| Precuneus | |
|---|---|
 Medial surface of left cerebral hemisphere. (Precuneus visible at top left.) (Anterior to the right.) | |
 Sagittal MRI slice with the precuneus shown in red. (Anterior to the left.) | |
| Details | |
| Identifiers | |
| Latin | praecuneus |
| NeuroNames | 110 |
| NeuroLex ID | birnlex_1446 |
| TA98 | A14.1.09.223 |
| TA2 | 5479 |
| FMA | 61900 |
| Anatomical terms of neuroanatomy | |
Inneuroanatomy, theprecuneus is the portion of thesuperior parietal lobule on themedial surface of each brainhemisphere. It is located in front of thecuneus (the upper portion of theoccipital lobe). The precuneus is bounded in front by themarginal branch of thecingulate sulcus, at the rear by theparieto-occipital sulcus, and underneath by thesubparietal sulcus. It is involved withepisodic memory,visuospatial processing, reflections uponself, and aspects ofconsciousness.
The location of the precuneus makes it difficult to study. Furthermore, it is rarely subject to isolated injury due tostrokes, or trauma such as gunshot wounds. This has resulted in it being "one of the less accurately mapped areas of the whole cortical surface".[1] While originally described as homogeneous byKorbinian Brodmann, it is now appreciated to contain three subdivisions.[2]
It is also known afterAchille-Louis Foville as thequadrate lobule of Foville.[1][3][4] The Latin form ofpraecuneus was first used in 1868 and the Englishprecuneus in 1879.[5]
The precuneus is located on the inside between the twocerebral hemispheres in the rear region between thesomatosensory cortex and forward of thecuneus (which contains thevisual cortex). It is above theposterior cingulate. FollowingKorbinian Brodmann it has traditionally been considered a homogeneous structure and with limited distinction between it and the neighboringposterior cingulate area. Brodmann mapped it as the medial continuation of lateral parietalarea 7.
Axon tracing research onmacaque monkeys has established that it consists of three subdivisions which now have been confirmed byfMRI upon resting-statefunctional connectivity to also exist inhumans (parallel fMRI research has also been done upon monkeys).[2]
This occurs around the margin of thecingulate sulcus ( blue in figure) and is connected with sensorimotor areas of the cerebral cortex such as theparacentral lobule,supplementary motor area,premotor cortex,somatosensory area (Brodmann area 2),parietal operculum andinsula. fMRI Research upon humans finds a connection with the caudalmost part ofparahippocampus andsuperior temporal gyrus. No connections with theinferior parietal lobule,prefrontal cortex norprimary motor cortex.
This occurs around the precuneal sulcus ( green in figure) and is connected with theinferior parietal lobule particularly theangular gyrus and prefrontal areas10,46 and8. No connections exist with premotor, motor, or somatosensory areas. The areas with which it links are involved inexecutive functions,working memory andmotor planning.
This occurs along the parieto-occipital fissure ( yellow in figure). This connects with visual areas in thecuneus andprimary visual cortex.
Below the cerebral cortex, the precuneus is connected with the dorsalmost nuclei of thethalamus, including theventral lateral nucleus, the central and anterior nuclei of theintralaminar nuclear group, and the lateralpulvinar. Other connections include theclaustrum, the dorsolateralcaudate nucleus,putamen, and thezona incerta.[1][3] It also has links with thebrainstem areas such as thepretectal area, thesuperior colliculus, thenucleus reticularis tegmenti pontis, and thebasis pontis.[1][3]
Themental imagery concerning theself has been located in the forward part of the precuneus with posterior areas being involved withepisodic memory.[6] Another area has been linked tovisuospatial imagery. (It is not though clear how these—and the functions noted below—link with the above three subdivisions.)
The precuneus plays a role in itch sensations (there are many different types of itch) and their brain processing[7] "'We can't [yet] pinpoint what the precuneus does in itch, but it's uniquely activated with itch and not pain.'"[8]
Functional imaging has linked the precuneus to the processes involved inself-consciousness, such as reflective self-awareness, that involve rating one's own personality traits compared to those judged of other people.[9][10]
Electrical stimulation of the anterior portion can induce anout of body experience.[11]
The precuneus is involved in memory tasks, such as when people look at images and try to respond based on what they have remembered in regard to verbal questions about their spatial details.[12] It is involved with the left prefrontal cortex in the recall ofepisodic memories[13][14] including past episodes related to the self.[10] The precuneus is also involved insource memory (in which the "source" circumstances of a memory are recalled) with the left inferior prefrontal cortex: here its role is postulated to be providing rich episodic contextual associations used by the prefrontal cortex to select the correct past memory.[15] In the recollection of memories, it has been postulated that the precuneus discerns whether contextual information exists that can be useful for involving the aid of thehippocampus.[citation needed] Alternatively it has a different involvement when judging the familiarity as it decides whether the processing of perceptual features would be more useful.[16] In this way the precuneus gets involved in diverse processes such as attention, episodic memory retrieval, working memory and conscious perception.[16]
The precuneus has been suggested to be involved in directing attention in space both when an individual makes movements and when imaging or preparing them.[1][17] It is involved in motor imagery and shifting attention between motor targets.[1] It is also involved inmotor coordination that requires shifting attention to different spatial locations.[18] It is also together with the dorsalpremotor cortex involved invisuospatial mental operations (such as in a modified form of the game ofAmidakuji). It is suggested that while the premotor area engages in the mental operation, the precuneus aids monitoring the success of that operation in terms of internally represented visual images.[19]
The precuneus' role in mental imagery has been suggested to extend to that of modeling other people's views. It is activated when a person takes a third-person versus first-person visual point of view.[20] Together with thesuperior frontal gyrus andorbitofrontal cortex, the precuneus is activated when people make judgments that require understanding whether to act out ofempathy andforgiveness.[21]
Precuneus is thought to be related to response inhibition.[22]
It has been suggested that together with the posterior cingulate, the precuneus is "pivotal for conscious information processing".[23] The evidence for this link withconsciousness comes from the effects of its disruption inepilepsy,brain lesions andvegetative state.[3][23] Also, cerebral glucose metabolism is at its highest in these two areas duringwakefulness but is most reduced in them duringanesthesia.[3][23] In addition, it is one of the areas of the brain most deactivated duringslow-wave sleep andrapid eye movement sleep.[3]
Together with the prefrontal cortex, the precuneus, is more activated upon the learning of words briefly flashed when they are supraliminal (and so enter consciousness) thansubliminal (and so do not enter consciousness).[24]
It has been suggested to be the 'core node' or 'hub' of thedefault mode network that is activated during "resting consciousness" in which people do not engage intentionally in sensory or motor activity.[3] This involvement in the default network is suggested to underlie its role inself-consciousness. However its involvement in the default network has been questioned.[2][25] Though one of the authors raising these doubts noted "our findings in this regard should be treated as preliminary."[2] A later study in 2012 showed that only ventral precuneus is involved in the default network.[26]
Olaf Sporns and Ed Bullmore have proposed that its functions link to its role as a central and well connected "small-world network" hub between parietal and prefrontal regions.
These clusters or modules are interlinked by specialized hub regions, ensuring that overall path lengths across the network are short. Most studies identified [such] 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.[27]
A positive relationship has been found between the volume ofgrey matter in the right precuneus and the subject's subjective happiness score.[28]
A 6-weekmindfulness based intervention was found to correlate with a significantgrey matter increase within the precuneus.[29]
The precuneus seems to be a recently expanded part of the brain, as in less developedprimates such asNew world monkeys "the superior parietal and precuneate regions are poorly developed".[1] It has been noted that "the precuneus is more highly developed (i.e. comprises a larger portion of the brain volume) in human beings than in non-human primates or other animals, has the most complex columnar cortical organization and is among the last regions to myelinate".[1]
