The effects of apomorphine on attentional processing in Parkinson's disease.

To ascertain whether variations in central dopaminergic transmission can differentially affect motor and cognitive processing, we studied the effects of apomorphine (APO) in 9 patients with Parkinson's disease (PD). The UPDRS motor scores and auditory event-related potentials (ERPs) obtained in the 'odd-ball' (OB) and in the 'covert orientation of attention' (COA) tasks were studied in the 'off' and in the 'on' state after an injection of APO. Although APO injection improved patients' motor status, it induced a significant increase in the latencies of the P2 and P3 ERP components in the OB. In the COA task, right-hand reaction times (RTs) were markedly shortened in the 'on' state while left hand RTs remained unchanged. The contrasting effects of dopaminergic stimulation on the motor performance and on some aspects of cognitive processing suggest the existence of complex interactions within pre- and postsynaptic brain dopamine receptors, and an intervention of segregated basal ganglia-prefrontal cortex loops in motor and cognitive behaviour.