Cognitive deficits and striatal dopaminergic denervation in Parkinson's disease: a single photon emission computed tomography study using 123iodine-beta-CIT in patients on and off levodopa

Cognitive deficits affecting executive (frontal) functions have been widely described in Parkinson's disease (PD). However, dopa therapies are generally ineffective at reversing these deficits, except for tasks involving a sharing of attention such as working memory or simultaneous processing tasks. The aim of this study was to assess the relation between the nigrostriatal dopaminergic denervation in PD, as measured by SPECT with (123)Iodine-beta-CIT and the cognitive deficits, as measured by a simultaneous processing task, which had already been shown to be sensitive to dopa treatment. Ten patients with PD and ten control subjects were selected and matched for age, sex, and education. All subjects were assessed using computed visuo-auditory tasks which allow for the measurement of three cognitive processing conditions: 1) a Selective Processing Time; 2) a Competitive Processing Time; and 3) a Simultaneous Processing Time. Patients with PD were assessed both with (ON) and without (OFF) their usual dopaminergic treatment. The simultaneous processing condition but not the selective or the competitive conditions took significantly more time for patients with PD OFF than for either the control subjects or the patients with PD ON. In addition, when patients with PD were OFF, the simultaneous processing condition was correlated with the (123)Iodine-beta-CIT binding, but not when they were ON. These results suggest that nigrostriatal DA denervation may be involved in the specific impairment that patients with PD experience with simultaneous cognitive processing.