Прекунеус: анатомия, функции и связи в мозге

Region of the parietal lobe of the brain

In neuroanatomy, 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 parieto occipital 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". The Latin form of praecuneus was first used in 1868 and the English precuneus in 1879.

[[File:Precuneus connectivity new. gif|thumb|300px|Subdivisions of precuneus and posterior cingulate in the human based upon resting state functional connectivity.

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. Another area has been linked to visuospatial 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 “‘We can’t [yet] pinpoint what the precuneus does in itch, but it’s uniquely activated with itch and not pain.’”

Functional imaging has linked the precuneus to the processes involved in self consciousness, such as reflective self awareness, that involve rating one's own personality traits compared to those judged of other people. Electrical stimulation of the anterior portion can induce an out of body experience.

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. It is involved with the left prefrontal cortex in the recall of episodic memories including past episodes related to the self. 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 the hippocampus. Alternatively it has a different involvement when judging the familiarity as it decides whether the processing of perceptual features would be more useful. In this way the precuneus gets involved in diverse processes such as attention, episodic memory retrieval, working memory and conscious perception. It is involved in motor imagery and shifting attention between motor targets. It is also together with the dorsal premotor cortex involved in visuospatial mental operations (such as in a modified form of the game of Amidakuji). 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. 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. Together with the superior frontal gyrus and orbitofrontal cortex, the precuneus is activated when people make judgments that requires understanding whether to act out of empathy and forgiveness.

Precuneus is thought to be related to response inhibition.

It has been suggested that together with the posterior cingulate, the precuneus is "pivotal for conscious information processing". The evidence for this link with consciousness comes from the effects of its disruption in epilepsy, brain lesions and vegetative state.

It has been suggested to be the 'core node' or 'hub' of the default mode network that is activated during "resting consciousness" in which people do not engage intentionally in sensory or motor activity. Though one of the authors raising these doubts noted "our findings in this regard should be treated as preliminary."

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.

A positive relationship has been found between the volume of grey matter in the right precuneus and the subject's subjective happiness score.

A 6 week mindfulness based intervention was found to correlate with a significant grey matter increase within the precuneus.

The precuneus seems to be a recently expanded part of the brain, as in less developed primates such as New world monkeys "the superior parietal and precuneate regions are poorly developed". 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".