Evolutionary and heritable axes shape our brain

Date:
September 28, 2020
Source:
Max Planck Institute for Human Cognitive and Brain Sciences
Summary:
Every region has its place in the brain. However, it has been
unclear why brain regions are located where they are. Now,
scientists have defined two main axes along which brain regions
are genetically organized, stretching from posterior to anterior
and inferior to superior in the brain. These axes are mainly shaped
by genes and evolution.



FULL STORY ==========================================================================
The location of a country on the earth says a lot about its climate, its neighboring countries, and the resources that might be found there. The location therefore determines what kind of country you would expect to
find at that point.


==========================================================================
The same seems to apply to the brain. Every network is located at a
certain place, which determines its function and neighbors but also the
kind of function that occurs there. However, the rules that describe
the relationships different brain regions have to each-other were not
well understood until now.

Scientists at 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. It was found that these axes
are mainly determined by genetic factors.

One axis stretches from the posterior (back) to the frontal part of
the cortex.

This reflects a functional hierarchy from basic capabilities such as
vision and movement to abstract, highly 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. Whereas the ventral system
has been associated with functions assigning meaning and motivation,
the dorsal system may relate to space, time, and movement.

"Interestingly, this vertical arrangement aligns with the long-held
hypothesis of dual origin," says Sofie Valk, research group leader
at the MPI CBS and Forschungszentrum Juelich and first author of the
study, published in Science Advances. According to this hypothesis,
the cerebral cortex developed from two different origins, the amygdala
and olfactory cortex on the one hand and the hippocampus on the other
hand. From these origins two different lines of cortical development
arose, reflecting waves from less to more differentiated areas starting
at each origin. Such distinctions between ventral and dorsal areas have
been found in various mammals, such as non-human primates, cats, and
rats. The scientists around Valk, however, have now provided evidence for
it for the entire human cortex, and shown this may be a second important organizational principle next to the posterior-frontal axis.

This two-axis-organization, in turn, is largely determined by the
genetic relation between brain regions. This means that the association
between the structure of two brain regions is driven by shared genetic
effects. Moreover, similar axes have been found in the brains of
macaque monkeys, indicating these axes are conserved through primate
evolution. "At the same time, even if genes and evolution shape the organization of brain structure, we must not forget the environment also
plays a crucial role in shaping our brains and minds," Valk says. "Though
we focused specifically on these genetic effects in the current study,
other work of our team has shown that behavioral training can also alter
brain structure." Further studies are planned to understand how these
two factors that shape brain structure interact.

To understand the major axes of brain organization is like having a
compass, and can help to better navigate in the brain. "We may better understand the evolution and function of specific regions and better
evaluate the impact of brain disorders," Valk adds. For example, previous
work of the authors has shown that organizational axes differ between individuals with autism spectrum disorder and healthy controls.

The scientists have investigated the organization of brain structure
using a multi-level approach. First, they used monozygotic and dizygotic
twins, as well as unrelated persons, to model how much of the brain's organization is genetically determined. They measured how the thickness
of the cortex correlated across a group of individuals, which provided information on the structural and developmental relationship between
different brain regions. If, for example, certain relationships were
stronger in monozygotic twins than in other siblings, this would
presumably be due to genetic factors. Using the genetic information
of the relationships between different brain regions, they computed
the major axes along which genetically similar brain structures are
organized. They also compared the brain organization in humans with
that in macaque monkeys. Finding similar axes in these animals, they
concluded that this organization is conserved across primate evolution.


========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Human_Cognitive_and_Brain Sciences. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sofie L. Valk, Ting Xu, Daniel S. Margulies, Shahrzad Kharabian
Masouleh,
Casey Paquola, Alexandros Goulas, Peter Kochunov, Jonathan
Smallwood, B.

T. Thomas Yeo, Boris C. Bernhardt, Simon B. Eickhoff. Shaping
brain structure: Genetic and phylogenetic axes of macroscale
organization of cortical thickness. Science Advances, 2020; 6
(39): eabb3417 DOI: 10.1126/sciadv.abb3417 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200928133147.htm

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