what happens in Alzheimer’s

The precuneus, a region of the brain responsible for self-awareness, body perception, autobiographical memory and the construction of identity, adopts its definitive form very early, and its individual variability is already appreciated from birth, which is why it would be associated with genetic factors and prenatal development, according to a study led by the researcher of the National Museum of Natural Sciences (MNCN-CSIC) Emiliano Bruner.

“Situated between the two cerebral hemispheres, the precuneus is a key region for complex processes such as imagination, consciousness and the construction of the self. The upper part integrates somatic and visual information to place the body in a spatial framework, while the lower part connects this information with the episodic memory of personal experiences,” he explained. Emiliano Brunerfirst author of the study.

The work, published in Cerebral Cortexhas analyzed for the first time the development of this brain region from birth to adulthood. According to the research, the lower and upper regions of this central piece of the brain network grow independently, have different functions and wiring, so they should not be studied together, as is usually done today.

This study emphasizes that the organization of the precuneus is not homogeneous, but responds, on the one hand, to a longitudinal axiswhich combines somatic and visual information; and on the other hand, to a vertical axiswhich integrates that information with memory and consciousness. This anatomical complexity explains why it is considered a central node in the brain network and why its variability between individuals can have implications for processes as sophisticated as imagination or the construction of the self. “It is a central node of the entire brain network, both at the level of connections and cognitive abilities, which is why it is so relevant to know its morphology and functioning,” Bruner highlighted.

For this work, the researchers subjected MRI tests and morphometric analyzes to 220 people, from newborns to young adults, in order to follow the evolution of the precuneus. Thus, they observed that the definition of this area occurred before others, which mature during childhood and adolescence.

The most important changes in the size of the precuneus They are only detected between birth and two or three years of age and afterwards this brain structure hardly changes. In turn, the enormous individual variability in the shape of the precuneus, which is already seen from birth, does not seem to be due to learning or experience, but, in large part, to genetic factors and prenatal development.

In other words, each person is born with a precuneus that already resembles adult proportions, which could influence aspects as essential as body awareness or autobiographical memoryalthough it is not yet known how it translates into cognitive differences.

“The striking thing is that these differences do not occur as we grow, but rather are given by genetic factors and intrauterine processes. We could say that we come into the world with a practically complete precuneus, that is, the anatomical cards are laid out before we are born, although that does not exclude that its functions can later be developed or trained,” Bruner insisted.

Differences in Alzheimer’s disease

Another study, whose first author is also Emiliano Bruner, recently published in Journal of Anatomyhas focused on verifying the differences in the precuneus during normal aging and when Alzheimer’s disease occurs.

They were compared 39 brains of people with this neurodegenerative disease, confirmed post-mortem, from the BT-CIEN Tissue Bank, with a control group made up of 42 brains of older people without cognitive impairment Vallecas Projectwhich had been tracked for a decade.

The work shows that in normal aging the upper area of ​​the precuneus tends to show more open grooves due to the loss of tissue, while the lower area progressively reduces its size. However, in people with Alzheimer’s this reduction is more pronounced and this region is progressively invaded by adjacent brain tissues.

Although it was known that the precuneus is one of the most vulnerable areas in the early stages of Alzheimer’s, this work describes for the first time in detail as varies its shape and anatomical organization compared to normal aging, which helps to understand why the evolutionary expansion of this brain region in our species is especially sensitive to neurodegeneration.

Emiliano Bruner has dedicated more than 25 years to study the evolution of the human parietal lobes and this article is the ninth dedicated to the anatomical analysis of the precuneus, a fundamental cortical element to understand how the unique cognitive abilities in the human species emerged.

Paleoneurological evidence, through reconstruction of the brain of extinct species from the internal cavity of the skull, suggests that this region of the brain has undergone an expansion in the human species, Homo sapiens, although the differences between humans and other primates remain poorly understood.