Attention and executive deficits in PD are most often ascribed to frontal lobe dysfunction secondary to striatofrontal deafferentation and, in particular, pathophysio-logical alterations in the basal ganglionic-dorsolateral frontal loops with medial nigral dopamine depletion impacting the caudate and its frontal projections (31). Performance on simple tasks of attention, for example, forward digit span, is most often preserved in patients with PD (32). On the other hand, deficits on tasks, requiring complex attention, planning, reasoning, abstraction, conceptualization, and cognitive flexibility, are more readily identified in PD. Deficits are most apparent on tasks that require spontaneous, self-directed information, processing strategy formulation and deployment (33). Executive dysfunction may account for some of the deficits observed on recall, verbal fluency, and visuoperceptual tasks (34), but it is unlikely that executive deficits alone can explain the range of cognitive changes observable in PD (35,36).
Observations of executive dysfunction in PD are increasingly accompanied by functional neuroimaging data that permit a clearer understanding of these deficits' neural correlates. Positron emission tomography studies have shown reduced blood flow in the globus pallidus (37), the caudate, and the dorsolateral frontal cortex of PD patients compared with controls in response to activation with the Tower of London task (38). Performance on the Tower of London task is improved by levodopa administration, and this improvement is accompanied by normalization of dorsolateral frontal cortex blood flow relative to healthy elderly.
Given recent concern about pathological gambling among patients taking dopamine agonists (39), studies of decision making during a gambling task may provide important insights into this phenomenon. One gambling task evaluating decision making, judgment, and impulsivity is that of Bechara et al. (40). Examinees are instructed to maximize their gambling winnings by choosing cards from different decks, which yield either a high payoff (coupled with high risk), or low payoff at low risk. The low payoff, low-risk decks are designed to yield net winnings in the long term, whereas the high payoff, high-risk decks yield losses. Czernecki et al. (41) found that PD patients' performance on the gambling task did not improve across assessments, suggesting a failure to benefit from experience. Consistent with the clinical association between dopaminergic treatment and pathological gambling, another study (42) found that deficits on the gambling task may only be observable when patients are on dopaminomimetic medications.
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