Does the claustrum have a function? Lessons from human lesion and animal studies point to divergent multifunctionality

The claustrum is the most densely interconnected region in the human brain. Despite the accumulating data from clinical and experimental studies, the functional role(s) of the claustrum remain unknown. Here, we systematically review claustrum lesion studies and discuss their functional implications. Claustral lesions are associated with an array of signs and symptoms, including changes in cognitive, perceptual and motor abilities; electrical activity; mental state; and sleep. The wide range of symptoms observed following claustral lesions suggests that the claustrum may either have a number of distinct functions, or a global function that impacts many neural processes. We further discuss the implications of these lesions in the context of recent evidence linking the claustrum to sensory perception, sleep, and salience as well as highlighting an underexplored link between the claustrum and pain. We hypothesize that the claustrum is connected to multiple brain networks, both ancient and advanced, which underly fundamental functions as well as higher cognitive processes. Extensive evidence derived from human lesion studies and animal experiments provides unequivocal evidence for a key function of the claustrum as a multifunctional node in numerous networks.