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Evolutionary and hereditary axes shape our brains

Evolutionary and hereditary axes shape our brains

The human brain is organized on two axes. This principle seems to pass through the brain organization of all primates. Credit: Valk / MPI CBS

A country̵

7;s location on earth speaks volumes about its climate, neighboring countries, and the resources that can be found there. Therefore, the location determines what country you would expect to find at this time.

The same seems to apply to the brain. Each network is located in a specific place, which determines its function and neighbors, but also the type of function that appears there. The rules that describe the relationships between different brain regions have not been well understood so far. Scientists from the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany and the Forschungszentrum Juelich, together with an international team of collaborators, have deciphered two axes along which the human brain is organized. These axes have been found to be determined mainly by genetic factors.

One axis extends from the posterior (posterior) to the front of the cortex. This reflects a functional hierarchy from basic abilities such as vision and movement to abstract, extremely complex skills such as cognition, memory and social skills. A second axis leads from the dorsal (upper) to the ventral (lower) part of the cortex. While the ventral system is associated with functions that give meaning and motivation, the spinal system can refer to space, time, and movement.

“Interestingly, this vertical arrangement is consistent with the long-standing dual-origin hypothesis,” said Sophie Valk, head of the research group at MPI CBS and Forschungszentrum Juelich and the first author of the study, published in Scientific progress. According to this hypothesis, the cerebral cortex developed from two different origins, the amygdala and the olfactory cortex on the one hand and the hippocampus on the other. From this origin arise two different lines of cortical development, reflecting waves from less to more differentiated areas, starting from each origin. Such differences between the ventral and dorsal areas have been found in various mammals, such as primates, non-humans, cats, and rats. However, scientists around Valk have already provided evidence for it for the entire human cortex and have shown that this may be a second important organizational principle up to the posterior-frontal axis.

Evolutionary and hereditary axes shape our brains

A) The wasps in humans, on which the genetic correlation of the thickness of the bark is organized B) The wasps in the macaques, on which they deceive the thickness of the bark. The equal colors in A and B show that the main axis in humans corresponds to the second axis in macaques, and the second axis in humans corresponds to the first axis in macaques. Regions of the same color have a similar pattern of covariance, are genetically more similar than regions of different colors. Credit: Scientific progress

This biaxial organization, in turn, is largely determined by the genetic link between brain regions. This means that the relationship between the structure of two brain regions is determined by shared genetic effects. Moreover, similar axes have been found in the brains of macaque monkeys, indicating that these axes have been preserved by primate evolution. “At the same time, even if genes and evolution shape the organization of the brain structure, we must not forget that the environment also plays a crucial role in shaping our brains and minds,” says Valk. “Although in the present study we focused specifically on these genetic effects, other work by our team showed that behavioral learning can also change the structure of the brain.” Further research is planned to understand how these two factors that shape the brain structure interact.

Understanding the basic axes of brain organization is like having a compass and can help better orient the brain. “We can better understand the evolution and functions of specific regions and better assess the impact of brain disorders,” Valk added. For example, previous work by the authors shows that organizational axes differ between individuals with autism spectrum disorder and healthy controls.

Scientists have studied the organization of the brain structure using a multi-level approach. First, they used identical and dizygotic twins, as well as unrelated individuals, to model what part of the brain’s organization is genetically determined. They measure how the thickness of the cortex correlates in a group of individuals, which provides information about the structural and development of the connection between different brain regions. For example, if some relationships are stronger in monozygotic twins than in other siblings, it is probably due to genetic factors. Using genetic information about the connections between different brain regions, they calculate the main axes along which genetically similar brain structures are organized. They also compared the brain organization in humans to that in macaque monkeys. Finding similar wasps in these animals, they concluded that this organization was preserved in the evolution of primates.

The human brain: not just big, but fine

More information:
Sofie L. Valk et al, Forming brain structure: Genetic and phylogenetic axes of macroscale organization of cortex thickness, Scientific progress (2020). DOI: 10.1126 / sciadv.abb3417

Provided by the Max Planck Society

Quote: Evolutionary and hereditary axes form our brain (2020, September 28), extracted on September 30, 2020 from https://medicalxpress.com/news/2020-09-evolutionary-heritable-axes-brain.html

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