Wednesday, December 26, 2007

Learning from errors - genetic differences between humans

From Holden's brief summary of the work:
"Once burned, twice shy" works for most people. But some people are slow to learn from bad experiences.
This work shows that:
...people with a particular gene variant have more difficulty learning via negative reinforcement.
...demonstrates that a single-base-pair difference in the genome is associated with a remarkably different ability to learn from past mistakes is quite an accomplishment
...combines brain imaging with a task in which participants chose between symbols on a computer screen,
...centers on the A1 variant, or allele, of the gene encoding the D2 receptor, a protein on the surface of brain cells activated by the neurotransmitter dopamine. Earlier studies have hinted that this variant alters the brain's reward pathways and thereby makes people more vulnerable to addictions.
Brain activity was monitored (color) as a subject chose between two symbols (inset) and was rewarded with a smiley or frowny face. In the left panel the lower colors are hippocampus, the upper one the posterior medial frontal cortex.

Here is the abstract from Klein et al.
The role of dopamine in monitoring negative action outcomes and feedback-based learning was tested in a neuroimaging study in humans grouped according to the dopamine D2 receptor gene polymorphism DRD2-TAQ-IA. In a probabilistic learning task, A1-allele carriers with reduced dopamine D2 receptor densities learned to avoid actions with negative consequences less efficiently. Their posterior medial frontal cortex (pMFC), involved in feedback monitoring, responded less to negative feedback than others' did. Dynamically changing interactions between pMFC and hippocampus found to underlie feedback-based learning were reduced in A1-allele carriers. This demonstrates that learning from errors requires dopaminergic signaling. Dopamine D2 receptor reduction seems to decrease sensitivity to negative action consequences, which may explain an increased risk of developing addictive behaviors in A1-allele carriers.

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