Frontal brain injury alters human risky choices in self and other contexts.

Frontal lobe integrity is crucial for risky decision-making. We investigated how frontal lesions affect computational mechanisms underlying risk when decisions impact oneself versus others. Twenty patients with frontal damage and 20 matched controls accepted or rejected mixed-outcome gambles for themselves or an anonymous other. Patients accepted more disadvantageous gambles than controls in the self condition and showed greater caution for another person; controls showed no self-other difference. Formal model comparison favored a four-parameter Prospect Theory model. Relative to controls, patients showed near-linear probability weighting, reduced loss aversion, and steeper utility curvature; counterfactual analysis identified reduced loss aversion as the principal driver of increased acceptance of disadvantageous gambles. Parameter differences were consistent across conditions; the behavioral dissociation was not reflected computationally. Lesion overlap revealed heterogeneous frontal damage with common ventral and medial prefrontal involvement. These findings provide a mechanistic account of how frontal damage produces dissociable decision patterns across social contexts.