Neuroanatomical Substrates for Risk Behavior

Abstract

Individuals vary substantially in their tendency to take risks. In the past two decades, a large number of neuroimaging studies in humans have explored the neural mechanisms of several cognitive processes that contribute to risk taking. In this article, I focus on functional and structural MRI studies that investigated uncertainty processing, one of the main features of risk behavior. Using decision-making and learning paradigms, these studies implicated a network of brain areas, including posterior parietal cortex, anterior insula, anterior cingulate cortex, and ventrolateral prefrontal cortex, in various aspects of uncertainty processing. Individual differences in behavior under uncertainty are reflected in the function and structure of some of these areas and are integrated into value representations in ventromedial prefrontal cortex and ventral striatum, reinforcing the potential contribution of all of these brain structures to individual tendencies to take risks.

Keywords: ACC; PPC; ambiguity; functional MRI; risk taking; structural MRI; uncertainty; ventral striatum vmPFC; vlPFC; vmPFC.

Figure 1.

A schematic representation of central brain areas involved in risk taking behavior. ACC, anterior cingulate cortex; AI, anterior insula; DLPFC, dorsolateral prefrontal cortex; OFC, orbitofrontal cortex; PPC, posterior parietal cortex; vlPFC, ventrolateral prefrontal cortex; vmPFC, ventromedial prefrontal cortex; VS, ventral striatum.

Figure 2.

Examples of stimuli used to elicit risk attitudes. (A) Betting on whether the second of two consecutively presented cards will be higher or lower (adapted from Preuschoff et al, 2006). (B) Presentation of stimuli that were previously associated with outcomes of particular magnitudes and probabilities (adapted from Tobler et al, 2007). (C) Choice between a lottery and a certain amount. The lottery could be of varying outcome probability (left) and magnitude (adapted from Gilaie-Dotan et al, 2014).

Figure 3.

Risk and subjective value as a function of outcome probability. While subjective value increases monotonically with reward probability, risk first increases and then decreases. This can be used to distinguish between neural encoding of probability (or value) and neural encoding of risk.

Figure 4.

A region in right posterior parietal cortex (PPC) predicts individual risk attitudes. (A) Exploratory analysis. Left: whole-brain VBM revealed a single brain region whose volume correlates with individual risk tolerance. Right: illustration of the association between gray-matter volume and risk tolerance. (B) Confirmatory analysis in an independent group of subjects. The gray-matter volume from the region identified in the exploratory analysis predicted risk attitudes in the new sample (left), while gray-matter volume from a control area did not (right).

Figure 5.

Subjective probability. When probability information is explicitly conveyed, low probabilities are typically overestimated, whereas high probabilities are underestimated.

Figure 6.

Stimuli used to elicit ambiguity attitudes. (A) Complete ambiguity. Comparison of ambiguity with no ambiguity. Top: adapted from Hsu et al, 2005; Bottom: adapted from Huettel et al, 2006. (B) Partial ambiguity. By occluding part of a risky lottery, some of the information about outcome probability is withheld, creating partial ambiguity (adapted from Gilaie-Dotan et al, 2014).