The tendency towards an increased willingness to take risks is evident both in the genes and in the brain. Scientists have found this out using brain scans and behavioral data from over 25,000 people. Risk-takers show less gray matter in brain areas such as the amygdala, the ventral striatum and the hypothalamus. In addition, genetic analyzes show that certain gene variants are also associated with reduced gray matter and risky behavior. However, only a small part of the behavior can be explained using genes.
Why do some people often exceed the speed limit, have sex with changing partners or indulge in excessive alcohol or tobacco consumption? Behaviors like this are considered appealing by many, but they are risky. Because they can have harmful health, social and financial consequences for the individual and the people around him. “People have varying degrees of inclination to engage in behavior that is dangerous to their health or that creates uncertainties about the future,” says Gideon Nave of the University of Pennsylvania.
Risk aversion through more gray cells?
Together with a team led by Gökhan Aydogan from the University of Zurich, he got to the bottom of the origin of this risk appetite. To do this, the researchers used an extensive data set from the UK Biobank, a long-term study in the UK that contains health and behavioral data from around 500,000 volunteers. For the first part of the study, Aydogan and colleagues analyzed brain scans of over 12,000 people. They compared these with information that these people had given about their personal risk behavior, i.e. about alcohol and cigarette consumption, sexual promiscuity and driving too fast.
The result: People who behave particularly risky had, on average, less gray matter in some brain areas. These are the parts of the central nervous system that are made up of the cell bodies of neurons. Gray matter is responsible for the basic functions of the brain, including muscle control, sensory perception, and decision-making. The local differences in the volume of this brain matter persisted when the researchers factored out other influencing factors such as age, gender and the total size of the brain. With an additional, independent data set from 13,000 other people, Aydogan and colleagues confirmed the finding.
Differences in many brain regions
In addition, the research team examined which specific brain regions had the strongest relationship between risk-taking and reduced gray matter. “We found out that there isn’t just one brain region that is the ‘risk area’,” says Nave. Instead, the researchers found associations with different regions of the brain, including the amygdala, which controls the emotional response to danger, for example, and the ventral striatum, which is active in processing rewards. Deviations were also found in the hypothalamus, which controls vegetative body functions by releasing hormones such as oxytocin and dopamine, in the hippocampus, which is involved in storing memories, and in the dorsolateral prefrontal cortex, which plays an important role in self-control and cognitive weighing.
To their surprise, the scientists even found anatomical deviations in the cerebellum, which was previously mainly associated with motor functions. The fact that this brain region could also be involved in cognition and decision-making was suspected, but scientifically underestimated. “It seems that the cerebellum still plays an important role in decision-making processes such as risk behavior,” says Aydogan. “In the brains of people who were more willing to take risks, we found less gray matter in these areas. How this gray matter influences behavior still has to be investigated. “
Insignificant influence of genes
The researchers also looked at the extent to which a possible genetic predisposition for risk behavior can be found in neuroanatomy. “It’s not easy to do,” says co-author Philipp Koellinger from the Free University of Amsterdam. “We know that most behavioral traits have a complex genetic architecture, with many genes that have small effects.” To counter this problem, the researchers developed a so-called polygenic risk index from a separate group of almost 300,000 people, for which they the Taking into account the effects of many genetic variations associated with risky behavior.
As the researchers found, however, only a small part of risk behavior could be linked to the genetic risk index. They also found associations with changes in brain anatomy in certain areas, but these only accounted for around 2.2 percent of the genetic disposition to risky behavior. According to the researchers, this suggests that the genes support risk behavior not primarily through their influence on the gray matter of the brain, but through other mechanisms. In addition, it is difficult to separate the influence of genes from environmental influences at all.
Nave emphasizes, “You have to remember that there are familial, environmental and genetic effects, and there is also the correlation between all of these factors. Even what appears to be a genetic effect could in reality be an educational effect because you inherit the genes of your parents and at the same time are shaped by their behavior. ”In further studies, the researchers want to investigate the interplay between genes, brain anatomy and behavior more closely . “Our ultimate goal is to untangle all of these relationships and identify the causal links,” says Nave.
Source: Gökhan Aydogan (University of Zurich) et al., Nature Human Behavior, doi: 10.1038 / s41562-020-01027-y