Why do some older adults perform badly on the Iowa Gambling Task? A dissociation of OFC and DLPFC abilities in the ageing population
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The present study examines the performance of young (18-29 years) and older adults (55-85 years) on the Iowa Gambling Task (IGT). The main aim of this investigation was to ascertain whether the impaired performance exhibited by some older individuals resembles a poor pattern of performance associated with orbitofrontal cortex (OFC) dysfunction or whether it resembles a poor pattern of performance associated with dorsolateral prefrontal cortex (DLPFC) dysfunction. This was examined through the use of the Iowa Gambling Task and the shuffled Iowa Gambling Task. In addition to this, we aimed to detect any behavioural symptoms known to be associated with damage to these areas through the use of the Frontal Systems Behaviour Scale (FrSBe) self-rating questionnaire. We postulated that evidence of impairments in older individuals on these tasks may be used in support of the theories of disproportionate ageing within the prefrontal cortex. Our findings demonstrated that a subset of older adults performed disadvantageously on the IGT, indicated by their failure to shift their preference towards the safe decks as the game progressed. The performance profiles of the older individuals on this task indicated three distinct subgroups, namely ‘impaired’, ‘borderline’ and ‘unimpaired’, of varying performance. We concluded that impaired performance reflected orbitofrontal cortex abnormalities in older adults. The dorsolateral prefrontal cortex of the older participants failed to exhibit any abnormalities, demonstrated by their successful performance on the shuffled IGT. Although our FrSBe questionnaire failed to detect any significant differences in the behavioural symptoms of the older individuals, our findings provide strong support for theories of the vulnerability of the OFC to the negative effects of ageing.