This part of the cerebral cortex is located in the parietal lobe and has several functions.
The human brain is a complex and fascinating organ. Each cerebral hemisphere is made up of several lobes.
And in the superior parietal lobe, hidden between layers of nerve fibers, we can find the pre-wedge, a unique region for its characteristics and for the functions that have been attributed to it as the main brain coordination center, as well as for participating in self-awareness processes. .
In this article we explain what the pre-wedge is, what its structure is and where it is located, what its main functions are and what role it plays in the development of Alzheimer’s disease.
Precuña: definition, structure and location
The pre-wedge or precuneus is a region located in the superior parietal lobe, hidden in the longitudinal fissure of the brain, between both hemispheres. It is bordered in front by the marginal branch of the cingulate sulcus, in the posterior part by the parieto-occipital sulcus and, below, by the subparietal sulcus.
At times, the pre-wedge has also been described as the medial area of the superior parietal cortex. In cytoarchitectural terms, it corresponds to Brodmann’s area 7, a subdivision of the parietal region of the cortex.
In addition, it has a complex cortical organization in the form of columns and is one of the brain regions that takes the longest to complete its myelination (a process by which axons are coated with myelin to, among other things, improve the speed of impulse transmission nervous). Its morphology shows individual variations, both in its shape and in longitudinal size.
Also, the pre-wedge has numerous neural connections ; at the cortical level, it connects with sensorimotor areas, with areas related to executive functions, memory and motor planning, and with the primary visual cortex; and at the subcortical level, it has important connections with the thalamic nuclei and the brain stem.
The pre-wedge is a structure that has developed more in humans than in animals, since at an evolutionary level there has been a considerable increase in the size (in shape and surface) of the parietal and frontal lobes of the human cerebral cortex compared to the rest of the animal kingdom, with what this implies regarding the development of higher cognitive functions. It is, therefore, a structure that has aroused great interest in the neuroscientific community, despite being anatomically so “elusive” (due to its location).
The pre-wedge is one of the main areas of regulation and integration of our brain, and acts as a kind of conductor through which many of the signals necessary for this organ to function as an integrated whole pass.
Below are the different functions attributed to the pre-wedge:
Autobiographical information (episodic memory)
The pre-wedge works in connection with the left prefrontal cortex, involved in processes that have to do with episodic memory and autobiographical memories. In this sense, it participates in aspects such as attention, the recovery of episodic memory, working memory or the processes of conscious perception.
1. Visuospatial processing
Another of the key functions in which the pre-wedge has been suggested to be involved is visuospatial processing; This area would participate in the management of spatial attention, when there are movements and, also, when images are generated.
It is also believed to be responsible for motor coordination in divided attention processes; that is, when it is required to shift attention to different places or spatial locations (eg when writing a text or drawing a painting). In addition, the pre-wedge would be activated, together with the premotor cortex, in mental operations that require visuospatial processing.
2. Self awareness
Various investigations have linked the pre-wedge with processes in which the conscience of oneself intervenes; In this sense, this brain region would have a relevant role in the integration of the perception of ourselves, in a network of spatial, temporal and social relationships. The pre-wedge would be in charge of generating that feeling of continuity between brain, body and environment.
In studies with functional images, it has been observed that this brain structure analyzes and interprets the “intention” of others with respect to ourselves ; that is, it would act as a mechanism for analyzing the judgments of others that require an adequate interpretation in order to act accordingly (eg with empathy).
3. Conscious perception
In addition to having a relevant role in self-awareness processes, it has been suggested that the pre-wedge could be, together with the posterior cingulate cortex, relevant for the processing and conscious perception of information.
It has been observed that cerebral glucose metabolism increases significantly during wakefulness, contrary to what occurs when under the influence of anesthesia. Also, during slow wave sleep and rapid eye movement or REM sleep, the pre-wedge would be virtually off.
On the other hand, it is believed that the cognitive functions related to this brain region could contribute to integrating internal information (which comes from the brain and our body) with environmental or external information; thus, the pre-wedge would play an essential role in the processes that generate consciousness and the mind in general.
4. Integrating core
More and more studies support the role of the pre-wedge as an integrating center of neural networks of the brain, due to its high centrality in the cortical network of this organ and its numerous and powerful connections with prefrontal areas in charge of executive functions such as planning. , supervision and decision making.
Pre-wedge in Alzheimer’s disease
The Alzheimer ‘s disease in its early stage, begins with metabolic problems in the area of the medial parietal lobes. It seems that the enlargement of these brain regions is what confers certain vulnerability to the subsequent neurodegeneration suffered by these patients.
Several studies have suggested that there may be a relationship between pregnancy and the development of this serious disease. As we have commented previously, the pre-wedge has evolved differently in humans than in animals: the main difference with respect to other primates, for example, is that this structure presents particularly high metabolic levels.
Apparently, the pre-wedge has higher levels of metabolic output than would correspond due to its size, which also occurs with its thermal values. The funny thing is that Alzheimer’s begins with metabolic problems precisely in the deep medial parietal area, where the pre-wedge is located. And a characteristic of Alzheimer’s is the phosphorylation of tau proteins, which occurs in mammals that hibernate in response to changes in temperature.
What neuroscientists suggest is that a pathology as frequent and characteristic of humans as Alzheimer’s would be associated with areas of the brain that have a specific morphology also in humans. And what they are questioning is whether the increase in the complexity of these brain areas could have also led to an increase in biological complexity that, secondarily, could cause an increase in metabolic load, oxidative stress and the cellular problems that predispose a person to suffer from Alzheimer’s disease.
However, the possible link between the pre-wedge and other similar structures with the development of this and other neurodegenerative diseases is currently being investigated, with the aim of finding new drugs and therapeutic targets that cure or, at least, slow their progress.
- Cavanna, AE, & Trimble, MR (2006). The precuneus: a review of its functional anatomy and behavioral correlates. Brain, 129 (3), pp. 564-583.
- Miners, JS, Palmer, JC, & Love, S. (2016). Pathophysiology of Hypoperfusion of the Precuneus in Early Alzheimer’s Disease. Brain Pathology, 26 (4), pp. 533-541.