Fig. 2.

Endogenous fluctuations in SN/VTA BOLD activity modulate value-independent influences on choice. (A) Subjects (n = 43) gambled more when options were presented against a background of low compared to high endogenous SN/VTA activity. (B) This effect of greater risk taking for low than high activity was consistent across subjects. (C) The activity-induced shift in risk taking was independent of value with low endogenous activity leading to increased risk taking irrespective of option value. Differences in objective value between risky and safe options were divided into bins of equal sizes for each subject. (D) Choices were fitted to a parametric decision model based on prospect theory with the best-fitting model including a gambling bias parameter that was higher when endogenous activity was low. Positive gambling bias parameters reflects a tendency to take risks irrespective of option value. *P < 0.05 and ***P < 0.001. Data are mean ± SEM.