Neurofunctional differences related to the Iowa Gambling Task in healthy older adults

The Iowa Gambling Task (IGT) is thought to model real-life decisions by factoring in reward, punishment, and uncertainty. Impairment on this task has been associated with circumscribed damage to the ventromedial prefrontal cortex (VMPC). Further, we have demonstrated that two groups of functionally and cognitively intact older adults show divergent behavioral performance (impaired versus unimpaired) on this task - a difference we hypothesize is attributable to disproportionate decline in the prefrontal cortex. To specifically test this hypothesis, sixteen IGT-impaired and sixteen IGT-unimpaired older adults performed an alternate version (K') of the IGT while in a functional magnetic resonance imaging scanner. We predicted that IGT-impaired older adults would have neurofunctional deficits in the prefrontal cortex relative to IGT-unimpaired older adults. In early blocks of the IGT, we observed greater activation among IGT-impaired older adults relative to IGT-unimpaired older adults in ventromedial prefrontal regions. In later blocks of the IGT, we observed greater activation among IGT-unimpaired older adults relative to IGT-impaired older adults in ventral prefrontal regions. These results are consistent with our original hypothesis that there may be disproportionate decline in the IGT-impaired older adults. On a broader scale, these results are consistent with the interpretation of a neural dissociation between decision-making under ambiguity (in the earlier blocks) and decision-making under risk (in the later blocks).