What is the function of the claustrum?

Abstract

The claustrum is a thin, irregular, sheet-like neuronal structure hidden beneath the inner surface of the neocortex in the general region of the insula. Its function is enigmatic. Its anatomy is quite remarkable in that it receives input from almost all regions of cortex and projects back to almost all regions of cortex. We here briefly summarize what is known about the claustrum, speculate on its possible relationship to the processes that give rise to integrated conscious percepts, propose mechanisms that enable information to travel widely within the claustrum and discuss experiments to address these questions.

Figure 1

A drawing of the claustrum of a young squirrel monkey. The inset shows a single coronal section, illustrating the sheet-like structure of the claustrum. Modified from Brand (1981).

Figure 2

The approximate location of the human claustrum beneath the insular cortex. The vertical lines correspond to the two coronal sections shown at 60 and 70 mm posterior to the frontal pole. The external capsule consists of fibres making up the white matter lying between the putamen and the claustrum and the extreme capsule fibres that constitute the white matter between the claustrum and neocortex. The horizontal stripes correspond to the putamen and caudate nucleus and the vertical lines to the amygdala. Modified from Rae (1954).

Figure 3

Horseradish peroxidase (HRP) was injected into four distinct neocortical regions in the monkey and the distribution of labelled cells and extracellular granules (shown in coronal sections) in the claustrum was recovered. Note the overlap between claustral zones that communicate with somatosensory cortex (S1) and area four in the precentral gyrus, between claustral regions linked to striate and extrastriate visual cortex (areas 17 and 18) and areas eight and nine of the prefrontal lobe, and between claustral regions that are connected with area four and those connected to areas eight and nine. Modified from Pearson et al. (1982).

Figure 4

Neuronal cell types in the human claustrum as seen in Golgi preparations. (a) The dominant cell type (type I). They both receive input from cortex and send their axons back there. Their dendrites are covered with spines. (b), (c) At least two types of neurons whose dendrites are devoid of spines have been identified. Their axons do not leave the claustrum. They are most likely inhibitory interneurons. Modified from Braak & Braak (1982).