Efferent organization of the cat pulvinar complex, with a note on bilateral claustrocortical and reticulocortical connections

The subcortical inputs to several distinct subdivisions of the cat's visual cortex were examined using retrograde transport of horseradish peroxidase (HRP) with particular reference to the topography of the thalamic projections. Injections along the border between cortical areas 17 and 18 (a representation of the vertical meridian) lead to thalamic labelling in: (1) each lamina of the dorsal division of the lateral geniculate nucleus (LGNd), (2) the medial intralaminar nucleus (NIM), (3) the lateral, medial, and inferior pulvinar nuclei, and (4) the paracentral and central lateral nuclei. A topographic organization was observed in the projections of both the geniculate and pulvinar complexes. The spatial transformations in each system can be characterized as “point-to-line” representations, where points in the visual field are represented by columns (lines) of projection cells. Strikingly similar patterns of retrograde labelling were observed following injections in the medial bank of the middle suprasylvian sulcus (e.g., the Clare-Bishop area, or the posteromedial lateral suprasylvian area (PMLS) of Palmer et al., '78). The thalamic afferents to PMLS differ from those to the 17–18 border, however, in that: (1) the magnocellular laminae of the LGNd (lamina A and A1) do not project to the suprasylvian sulcus, and (2) the suprasylvian projection of the C laminae appears much weaker than their striate-peristriate counterpart. Taken together, the results support the interpretation of Updyke ('77), who, based on observations of the thalamic projections of areas 17, 18, and 19, suggested that the lateral pulvinar and the adjacent striate-recipient zone of the medial pulvinar contain mirror-symmetric representations of the visual field. It is further demonstrated that, the colliculorecipient zone of the medial pulvinar (adjacent to the medial border of the striate-recipient zone) projects to a newly discovered visual area located on the lateral bank of the middle suprasylvian sulcus (i.e., the posterolateral lateral suprasylvian area (PLLS) of Palmer et al., '78), and to area 7, an association area located on the convexity of the middle suprasylvian gyrus. Despite the fact that labelled cells in the colliculorecipient zone frequently were distributed in the characteristic columnar pattern, these data failed to demonstrate a topographic organization in this projection. Finally, several extrathalamic afferent sources were also observed. Brainstem afferents to the 17–18 border were identified in one fortuitous case involving a particularly large injection. These reticulocortical projections originate bilaterally from: (1) locus coeruleus, (2) nucleus subcoeruleus, and (3) the dorsal tegmental nucleus. A few additional labelled cells were found in the central superior nucleus and nucleus linearis, both of which lie close to the midline and are part of the raphe system. In addition, labelled cells were consistently found bilaterally in the claustrum, regardless of the site of injection. The possibility that some of these diverse subcortical afferent sources exert nonvisual influences over the visual cortex is discussed.