Wednesday, December 21, 2005

Genetic determination of brain responses

The trends in brain imaging are turning towards the study of genes in order to better understand individual differences. While much brain recording to date has been focusing on similarities between people, and what differs between groups, new approaches are looking at what produces the individual differences seen in neuroimaging studies. Some of this variation can be explained by influences of genes, and how each individual's brain is built.

Some of the recent findings have been that the genetic polymorphism -- a normal variance in people -- in the seretonin system has an impact on how people's brain react to emotional pictures. In other words, if Kyle has a type A seretonin gene and Paul has type B, Kyle's brain will react more strongly to emotional faces than Paul. In this sense, it has been shown that even within a healthy sample of people, individual differences can be predicted on the basis of the genetic makeup.

In a recently published study by Cohen et al. this same approach is used to determine individual differences in the dopamine system. Here, Cohen and colleagues find that both the genetic makup of the dopaminergic brain system and the level of extraversion (a personality trait) determines individual differences in the brain's reaction to reward in a gambling game.

As such, these studies clearly demonstrate the importance of the genotype in neuroimaging studies. As I wrote in the previous post, evolution operates at the molecular level. Genes operate at the level of proteins in the brain. We do not understand this properly yet, but with the advent of imaging genetics, this issue is being put at the forefront of neuroscience.

Individual differences in extraversion and dopamine genetics predict neural reward responses

Cohen et al in Cognitive Brain Research

Psychologists have linked the personality trait extraversion both to differences in reward sensitivity and to dopamine functioning, but little is known about how these differences are reflected in the functioning of the brain's dopaminergic neural reward system. Here, we show that individual differences in extraversion and the presence of the A1 allele on the dopamine D2 receptor gene predict activation magnitudes in the brain's reward system during a gambling task. In two functional MRI experiments, participants probabilistically received rewards either immediately following a behavioral response (Study 1) or after a 7.5 s anticipation period (Study 2). Although group activation maps revealed anticipation- and reward-related activations in the reward system, individual differences in extraversion and the presence of the D2 Taq1A allele predicted a significant amount of inter-subject variability in the magnitudes of reward-related, but not anticipation-related, activations. These results demonstrate a link between stable differences in personality, genetics, and brain functioning.



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