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Abstract:
Abstract: The role of dopamine in working memory performance,
which has been best studied in monkeys, has recently been
investigated via pharmacological challenge in humans.
Bromocriptine, a D-2 dopamine receptor agonist, has been found to
affect working memory performance in normal human subjects (Luciana
et al., 1998; Kimberg et al., 1997). Pergolide, a D-1/D-2 agonist,
has also been found to affect working memory (Muller, 1998).
However, direct evidence concerning the cortical effects of these
drugs has been lacking. In an earlier fMRI study, we found that
bromocriptine appeared to cause a general reduction in task-related
neural activity. In the present study, we used fMRI to compare
pergolide and bromocriptine directly, with the goal of identifying
and comparing their effects on patterns of neural activity evoked
by a simple working memory task. Subjects performed a delayed
response paradigm in the scanner on three occasions: on
bromocriptine, on pergolide, and on a placebo. We found evidence
for complex cortical effects on task-related neural activity for
both drugs. We also found evidence for both similarities and
differences in the net cortical effects of bromocriptine and
pergolide, assessed in task-related regions. We present findings
from both single subject and group analyses.
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