A prevailing theory in neuroscience holds that people make decisions based on integrated global calculations that occur within the frontal cortex of the brain.

However, researchers have found that three distinct circuits connecting to different brain regions are involved in making good decisions, bad ones and determining which of those past choices to store in memory, they report in the journal Neuron.

The study of decision-making in rats may help scientists find the roots of flawed decision-making common to mental health disorders such as addiction, the authors say.

"Specific decision-making computations are altered in individuals with mental illness," said senior author of the study. "Our results suggest that these impairments may be linked to dysfunction within distinct neural circuits."

Researchers used a new tool to manipulate brain circuits in rats while they were making choices between actions that led to them receiving rewards or no rewards. The authors found decision-making is not confined to the orbital frontal cortex, seat of higher order thinking. Instead, brain circuits from the orbital frontal cortex connecting to deeper brain regions performed three different decision-making calculations.

Ablation of OFC neurons projecting to the nucleus accumbens selectively disrupted performance following a reversal, by disrupting the use of negative outcomes to guide subsequent choices. Ablation of amygdala neurons projecting to the OFC also impaired reversal performance, but due to disruptions in the use of positive outcomes to guide subsequent choices. Ablation of OFC neurons projecting to the amygdala, by contrast, enhanced reversal performance by destabilizing action values.

The lead author says an analogy would be deciding on a restaurant for dinner. If restaurant A has good food, one brain circuit is activated. If the food is bad, a different circuit is activated. A third circuit records the memories of the experience, good or bad. All three are crucial to decision-making.

For instance, without the "good choice" circuit you may not return to the restaurant with good food and without the "bad choice" circuit you might not avoid the restaurant with bad food. The third "memory" circuit is crucial in making decisions such as whether to return to the restaurant after receiving one bad meal after several good ones.

Alterations to these circuits may help explain a hallmark of addiction - why people continue to make harmful choices even after repeated negative experiences, researchers say.

The researchers previously showed that some of the same brain computations were disrupted in animals that had taken methamphetamine.

"Because we used a test that is equivalent to those used in studies of human decision- making, our findings have direct relevance to humans and could aid in the search for novel treatments for substance abuse in humans," the senior author said.

https://news.yale.edu/2019/06/25/how-brain-helps-us-make-good-decisions-and-bad-ones

https://www.cell.com/neuron/fulltext/S0896-6273(19)30495-7