neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

, 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 cuneus (; : cunei) is a smaller lobe in the occipital lobe of the brain. The cuneus is bounded anteriorly by the parieto-occipital sulcus and Inferior (anatomy), inferiorly by the calcarine sulcus. Function The cuneus (Brodmann area 17) r ...

(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 Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...

, visuospatial processing, reflections upon

self In philosophy, the self is an individual's own being, knowledge, and values, and the relationship between these attributes. The first-person perspective distinguishes selfhood from personal identity. Whereas "identity" is (literally) same ...

, and aspects of

consciousness Consciousness, at its simplest, is awareness of a state or object, either internal to oneself or in one's external environment. However, its nature has led to millennia of analyses, explanations, and debate among philosophers, scientists, an ...

. The location of the precuneus makes it difficult to study. Furthermore, it is rarely subject to isolated injury due to

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

s, 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 was first used in 1868 and the English ''precuneus'' in 1879.

Structure

The precuneus is located on the inside between the two

cerebral hemisphere The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres ...

s in the rear region between the somatosensory cortex and forward of the

(which contains the

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalam ...

). 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

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s (parallel fMRI research has also been done upon monkeys).

Subdivisions

;Sensorimotor Anterior Region 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 The premotor cortex is an area of the motor cortex lying within the frontal lobe of the brain just anterior to the primary motor cortex. It occupies part of Brodmann's area 6. It has been studied mainly in primates, including monkeys and human ...

, 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 The superior temporal gyrus (STG) is one of three (sometimes two) gyri in the temporal lobe of the human brain, which is located laterally to the head, situated somewhat above the external ear. The superior temporal gyrus is bounded by: * the l ...

. No connections with the inferior parietal lobule,

prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. It is the association cortex in the frontal lobe. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, ...

nor primary motor cortex. ;Cognitive/Associative Central Region 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 In cognitive science and neuropsychology, executive functions (collectively referred to as executive function and cognitive control) are a set of cognitive processes that support goal-directed behavior, by regulating thoughts and actions thro ...

working memory Working memory is a cognitive system with a limited capacity that can Memory, hold information temporarily. It is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term m ...

and

motor planning In psychology and neuroscience, motor planning is a set of processes related to the preparation of a movement that occurs during the reaction time (the time between the presentation of a stimulus to a person and that person's initiation of a motor ...

. ;Visual Posterior Region This occurs along the parieto-occipital fissure (yellow in figure). This connects with visual areas in the

and

primary visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus ...

Subcortical connections

Below the cerebral cortex, the precuneus is connected with the dorsalmost nuclei of the

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

, 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 The caudate nucleus is one of the structures that make up the corpus striatum, which is part of the basal ganglia in the human brain. Although the caudate nucleus has long been associated with motor processes because of its relation to Parkinso ...

, putamen, and the zona incerta. It also has links with the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

areas such as the

pretectal area In neuroanatomy, the pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical visual system. Through reciprocal bilateral projections from the retina, it is involved primarily in medi ...

, the

superior colliculus In neuroanatomy, the superior colliculus () is a structure lying on the tectum, roof of the mammalian midbrain. In non-mammalian vertebrates, the Homology (biology), homologous structure is known as the optic tectum or optic lobe. The adjective f ...

, the nucleus reticularis tegmenti pontis, and the basis pontis.

Function

The mental imagery concerning the

has been located in the forward part of the precuneus with posterior areas being involved with

. 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 etpinpoint what the precuneus does in itch, but it’s uniquely activated with itch and not pain.’”

Self

Functional imaging Functional imaging (or physiological imaging) is a medical imaging technique of detecting or measuring changes in metabolism, blood flow, regional chemical composition, and absorption. As opposed to structural imaging, functional imaging center ...

has linked the precuneus to the processes involved in

self-consciousness Self-consciousness is a heightened sense of awareness of oneself. It is not to be confused with consciousness in the sense of qualia. Historically, "self-consciousness" was synonymous with " self-awareness", referring to a state of awareness th ...

, 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.

Memory

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. The precuneus is also involved in source 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. 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 The hippocampus (: hippocampi; via Latin from Ancient Greek, Greek , 'seahorse'), also hippocampus proper, is a major component of the brain of humans and many other vertebrates. In the human brain the hippocampus, the dentate gyrus, and the ...

. 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.

Visuospatial

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. It is involved in motor imagery and shifting attention between motor targets. It is also involved in

motor coordination In physiology, motor coordination is the orchestrated movement of multiple body parts as required to accomplish intended actions, like walking. This coordination is achieved by adjusting kinematic and kinetic parameters associated with each bo ...

that requires shifting attention to different spatial locations. It is also together with the dorsal

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 orbitofrontal cortex (OFC) is a prefrontal cortex region in the frontal lobes of the brain which is involved in the cognitive process of decision-making. In non-human primates it consists of the association cortex areas Brodmann area 11, 1 ...

, the precuneus is activated when people make judgments that require understanding whether to act out of

empathy Empathy is generally described as the ability to take on another person's perspective, to understand, feel, and possibly share and respond to their experience. There are more (sometimes conflicting) definitions of empathy that include but are ...

and

forgiveness Forgiveness, in a psychology, psychological sense, is the intentional and voluntary process by which one who may have felt initially wronged, victimized, harmed, or hurt goes through a process of changing feelings and attitude regarding a given ...

Executive functions

Precuneus is thought to be related to response inhibition.

Consciousness

It has been suggested that together with the posterior cingulate, the precuneus is "pivotal for conscious information processing". The evidence for this link with

comes from the effects of its disruption in

epilepsy Epilepsy is a group of Non-communicable disease, non-communicable Neurological disorder, neurological disorders characterized by a tendency for recurrent, unprovoked Seizure, seizures. A seizure is a sudden burst of abnormal electrical activit ...

, brain lesions and vegetative state. Also, cerebral glucose metabolism is at its highest in these two areas during

wakefulness Wakefulness is a daily recurring brain state and state of consciousness in which an individual is conscious and engages in coherent cognition, cognitive and behavioral responses to the external world. Being awake is the opposite of being asleep, ...

but is most reduced in them during

anesthesia Anesthesia (American English) or anaesthesia (British English) is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prev ...

. In addition, it is one of the areas of the brain most deactivated during slow-wave sleep and rapid eye movement sleep. 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) than subliminal (and so do not enter consciousness).

Default network

It has been suggested to be the 'core node' or 'hub' of the

default mode network In neuroscience, the default mode network (DMN), also known as the default network, default state network, or anatomically the medial frontoparietal network (M-FPN), is a large-scale brain network primarily composed of the dorsal medial prefro ...

that is activated during "resting consciousness" in which people do not engage intentionally in sensory or motor activity. This involvement in the default network is suggested to underlie its role in

. However its involvement in the default network has been questioned. Though one of the authors raising these doubts noted "our findings in this regard should be treated as preliminary." A later study in 2012 showed that only ventral precuneus is involved in the default network.

Parietal prefrontal central hub

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 uchhubs 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.

Correlation of grey matter volume and subjective happiness score

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

Impact of mindfulness

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

Other animals

The precuneus seems to be a recently expanded part of the brain, as in less developed

primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

s 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".

Additional images

File:Precuneus animation.gif, Precuneus of left cerebral hemisphere (shown in red). File:Cerebral Gyri - Medial Surface1.png, Medial surface of left cerebral hemisphere. (Precuneus visible at top left.) File:Human brain inferior-medial view with marked Precuneus.JPG, Medial surface of left cerebral hemisphere. (Precuneus colored in red.) File:ParietCapts medial.png, Boundaries of precuneus are defined by the three sulci. (shown in red) The area colored blue represents

parietal lobe The parietal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integra ...

. File:Cerebral Hemisphere Demonstration - Sanjoy Sanyal - Neuroscience Lab Fall 2013 (Cropped from 30m22s to 31m22s) Precuneus.webm, Human brain dissection video (1 min). Demonstrating the location of precuneus. ("SPL" in the video, means Superior parietal lobule) File:Precuneus - DK ATLAS.png, Precuneus of right cerebral hemisphere. File:Precuneus coronal sections.gif, Precuneus highlighted in green on coronal T1 MRI images File:Precuneus sagittal sections.gif, Precuneus highlighted in green on sagittal T1 MRI images File:Precuneus transversal sections.gif, Precuneus highlighted in green on transversal T1 MRI images

References

External links

* - "Cerebral Hemisphere, Medial View" {{Authority control Articles containing video clips Gyri Medial surface of cerebral hemisphere Parietal lobe