Background
Modulation of the serotonergic system affects long-term potentiation (LTP) and long-term
depression (LTD), the likely neurophysiologic derivates of learning and memory formation,
in animals and slice preparations. Serotonin-dependent modulation of plasticity has
been proposed as an underlying mechanism for depression. However, direct knowledge
about the impact of serotonin on neuroplasticity in humans is missing. Here we explore
the impact of the serotonin reuptake blocker citalopram on plasticity induced by transcranial
direct current stimulation (tDCS) in humans in a single-blinded, placebo-controlled,
randomized crossover study.
Methods
In 12 healthy subjects, anodal excitability-enhancing or cathodal excitability-diminishing
tDCS was applied to the motor cortex under a single dose of 20-mg citalopram or placebo
medication. Motor cortex excitability was monitored by single-pulse transcranial magnetic
stimulation (TMS).
Results
Under placebo medication, anodal tDCS enhanced, and cathodal tDCS reduced, excitability
for about 60–120 min. Citalopram enhanced and prolonged the facilitation induced by
anodal tDCS, whereas it turned cathodal tDCS-induced inhibition into facilitation.
Conclusions
Serotonin has a prominent impact on neuroplasticity in humans, which is in favor for
facilitatory plasticity. Taking into account serotonergic hypoactivity in depression,
this might explain deficits of learning and memory formation. Moreover, the results
suggest that for therapeutic brain stimulation in depression and other neuropsychiatric
diseases (e.g., in neurorehabilitation), serotonergic reinforcement may enhance facilitatory
aftereffects and thereby increase the efficacy of these tools.
Key Words
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Article info
Publication history
Published online: May 12, 2009
Accepted:
March 30,
2009
Received in revised form:
March 23,
2009
Received:
February 20,
2009
Identification
Copyright
© 2009 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.
