Contributions of the dopaminergic system to voluntary and automatic orienting of visuospatial attention

Visuospatial attention can be directed by voluntary or involuntary control independent of eye movement. The involvement of cortical and subcortical neural structures in this covert orienting mechanism has been studied using neuroimaging and electrophysiological techniques. This study was designed to investigate the role of the dopaminergic system in both voluntary and automatic orienting mechanisms of visuospatial attention. We recorded event-related evoked potentials (ERPs) and reaction time (RT) during a cued priming task in both patients with idiopathic Parkinson's disease (PD) and control subjects. Voluntary and automatic shifts in attention were studied by using central and peripheral cues, respectively. In the experiment using a central cue, the RT data showed that when the cue-target interval was long, PD patients' responses were delayed, and cue validity effects were reduced, whereas in the peripheral cue experiment the validity effects persisted across all trials. The ERPs demonstrated reduced sustained negativities preceding the imperative targets in both the central and peripheral cue experiments in PD patients. Furthermore, during the long cue-target interval in the central cue experiment, PD patients showed reduced attention shift-related negativities (ARNs) at the anterior scalp sites, whereas ARNs were generated widely in the peripheral cue experiment. The ERP findings were consistent with the RT data. These findings suggest that the dopaminergic system may contribute to voluntary and sustained control of visuospatial attention as well as to the neural system for response preparation, whereas automatic control of visuospatial attention is relatively independent of the dopamine system.