The functional neuroimaging of the precuneus.

Over the last few years functional neuroimaging studies have started unravelling unexpected functional attributes for the precuneus, a previously neglected area located in the posteromedial parietal cortex. Multiple sources of evidence from fMRI and PET investigations suggest a central role for the precuneus in a wide spectrum of highly integrated tasks, including visuo-spatial imagery, episodic memory retrieval, and selfprocessing operations, namely first-person perspective taking and an experience of agency. Furthermore, the precuneus and surrounding structures within the posteromedial parietal region are thought to represent a crucial node in the ‘default mode’ system, a network of brain structures displaying high resting metabolic rate and transient deactivations during engagement in non self-referential tasks. Therefore, it has recently been proposed that the precuneus plays a pivotal role in the neural correlates of consciousness, engaged in self-related mental representations during rest. This hypothesis is consistent with the selective hypometabolism in the posteromedial cortex reported in a wide range of pathophysiological states characterised by altered consciousness, such as sleep, vegetative state, and pharmacological anaesthesia. Functional neuroimaging studies on neuropsychiatric populations showing disruption of the ‘default mode’ activity have recently added novel insights into the understanding of the behavioural correlates of the precuneus.