This supporting material provides detailed information about the methodology, behavioral data analysis, fMRI acquisition, and analysis, as well as lesion patient data and related literature. The study involved 16 Caltech undergraduate and graduate students who participated in three treatments: Card-Deck, Knowledge, and Informed Opponents. Each treatment included 48 trials, with 24 ambiguous and 24 risky choices. The behavioral task was conducted using MRI-compatible goggles and buttons, and subjects were allowed to make choices at their own pace. The fMRI analysis used a general linear model to identify brain regions sensitive to ambiguity and risk, with a focus on the dorsal striatum, amygdala, and OFC. Lesion patient data from 12 neurological patients were also analyzed to assess the impact of brain lesions on ambiguity and risk aversion. The study found that the dorsal striatum was activated more during risky than ambiguous choices, and that ambiguity aversion was associated with higher levels of certain payoff choices. The results highlight the neural mechanisms underlying decision-making under uncertainty and risk.This supporting material provides detailed information about the methodology, behavioral data analysis, fMRI acquisition, and analysis, as well as lesion patient data and related literature. The study involved 16 Caltech undergraduate and graduate students who participated in three treatments: Card-Deck, Knowledge, and Informed Opponents. Each treatment included 48 trials, with 24 ambiguous and 24 risky choices. The behavioral task was conducted using MRI-compatible goggles and buttons, and subjects were allowed to make choices at their own pace. The fMRI analysis used a general linear model to identify brain regions sensitive to ambiguity and risk, with a focus on the dorsal striatum, amygdala, and OFC. Lesion patient data from 12 neurological patients were also analyzed to assess the impact of brain lesions on ambiguity and risk aversion. The study found that the dorsal striatum was activated more during risky than ambiguous choices, and that ambiguity aversion was associated with higher levels of certain payoff choices. The results highlight the neural mechanisms underlying decision-making under uncertainty and risk.