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The neurobiology of risk: the posterior cingulate cortex

The cingulate cortex sits on top of the corpus callosum, the thick cable that connects the two halves of the brain. It’s connected with the amygdala, which coordinates perceptions of feeling and emotion, and divided into the anterior and posterior parts. The anterior cingulate cortex has been implicated in effortful decision-making (Mulert et al., 2008, Neuroimage), and the posterior cingulate cortex (PCC), relatedly, in decision-making and risk.

Decision-making and risk are important parts of the animal world; any organism needs to know whether a particular activity is going to get it killed, and decide whether that activity is worth it. Watson (2008, Annals of the New York Academy of Sciences) suggests that sensitivity to risk helps animals survive. The PCC hasn’t been studied much until recently, but it’s possible that it’s the center for risk-related brain activity.

Watson found that the PCC in monkeys showed sensitivity to risk, and its strength, in decision-making tasks. McCoy and Platt (2005, Nature Neuroscience) found that PCC in monkeys activated when monkeys made risky choices, and became more active with more perceived risk.

This article describes how the PCC judges value of rewards as circumstances change. Researchers (Platt et al., 2003) trained monkeys to do a task and rewarded it with juice, so that the monkey learned to expect the juice when it delivered. When the monkey performed the task but got no juice, the PCC fired very strongly, giving what the researchers described as a large “reward-prediction error,” a comparison of a predicted reward with the actual result. This isn’t specifically risk-related, but it does demonstrate that awareness of rewards and their absence is important–otherwise there wouldn’t be a segment of the brain devoted to it. And risk is all about evaluating reward.

Perhaps the main thing to take away from the neurobiology of risk is that it’s inextricably tied into emotion. The PCC, like the ventral striatum, contains dopamine-releasing neurons, and it’s also part of the limbic system, which regulates emotion and motivation. And fear, which may be particularly important in the PCC–learned fear may be stored there–regulates risk-taking behavior and perceptions of risk in general. This, too, makes sense; it doesn’t really matter what the objective risk of a given activity–darting into the open to get that delicious plant, say, or using $100 to buy stock in Google rather than putting it in the bank–actually is if you don’t have some emotional investment in the outcomes.

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