Individual differences in the brain

Date:
August 10, 2020
Source:
Max-Planck-Gesellschaft
Summary:
If selection reinforces a behavior, brain activities soon change
as well.



FULL STORY ========================================================================== Personality varies widely. There are bold and reserved individuals,
who behave very differently when faced with the same environmental
stimulus. What is true for humans also applies to fish: their behavior
shows a range of individual differences. By selectively breeding
zebrafish, scientists from the Max Planck Institute of Neurobiology
were able to show that distinct personality traits rapidly emerge and
manifest not only in the behavior, but also through far- reaching changes
in the brain.


========================================================================== Young zebrafish are just five millimeters long and almost transparent.

Nevertheless, the tiny fish display a spectrum of behavior in response
to external stimuli. While some animals flee in panic at a loud sound,
other fish remain calm. If the sound is repeated, fish in one group learn
to ignore it quickly, while others never really get used to it. Between
these two extremes - - relaxed or skittish -- there is a whole range of behavioral expressions.

Carlos Pantoja and colleagues in Herwig Baier's team were now able to
show that selection for a specific behavioral trait can also change
the fishes' brain activity surprisingly quickly. The researchers mated
animals only within the extremely relaxed and the extremely skittish
groups. After just two generations, the brains of the fry selected for skittishness differed significantly from the brains of the calm offspring.

In the transparent fish larvae, the scientists were able to observe which
brain regions were activated by the loud sound. The offspring of the two behavioral extremes showed clear differences in neuronal activity in a
part of the hypothalamus and in the so-called dorsal raphe nucleus. A noticeable difference between these two brain regions is that the plastic
part of the hypothalamus contains neurons that secrete dopamine, while
the raphe nucleus mainly produces serotonin. Dopamine and serotonin
are two prominent neuromodulators that have also been associated with personality differences and even psychiatric conditions in humans.

"The ratio of cell activity in these two brain regions could regulate
the sensitivity of an individual fish's reaction to the sound and how
quickly it gets used to it," explains Carlos Pantoja. "However, this is certainly only one component, as there are also differences in a whole
range of other brain areas." Interestingly, the offspring of the two
fish groups not only showed the expected differences in their startle
response. While in the larval stage, the more relaxed fish fry was also significantly less spontaneously active. As adults, these fish then
adapted much slower to a new environment than adult jumpy fish. "At first glance, this sounds paradoxical. But it could be that the early tendency
to fearful overreactions tends to dampen the later stress response,"
says Pantoja. Similar long-term effects of early stress processing have
been reported in mammals.

In both groups of fish, the dopamine-releasing part of the hypothalamus
was activated during the startle reaction. However, while this region
was only switched on by the sound in the relaxed fish, it was permanently active in the skittish fish. After a mere two generations of behavioral selection, these animals already seemed to be constantly prepared
to escape.

"The pace at which personality traits can be shifted and fixed in
evolution is remarkable," reflects Herwig Baier. "The process might be similarly rapid in populations of Homo sapiens." The zebrafish could
perhaps reveal some of the involved brain structures and the genetic
basis of this plasticity.


========================================================================== Story Source: Materials provided by Max-Planck-Gesellschaft. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Carlos Pantoja, Johannes Larsch, Eva Laurell, Greg Marquart, Michael
Kunst, Herwig Baier. Rapid Effects of Selection on
Brain-wide Activity and Behavior. Current Biology, 2020; DOI:
10.1016/j.cub.2020.06.086 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200810113222.htm

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