Distractibility in early Parkinson's disease.

Post-mortem evidence has shown a depletion of dopamine in the mesocortical and mesolimbic pathways in brains of Parkinson patients. Since these dopaminergic pathways have been implicated in the control of attention in animals, selective attention to visual stimuli was studied in eight patients with early Parkinson's disease (Stage I or II as defined by the Hoehn and Yahr Scale) and eight normal controls of comparable age, sex and Full Scale Intelligence Quotient. Subjects with dementia, psychiatric disease and other neurological abnormalities were excluded. The Parkinson patients were more prone to interference in the presence of distractor items than the normal controls as shown on the focussing + distraction and switching + distraction of attention paradigms on the Distractor task. There findings are not accounted for by mood, intellectual status or memory and thus may be as a result of the loss of dopamine in the mesocortico-limbic projections.