Study identifies neural circuits involved in making risky decisions.

As they go about their everyday lives, people often have to choose between a safe option and a riskier one, such as staying in a secure job, or starting a business, or buying a lottery ticket.  When the system of evaluating risk goes awry, it can have a severe impact on people’s lives. Maladaptive risk behaviours are a feature of compulsive gambling, bipolar disorder, anxiety and attention deficit hyperactivity disorder, to name a few.  Now, a study from researchers at Washington University School of Medicine in St. Louis pinpoints the brain region involved in decisions made under conditions of uncertainty, and identifies some of the cells involved in the decision-making process.  The team state that their findings could lead to treatments for psychiatric disorders which involve misjudging risk, such as problem gambling and anxiety disorders.  The study is published in The Journal of Neuroscience.

Previous studies show that the basal forebrain is thought to be a key brain area for the control of cognitive functions, such as learning and memory.  Learning and memory are known to be disproportionally shaped by surprising events or uncertain contexts as well as by other factors, such as the expectation of a reward or the fear of an aversive stimulus.  It has been shown from human imaging studies that the basal forebrain is more or less active in risk-seeking people, however, the neural circuits involved are largely unknown.  The current study identifies a population of value-coding neurons that are specifically suppressed when animals make a risky choice.

The current study utilised rhesus monkeys to investigate the neuronal circuits of risk-taking.  The animals were given a choice between a small amount of juice or a 50-50 chance of receiving either double that amount of juice or nothing at all. Over time, the amount of juice received under either condition would be the same, with one option safe and the other risky.

Results show that the basal forebrain contains at least two distinct neural-coding strategies to support this capacity; the dorsal-lateral basal forebrain, including the ventral pallidum, contains reward-sensitive neurons, some of which are selectively suppressed by uncertain-reward predictions. Data findings show, in contrast, the medial basal forebrain contains reward-sensitive neurons, some of which are selectively enhanced by uncertain-reward predictions.

The lab state that the monkeys chose the risky option more often than the safe option.  Data findings show that a group of value-coding neurons in the ventral pallidum were selectively suppressed when monkeys chose a risky option over a safe one. The group explain that the ventral pallidum plays an important role in controlling levels of dopamine, a molecule that transmits signals between neurons and makes us feel good.  They go on to add that the ventral pallidum inhibits dopamine neurons, and suppression of this area during risky behaviour may increase dopamine release.

The researchers also observed that neurons in the medial basal forebrain became most active after the monkeys made a risky choice, before they learned the outcome of their choice, juice or no juice. The lab explain that part of the brain provides inputs to a wide network of cortical brain regions involved in learning and memory.

The team surmise modulating the medial basal forebrain by uncertainty could promote or influence learning.  They are investigating whether temporarily turning off the ventral pallidum and the medial basal forebrain with targeted drug treatments affect the monkeys’ risk preferences and the strategies they use to learn.  For the future, the researchers state that there are no anatomically targeted treatments for psychiatric disorders associated with misjudging risk, such as pathological gambling and anxiety.  They conclude that now it is known where uncertainty is processed in the brain, the global medical community can start looking for ways to modulate it.

Source: Washington University School of Medicine in St. Louis