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Risk Preference and the NAcc

My Take

As most readers of EID probably know by now, I am fascinated by the neuropsychological basis of human behavior (for example just last week). We are just starting to understand the links and much of the research cannot be reliably applied (as some of our active commenters have made sure to remind me!). Even so, having an awareness of the latest neuro research is very helpful in framing what we see in human behavior and developing hypotheses for why it unfolds the way it does.

This study in Brain came from a team from the UK and Spain. They are studying the link between risk preference and the nucleus accumbens (NAcc). Even given the limitations in associating brain activity and human behavior that I acknowledged above, there is reasonable evidence that the NAcc is linked to risk preference. This study is remarkable in that they did a controlled study and the participants were blind to the intervention. This is rare in neuropsych studies where confounds and mediators are hard to control for.

Short-lived phasic electrical stimulation of the region of the nucleus accumbens dynamically altered risk behaviour, transiently shifting the psychometric function towards more risky decisions only for the duration of stimulation. A critical, on-line role of human nucleus accumbens in dynamic risk control is thereby established.

They used brain stimulation that was targeted just at the NAcc and they measured a baseline before stimulation, during stimulation, and after the stimulation was removed. Using a within-subjects design gives them a lot more sensitivity. The task was a series of gambles with varying levels of outcome probability and size of the reward. It was not loosely related by asking for perceptions of risk or predictions of expected behavior. This was tangible.

The results are telling. While the NAcc was stimulated, participants chose higher risk/reward gambles than they did during the baseline before stimulation, even as the total expected return (averaged across trials) was the same. When the stimulation was removed, their choices went back to the original. And remember, the participants were blind to if and when their NAcc was being stimulated.

You should notice the Signal Detection Theory approach to the method. The results show a shift in the decision criterion (Beta), not the sensitivity (d’). The changes were not better math skills or better understanding of risk. It was a difference in risk tolerance. When their NAcc was stimulated, they preferred gambles with more risk and more reward (and with equal expected return) than their baseline. When the stimulation was removed, their risk preference went back to baseline.

Looking at the shape of the curve reveals how this unfolds. It seems that the NAcc sets a fixed level for a person’s risk preference and he will look for the highest reward that does not exceed this level of risk. This is a much less cognitively intensive process than calculating expected returns for every option.

It also seems to reflect what we see in human factors and behavior science domains. When seat belts and airbags were introduced to cars, we saw drivers using more aggressive driving behaviors. How is this related? When you lower the risk without lowering the risk preference, the user can seek higher rewards. Driving more aggressively can save time. Many of my consulting projects in safety find the same thing out on the shop floor or in risky sites such as construction and maritime.

One limitation of the study is that they used participants who had underperforming NAccs. The stimulus brought the activation up to the level seen in the general population. This shouldn’t be too surprising either – we often see neuro interventions being effective at bringing injured/ill people up to a population standard, but not nearly as effective at moving a typical person up to a higher level. We saw that with memory, learning, and attention.

Your Turn

What do you think of this research and its conclusions? If you were frustrated by a low risk-tolerance, would you be willing to use brain stimulation to recalibrate yourself? Perhaps get you onto that roller coaster you have always been afraid of? Or could this wreak nightmares on our highways with more aggressive driving?

Or is it total bunk? Let us know.

Image Credit: aitoff

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