Researchers have identified a small group of nerve cells in a specific brain region of rats whose signaling activity, or lack of it, explains the vast bulk of differences in risk-taking preferences among the animals, according to a study published online Wednesday in the journal Nature.
Risk-preference varies across individuals and within an individual from time to time, but the source of this variability in the brain is not known. D2R (Dopamine receptor type-2)-expressing cells may have a role in regulating risky decisions.
A team of researchers at Stanford University developed a model of risk-seeking in rats that parallels human behavior and showed that D2R-expressing cells within the nucleus accumbens drive risk-preference.
When rats were presented with a choice between a "safe" lever that consistently delivers a small amount of sucrose reward or a "risky" lever that inconsistently delivers either a large reward (the more favorable outcome) or nothing (the less favorable outcome), the D2R-expressing cells signaled the less favorable outcome of a previous choice at an appropriate time during the decision period.
This signal was higher in risk-averse animals than in risk-seeking animals and predicted whether, on the subsequent trial, a rat would choose the safe or risky option, according to the study.
The authors also showed that optogenetic (light-mediated) stimulation of the D2R neurons during the decision period decreased risky choices in risk-seeking rats, but not in rats that were already risk-averse.
The findings expand on noninvasive research conducted previously in humans. "Humans and rats have similar brain structures involved," said Prof. Karl Deisseroth from Stanford University, who is one of the study authors.
"It looks as though we have found a brain signal that, in most individuals, corresponds to a memory of a failed risky choice," said Deisseroth. "It seems to represent the memory of that recent unfavorable outcome, manifested later at just the right time when it can, and does, modify an upcoming decision."
