Volume 16, Number 9,
Issue of May 1, 1996
pp. 3082-3088
Copyright ©1996 Society for Neuroscience
Covert Orienting of Attention in the Rat and the Role of
Striatal Dopamine
Received Nov. 26, 1995; revised Feb. 13, 1996; accepted Feb. 28, 1996.
Nick M. Ward and
Verity J. Brown
School of Psychology, University of St. Andrews, St. Andrews KY16
9JU, United Kingdom
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 recent progress has been made with the operational
definition of the processes involved in covert orienting. Reaction
times to visual targets are quickened when attention is drawn to the
location of the subsequent target, and processes such as disengagement,
maintenance, and movement of attention can be dissociated by using this
method. The possible involvement of striatal dopamine in covert
orienting is disputed, with conflicting reports of deficits in covert
orienting in patients with Parkinson's disease. To examine the
significance of dopamine in the striatum in attentional processes, a
test of covert orienting, analogous to that used in humans, was devised
for the rat. Unilateral dopamine-depleting lesions of the striatum
resulted in increases in mean reaction times contralateral to the side
of the lesion, but reaction times did not change differentially as a
function of the requirements to maintain, disengage, or shift
attention. These findings add additional support to the hypothesis that
the deficit that appears as hemineglect observed after striatal damage
reflects a motor impairment rather than damage in neural systems
underlying mechanisms for directing attention.
Key words:
striatum;
dopamine;
rat;
covert orienting;
attention;
Parkinson's disease