Claustrum

The claustrum (Latin, meaning "to close" or "to shut") is a thin sheet of neurons and supporting glial cells, that connects to the cerebral cortex and subcortical regions including the amygdala, hippocampus and thalamus of the brain. It is located between the insula laterally and the putamen medially, separated by the extreme and external capsules respectively. Blood to the claustrum is supplied by the middle cerebral artery. It is considered to be the most densely connected structure in the brain, and thus hypothesized to allow for the integration of various cortical inputs such as vision, sound and touch, into one experience. Other hypotheses suggest that the claustrum plays a role in salience processing, to direct attention towards the most behaviorally relevant stimuli amongst the background noise. The claustrum is difficult to study given the limited number of individuals with claustral lesions and the poor resolution of neuroimaging. The claustrum is made up of various cell types differing in size, shape and neurochemical composition. Five cell types exist, and a majority of these cells resemble pyramidal neurons found in the cortex. Within the claustrum, there is no organization of cell types compared to the cortex, and the cell bodies can be a pyramidal, fusiform or circular. The principal cell type found in the claustrum is the Golgi type I neuron, which are large cells covered in spiny dendrites. Through interhemispheric connections, the claustrum is believed to play a role in synchronizing activity in widely separated, but functionally related, parts of the brain (e.g. frontal eye fields and visual cortex). As such, the claustrum is thought to play a role in combining different information modalities potentially to support consciousness itself. Another proposed functions of the claustrum is to differentiate between relevant and irrelevant information so that the latter can be ignored. Cortical components of consciousness include the fronto-parietal cortex, cingulate and precuneus.