Frontal-lobe mediated word retrieval in Parkinson's disease

Parkinsonians have been shown to have difficulty with executive functioning, which is mediated by the frontal lobes of the brain. Tests of verbal fluency have been used to evaluate frontal lobe dysfunction. Letter fluency, however, may require different processes and mechanisms than semantic fluency. Martin and colleagues (1994) found that letter fluency seemed to be mediated by the frontal lobes whereas semantic fluency seemed to be mediated by the temporal lobes. It follows that Parkinsonians would have difficulty with letter fluency tasks, given their problems with frontal lobe functions.

Differences between 30 Parkinsonian patients and 30 age-matched controls on both semantic and letter fluency tasks were examined and the relationship of performance on these tasks to executive function was evaluated. Results indicated that when executive functioning and depression are accounted for. Parkinsonians demonstrated poorer performance on letter but not category fluency relative to controls. Before accounting for depression and executive functioning, there were no differences between groups on letter fluency, however, controls performed significantly better than Parkinsonians on category fluency. Both category and letter fluency tasks correlated highly with a measure of executive function, the EXIT, but only for Parkinsonians. Screening for both executive impairment and depression are important when examining cognitive function in Parkinson's disease.