A new study from the Massachusetts Institute of Technology has revealed that a group of neurons in the brain’s striatum encode information about the potential outcomes of different decisions. The study was published in the journal “Nature Communications”.
A group of neurons in the brain become particularly active when a behavior leads to an outcome different from what was expected, which the researchers say helped the brain adapt to changing circumstances. “A lot of this brain activity deals with surprising outcomes because if an outcome is expected, there’s really nothing to learn. What we’re seeing is that there’s a strong encoding of unexpected rewards and unexpected negative results,” said Bernard Bloem, an MIT Postdoc and one of the new study’s lead authors.
Impairments in this type of decision-making are a feature of many neuropsychiatric disorders, particularly anxiety and depression. The new findings suggest that slight disturbances in the activity of these striatal neurons could cause the brain to make impulsive decisions or become paralyzed by indecision, the researchers said. The striatum, located deep in the brain, is known to play a key role in making decisions that require evaluating the results of a particular action. In this study, the researchers wanted to learn more about the neural basis of how the brain makes cost-benefit decisions, in which a behavior can have a mix of positive and negative outcomes.
To study this type of decision-making, the researchers trained mice to spin a wheel left or right. Each round, they received a combination of a reward (sweet water) and a negative result (a small puff of air). As the mice performed the task, they learned to maximize reward delivery and minimize puff delivery. However, over hundreds of trials, the researchers frequently changed the odds of getting the reward or the puff of air, so the mice had to adjust their behavior.
As the mice learned to make these adjustments, the researchers recorded the activity of striatal neurons. They expected to find neural activity that reflects which actions are good and should be repeated, or bad and should be avoided. While some neurons were doing this, the researchers also discovered, to their surprise, that many neurons were encoding details about the relationship between actions and the two types of outcomes. The researchers found that these neurons responded more strongly when a behavior led to an unexpected outcome, that is, when turning the wheel in one direction produced the opposite result than in previous trials. These reward and penalty “error signals” seem to help the brain know it’s time to change tack.
Most of the neurons that encode these error signals are found in striosomes – groups of neurons located in the striatum. Previous work has shown that striosomes send information to many other parts of the brain, including dopamine-producing regions and regions involved in movement planning. “Striosomes seem to mostly follow actual results,” Bloem said.
“The decision whether or not to do an action, which essentially requires the integration of multiple outcomes, probably happens somewhere downstream in the brain,” he added. The results could be relevant not only to mice learning a task, but also to many decisions people have to make every day when weighing the risks and benefits of each choice. Eating a big bowl of ice cream after dinner provides immediate gratification, but it can contribute to weight gain or poor health. Deciding to have carrots instead will make you feel healthier, but you’ll miss out on the sweet treat.
“From a value perspective, these can be considered just as good,” Bloem said. “What we’re finding is that the striatum also knows why they’re good, and it knows what the benefits and cost of each are. In a way, the activity there is much more reflective of the potential outcome. than the likelihood of you choosing that,” he added.
This type of complex decision-making is often impaired in people with various neuropsychiatric disorders, including anxiety, depression, schizophrenia, obsessive-compulsive disorder, and post-traumatic stress disorder. Drug abuse can also lead to impaired judgment and impulsiveness. “You can imagine that if things were set up that way, it wouldn’t be so hard to confuse what’s good and what’s bad, because there are neurons that fire when an outcome is good and they fire also when the outcome is bad,” said Ann Graybiel, a professor at the MIT Institute.
“Our ability to make our movements or our thoughts what we call a normal way depends on those distinctions, and if they blur, that’s a real problem,” she added. The new findings suggest that behavioral therapy targeting the stage at which information about potential outcomes is encoded in the brain could help people with these disorders, the researchers said. (ANI)
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