Prefrontal Cortex and Risk Taking

Human risk taking is characterized by a large amount of individual heterogeneity. In this study, we applied resting-state electroencephalography, which captures stable individual differences in neural activity, before subjects performed a risktaking task. Using a source-localization technique, we found that the baseline cortical activity in the right prefrontal cortex predicts individual risk-taking behavior. Individuals with higher baseline cortical activity in this brain area display more risk aversion than do other individuals. This finding demonstrates that neural characteristics that are stable over time can predict a highly complex behavior such as risk-taking behavior and furthermore suggests that hypoactivity in the right prefrontal cortex might serve as a dispositional indicator of lower regulatory abilities, which is expressed in greater risk-taking behavior. Some individuals are more likely to take risks than others are (Weber, Shafir, & Blais, 2004), resulting in important social and health consequences such as crime and substance use. There has been much work focusing on psychological characteristics that underlie individual differences in risk taking (for a review, see Reyna & Farley, 2006). However, no study has yet investigated whether neural dispositional determinants might explain this variability. Evidence from neuropsychology and neuroimaging suggests that the prefrontal cortex (PFC) is involved in risky-decision-making processes, raising the prospect that differences in the neural functioning of the PFC may explain individual differences in risk taking. Previous neuroimaging studies of risk taking, however, have focused on brain activity during the decision-making process, rather than examining individuals' pretask neurophysiological characteristics. Resting-state electroencephalography (EEG) is a method that measures the tonic cortical activity, i.e. the cortical activity before task performance. Various studies investigated the intraindividual stability of human EEG, revealing a stability over a period of years (e.g., Kondacs & Szabo, 1999). Thus, this method is able to capture dispositional individual differences. Patients with traumatic brain injuries or other pathologies affecting the PFC show a tendency for riskier, "out of character" decision making and an apparent disregard for negative consequences of their actions (Rahman, Sahakia, Cardinal, Rogers, & Robbins, 2001). This seems particularly true for patients with right-sided lesions (Clark, Manes, Antoun, Sahakian, & Robbins, 2003). In a previous study, we were able to manipulate risky decision making by modulating brain activity in the PFC by means of repetitive transcranial magnetic stimulation (rTMS), a technique that allows transient and noninvasive interference with cortical activity. Subjects displayed significantly riskier decision making after disruption of the right, but not the left, lateral PFC, choosing a larger potential reward even at a greater risk of penalty (Knoch et al., 2006). Resting EEG studies have shown that frontal hemispheric activation asymmetry in favor of the right PFC reflects a trait-like individual predisposition to respond in terms of withdrawalrelated behavior (e.g., Davidson, 2004; Harmon-Jones, 2004). These findings indicate that trait-like tendencies measured from resting asymmetry would be associated with an individual’s risk proneness, and that tonically decreased activity in the right PFC may predispose an individual to behave in a risky manner. METHOD Subjects Forty right-handed female students (mean age = 24.8 years, SD = 5.8 years) recruited at the University of Zurich participated in the study. We limited the sample to females to reduce possible sex-related variability in physiological responses, and righthanded subjects were selected to avoid physiological differences due to brain laterality (e.g., Davidson, Ekman, Saron, Senulis, & Friesen, 1990). All subjects were screened for health problems by using a detailed health questionnaire. They had no current or previous history of neurological or psychiatric disorder or alcohol or drug abuse. The local Ethics Committee approved the study. Subjects were remunerated with 30 Swiss francs for participating in addition to the money earned in the risk task.