The visual claustrum of the cat. I. Structure and connections

Abstract

The cat's dorsocaudal claustrum was studied in Golgi preparations, by electron microscopy, and by anterograde and retrograde tracer techniques. It receives a convergent retinotopic projection from several visual cortical ares, including areas 17, 18, 19, 21a and PMLS (posteromedial lateral suprasylvian area). The projection arises from spiny dendrite cells (pyramidal and fusiform) in the middle of cortical layer VI. As shown by a double label experiment, they form a separate population from those projecting to the lateral geniculate nucleus. There are also inputs from the lateral hypothalamus, from the nucleus centralis thalami, and probably from the locus coeruleus, but not from the sensory nuclei of the thalamus. Non-visual cortical areas do not project to the visual claustrum, but many of them are connected to other parts of the nucleus. For example, the splenial (cingulate) gyrus projects to a claustral zone just ventral to the visual area, and regions anterior to the visual area are connected with somatosensory and auditory cortex. The commonest cell type in the claustrum is a large spiny dendrite neuron whose axon leaves the nucleus after giving off local collaterals. Small spine-free cells, with beaded dendrites and a locally arborizing axon, are found also. Electron microscopy of the claustrum after ablation of the visual cortex showed degenerating type 1 axon terminals synapsing on spines and beaded dendrites, suggesting a direct cortical input to both cell types. The visual claustrum projects back to the visual cortex, to the same areas from which it receives an input. The return projection is predominantly ipsilateral, but there is, in addition, a small crossed projection. The claustrocortical axons terminate in all cortical layers but most heavily in layers IV and VI. The majority of the cells in the visual claustrum project to the cortex, and retinotopy is maintained throughout the entire corticoclaustral loop. No subcortical projections from the claustrum could be identified.

An intracellular analysis of geniculo‐cortical connectivity in area 17 of the cat.

“…All layer 6 cells, for example, received direct excitation from geniculate afferents, and therefore so did all cortico-geniculate neurones. Layer 6 also contains cells projecting to the visual claustrum (LeVay & Sherk, 1981). Although these cells were not studied specifically in the present investigation, the uniform monosynaptic excitation of layer 6 cells indicates that they also receive direct excitation from the l.g.n.…”

Termination of afferent axons in macaque striate cortex

“…For example, afferents from pulvinar and extrastriate cortex do not end in layers 4A or 4C (Benevento et al, 1975;Ogren and Hendrickson, 1976;Spatz, 1977;Tigges et al, 1977;Rockland and Pandya, 1981). While the claustrum projects in a topographic fashion to geniculo-recipient laminae, there is no evidence for the precise laminar segregation that characterizes LGN inputs (Carey et al, 1980;LeVay and Sherk, 1981). And the numerous other small nuclei that have known projections to striate cortex (e.g., locus ceruleus, nucleus dorsalis raphe, etc.…”

The pattern of interhemispheric connections and its relationship to extrastriate visual areas in the macaque monkey

“…To the contrary, many callosal projections have been shown to be heterotopic (Zeki, 1971;Hedreen and Yin, 1981;Segraves and Rosenquist, 1982), and it has even been demonstrated that there are reciprocal interhemispheric connections between cortical and subcortical structures such as the claustrum (LeVay and Sherk, 1981).…”