An experimental approach to examine behavior and brain activity during
decision-making under risk as compared to ambiguity
Abstract
Neural correlates of decisions under risk and under ambiguity have been
examined for several decades. In the current study, we focus on a
neglected aspect that is a potential confounding of the average risk of
alternatives in a trial, the average magnitude of the outcomes, and the
difference in risk between the two alternatives. We present an
experimental approach to solve this problem here and explicitly separate
risk and ambiguity. In the present fMRI-study with 20 participants, we
created different levels of risk and ambiguity to investigate their
effects on behavior and brain activation. In a first experimental block,
decisions with mixed-risk options (one high-risk option paired with one
low-risk option) were compared to decisions with two high-risk or two
low-risk options in terms of the effects on decision-making and neural
activity. The second block consisted of the same risk levels crossed
with high and low ambiguity by withholding information about the
probabilities of the outcomes. During mixed-risk trials participants
made cautious decision significantly more often. This effect was
strongest during mixed trials with high ambiguity in the second block.
In addition, risk behavior of subjects was correlated with the
subjective importance of the amount of potential monetary losses or wins
and the related probabilities. The fMRI results revealed activation of
the dorsal anterior cingulate cortex (dACC), the insula, and the
orbitofrontal cortex (OFC) during mixed risk trials without ambiguity.
In contrast, activation of the amygdala was specifically present during
mixed-risk trials with high ambiguity.