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Abstract:
Abstract: The noradrenergic system has been widely implicated
in the modulation of attention and arousal. We examined whether the
reported1 noradrenergic reduction of the beneficial effect of a
warning cue (alerting effect) results from an effect on orienting
toward a particular point in time (temporal orienting). Ten healthy
volunteers received placebo or 200μg clonidine (α2
adrenoceptor agonist) in a within-subjects design. Subjects were
scanned with fMRI while performing attentional orienting tasks
containing spatially-informative (left or right),
temporally-informative (short or long cue-target interval), neutral
or no cues. Behaviourally, clonidine impaired the alerting effect
(slowed neutral but not no-cue trials), slowed RTs to unexpectedly
delayed targets in the temporal orienting task, and speeded RTs to
invalidly-cued targets appearing in left visual field in the
spatial orienting task. Neuroanatomically, clonidine attenuated
activity in left superior parietal cortex during both spatial and
temporal orienting, but in left inferior parietal cortex during
alerting. Therefore, the noradrenergic modulation of attentional
orienting is mediated via left superior parietal cortex in both
spatial and temporal domains. Furthermore, the dissociation in
inferior/superior parietal cortex effects suggests that the
noradrenergic modulation of the alerting effect does not result
from an effect on temporal orienting. Witte and Marrocco (1997)
Psychopharmacology: 132:315-323
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