Dopamine D2 receptor reduction seems to decrease the capability of learning from errors. The sensitivity to negative action consequences is diminished. This may explain an increased risk for developing addictive behaviors in certain individuals. Addictive behavior can be seen as risk taking behavior. Individuals with A1-allele of the D2 dopamine receptor gene polymorphism are at risk. These carriers have a reduced dopamine D2 density in their posterior medial frontal cortex. They learn to avoid actions with negative consequences less efficiently. Many studies have found relations between a reduced dopamine D2 receptor density and addiction, obesity, or compulsive gambling.
Normally we learn from our mistakes. Positive outcome is a reinforcer and negative outcome should lead to avoidance of the erroneous behavior.
The performance monitoring system consists of:
1. Posterior medial frontal cortex (pMFC) signals the need for adjustment
2. The rostral cingulate zone (RCZ) of this location is involved in learning from errors
3. Dopaminergic neurons from the midbrain into this cingulate zone is involved in judging a situation as better or worse than expected
4. The basal ganglia in particular the nucleus accumbens (NAC) plays a role in reward based learning
5. Interaction with the hippocampal formation enables learning of stimulus-reward associations.
Method
26 healthy males grouped by 2 different genotypes of the polymorphism (A1 allele carries, n=12 and the non A1 allele carriers, n=14)under study were recorded with functional magnetic resonance imaging (fMRI). A learning task sensitive to dopaminergic manipulation was used.
The group with the A1-allele avoided the negative outcome significantly less, they also showed a reduced negative feedback related fMRI signal in the rostral cingulate zone.
The reward related activity increase in the nucleus accumbens was related to positive feedback as compared to negative feedback. This reward related increase was reduced in the A1-allele group in the right nucleus accumbens.
Article discussed:
Science. 2007 Dec 7;318(5856):1642-5.
Genetically determined differences in learning from errors.
Klein TA, Neumann J, Reuter M, Hennig J, von Cramon DY, Ullsperger M.
PMID: 18063800
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Wednesday, December 12, 2007
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