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' states following APO injection. Although APO injection improved the patients motor status, it induced a significant increase in latencies of the P2 and P3 ERP components in the OB task. In the COA task, right-hand reaction times (RTs) were markedly shortened during the 'on' state while left hand RTs remained unchanged. The contrasting effects of dopaminergic stimulation on 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.

Keywords: Apomorphine, covert orienting of attention, event-related potentials, Parkinson