Johnny Knoxville rides a "rocket_propelled" bike off a ramp in Jackass Two.
Everyone can learn from their mistakes — but some people have genes that may make it harder. That's the message from German researchers, writing in tomorrow's issue of the journal Science, who have shown how a common gene variant affects some people's ability to respond to, and learn from, the negative repercussions of their actions.
In a small study, the researchers scanned the brains of 26 men as they each performed a simple task: choosing one symbol from a pair of symbols. After each selection, the participant was presented with a smiley face or sad face, depending on the symbol he had chosen. All men were equally good at learning to pick the symbols that won them a smiley face, but some men were worse than others at avoiding the ones that resulted in sad faces. Those men, it turns out, had a particular gene variant, or allele, that reduces the density of receptors for dopamine — a neurotransmitter that plays a key role in motivation, pleasure and addiction — in certain areas of the brain. Brain scans also showed significantly less activity in those areas in response to the sad-faced negative feedback, in the men who had the allele. When it occurred, however, that brain activity was linked to activity in other parts of the brain that forms memories.
It's the first strong physiological evidence that the density of dopamine receptors may affect how people respond to negative inputs. Previous studies have established a strong link between a low density of dopamine receptors and addiction, obesity and compulsive gambling — conditions that suggest an impaired ability to learn from the consequences of bad decisions.
But the good news is that having the allele doesn't necessarily mean you can't learn from your mistakes. Although the men who had the genetic variant did show weaker responses to negative feedback, they did not perform markedly worse on the task at hand: They selected the good symbols from the bad about as often as participants who didn't have the allele. The results suggest that learning — though influenced by dopamine — is a complex process that involves much more than one kind of brain receptor. "It's just one factor that may contribute to some problems that might arise in some people," says Markus Ullsperger, a co-author of the Science paper, based at the Max Planck Institute for Neurological Research in Cologne. "I think you can compensate for many things without even noticing." In fact, a huge number of people have the genotype that Ullsperger studied, and never have trouble learning from their mistakes: About 30% of Europeans have the allele, according to the German researchers. (Comprehensive worldwide statistics don't exist.)
Like most scientific studies, the Science paper highlights what researchers don't yet know: the interplay of genes, dopamine and the process of learning is still mostly a mystery, and researchers are hesitant to guess how this particular genotype really affects any given individual — or that having it would even be a bad thing. "Under certain circumstances it might be positive [for a person] to ignore negative feedback and to persevere," says Ullsperger. Soldiering on in the face of setbacks, after all, is a key ingredient for success. In the end, these new findings may well be one of many steps toward piecing together the puzzle of learning.