Precuneus

The precuneus is the portion of the superior parietal lobule on the medial surface of each brain hemisphere. It is located in front of the cuneus (the upper portion of the occipital lobe). The precuneus is bounded in front by the marginal branch of the cingulate sulcus, at the rear by the parietooccipital sulcus, and underneath by the subparietal sulcus. It is involved with episodic memory, visuospatial processing, reflections upon self, and aspects of consciousness.These clusters or modules are interlinked by specialized hub regions, ensuring that overall path lengths across the network are short. Most studies identified hubs among parietal and prefrontal regions, providing a potential explanation for their well-documented activation by many cognitive functions. Particularly notable is the prominent structural role of the precuneus, a region that is homologous to the highly connected posteromedial cortex in the macaque. The precuneus is involved in self-referential processing, imagery and memory, and its deactivation is associated with anaesthetic-induced loss of consciousness. An intriguing hypothesis suggests that these functional aspects can be explained on the basis of its high centrality in the cortical network.Precuneus of left cerebral hemisphere (shown in red).Medial surface of left cerebral hemisphere. (Precuneus visible at top left.)Medial surface of left cerebral hemisphere. (Precuneus colored in red.)Human brain dissection video (1 min). Demonstrating the location of precuneus. ('SPL' in the video, means Superior parietal lobule) The precuneus is the portion of the superior parietal lobule on the medial surface of each brain hemisphere. It is located in front of the cuneus (the upper portion of the occipital lobe). The precuneus is bounded in front by the marginal branch of the cingulate sulcus, at the rear by the parietooccipital sulcus, and underneath by the subparietal sulcus. It is involved with episodic memory, visuospatial processing, reflections upon self, and aspects of consciousness. The location of the precuneus makes it difficult to study. Furthermore, it is rarely subject to isolated injury due to strokes, or trauma such as gunshot wounds. This has resulted in it being 'one of the less accurately mapped areas of the whole cortical surface'. While originally described as homogeneous by Korbinian Brodmann, it is now appreciated to contain three subdivisions. It is also known after Achille-Louis Foville as the quadrate lobule of Foville. The Latin form of praecuneus was first used in 1868 and the English precuneus in 1879. The precuneus is located on the inside between the two cerebral hemispheres in the rear region between the somatosensory cortex and forward of the cuneus (which contains the visual cortex). It is above the posterior cingulate. Following Korbinian Brodmann it has traditionally been considered a homogeneous structure and with limited distinction between it and the neighboring posterior cingulate area. Brodmann mapped it as the medial continuation of lateral parietal area 7. Axon tracing research on macaque monkeys has established that it consists of three subdivisions which now have been confirmed by fMRI upon resting-state functional connectivity to also exist in humans (parallel fMRI research has also been done upon monkeys). This occurs around the margin of the cingulate sulcus (  blue in figure) and is connected with sensorimotor areas of the cerebral cortex such as the paracentral lobule, supplementary motor area, premotor cortex, somatosensory area (Brodmann area 2), parietal operculum and insula. fMRI Research upon humans finds a connection with the caudalmost part of parahippocampus and superior temporal gyrus. No connections with the inferior parietal lobule, prefrontal cortex nor primary motor cortex. This occurs around the precuneal sulcus (  green in figure) and is connected with the inferior parietal lobule particularly the angular gyrus and prefrontal areas 10, 46 and 8. No connections exist with premotor, motor, or somatosensory areas. The areas with which it links are involved in executive functions, working memory and motor planning. This occurs along the parieto-occipital fissure (  yellow in figure). This connects with visual areas in the cuneus and primary visual cortex. Below the cerebral cortex, the precuneus is connected with the dorsalmost nuclei of the thalamus, including the ventral lateral nucleus, the central and anterior nuclei of the intralaminar nuclear group, and the lateral pulvinar. Other connections include the claustrum, the dorsolateral caudate nucleus, putamen, and the zona incerta. It also has links with the brainstem areas such as the pretectal area, the superior colliculus, the nucleus reticularis tegmenti pontis, and the basis pontis.