COVERT ORIENTING OF ATTENTION IN THE RAT AND THE ROLE OF STRIATAL DOPAMINE

Attention can be directed to a location in the absence of overt signs of orienting, a phenomenon termed ''covert orienting.'' The ability to orient attention covertly has been well documented in humans, but rec ent progress has been made with the operational definition of the proc esses involved in covert orienting. Reaction times to visual targets a re quickened when attention is drawn to the location of the subsequent target, and processes such as disengagement, maintenance, and movemen t of attention can be dissociated by using this method. The possible i nvolvement of striatal dopamine in covert orienting is disputed, with conflicting reports of deficits in covert orienting in patients with P arkinson's disease. To examine the significance of dopamine in the str iatum in attentional processes, a test of covert orienting, analogous to that used in humans, was devised for the rat. Unilateral dopamine-d epleting lesions of the striatum resulted in increases in mean reactio n times contralateral to the side of the lesion, but reaction times di d not change differentially as a function of the requirements to maint ain, disengage, or shift attention. These findings add additional supp ort to the hypothesis that the deficit that appears as hemineglect obs erved after striatal damage reflects a motor impairment rather than da mage in neural systems underlying mechanisms for directing attention.