Comparative Anatomy of the Claustrum in Selected Species: A Morphometric Analysis

Abstract

The morphology of the claustrum was studied by stereological methods in representatives of five mammalian orders (Insectivora, Rodentia, Lagomorpha, Carnivora and Primates). In each species under study, a dorsal and a ventral part of the nucleus can be distinguished. Based on differences in shape and separation from surrounding structures, five morphological types of the claustrum occur. The claustrum of Insectivora and some rodents represents the least complicated morphological type. The nucleus is very poorly separated from the surrounding structures. The human claustrum is morphologically the most complicated, although the two above-mentioned principal divisions are apparent. The ventrally situated paraamygdalar part of the human claustrum may correspond to the endopiriform nucleus or ventral part of the claustrum of other mammals, because of its morphological characteristics and connections with the limbic system. In guinea pigs, traditionally classified as members of the Rodentia, a characteristic morphological type of the claustrum is present. This observation may support arguments questioning the current position of this species in mammalian classification. Based on stereological studies, the increase of the claustral volume that occurs with increase of the hemispheric volume is significantly smaller than the increase of the isocortical volume and larger than the increase of the allocortical volume. The increase of the volume of the dorsal and ventral parts of the claustrum does not differ significantly in the species under study. Neurons of the claustrum represent differentiated morphology. The numerical density of neurons in the dorsal part of the claustrum is significantly higher than in the ventral one. Differences in the morphology and cellular structure of the two parts of the claustrum may suggest differences in function of the two parts of the nucleus, most probably concerned with transfer of information among various cortical regions. Changes in the claustrum, a cortico-related structure, that occur with increased brain volume, may suggest that its development is less dynamic than that of the isocortex.

Psychedelics

“…Furthermore, as the cortex has expanded through evolution in different species, the size of the claustrum has actually decreased in relative size (Kowianski et al, 1999).…”

What is the function of the claustrum?

“…The claustrum is present in all mammalian species so far examined (Kowianski et al 1999), from insectivore to man, though its precise shape and some of its connections appear to vary from species to species. 2 We shall consider mainly the cat and primate claustrum (for comprehensive reviews, consult Sherk 1986;Tanné-Gariépy et al 2002;Edelstein & Denaro 2004).…”

“…It is thin and fairly small-in humans, its volume is a quarter of one percentage of that of the cerebral cortex (Kowianski et al 1999)-and so it is easily overlooked. Crick (1994) described the claustrum briefly, but since then we have left it to one side.…”

Susceptibility to Kindling and Neuronal Connections of the Anterior Claustrum

“…The claustrum is a thin column of gray matter in the rostral half of the forebrain between the basal ganglia and cortex (Kowianski et al, 1999). The functions of the claustrum are unclear, although data suggest that it may be involved in coordination of sensorimotor or motor control (Olson and Graybiel, 1980;Crescimanno et al, 1989;Salerno et al, 1989;Cortimiglia et al, 1991;Shima et al, 1996), voluntary swallowing (Zald and Pardo, 1999), nociception (Sloniewski et al, 1995;Persinger et al, 1997), and conditioned fear (Beck and Fibiger, 1995), and may become pathological in Alzheimer's disease or aging (Ogomori et al, 1989;Morys et al, 1994Morys et al, , 1996a and Parkinson's disease (Yoshimura et al, 1988).…”