presumed role in the pain mechanisms. The results of the present study, on subcortical connections of the pulvinar, provide a possible anatomical substrate for such a role where connections of the pulvinar to one or more of the thalamic nuclei implicated in pain mechanisms, the reticular, the intralaminar (centromedian, centrolateral and parafascicular) and the posterior could constitute the necessary anatomical pathway or pathways. Furthermore, the extensive projections of the pulvinar to several cortical regions including the cingulate gyrus could represent another means by which the pulvinar might influence cortical and limbic structures which are known to modify pain sensation.