Bipolar Research Today is a free monthly online journal that collates and summarizes the latest research about Bipolar, including details on bipolar disorder, symptoms, treatment, depression, medication.

Effect of acute tryptophan depletion on pre-frontal engagement.

Allen PP, Cleare AJ, Lee F, Fusar-Poli P, Tunstall N, Fu CH, Brammer MJ, McGuire PK

Division of Psychological Medicine P067, Institute of Psychiatry, De Crespigny Park, SE5 8AF, London, UK, p.allen@iop.kcl.ac.uk.

BACKGROUND: Serotonin is known to modulate cognitive functioning and has been implicated in the cognitive deficits associated with affective disorders. The present study examined regional brain activation during two tasks that are known to engage the pre-frontal cortex and are performed poorly by patients with depression and bipolar disorder. We tested the hypothesis that acute tryptophan depletion (ATD) would attenuate pre-frontal activation during both tasks. MATERIALS AND METHODS: Ten healthy right-handed volunteers were studied using functional MRI whilst performing a 2-back verbal working memory task and a phonological verbal fluency task. Subjects were studied in two separate sessions, after either a tryptophan-free or a balanced amino acid drink, in a double-blind design. Task performance and mood were measured online. RESULTS: Relative to sham depletion, ATD attenuated activation in the right superior frontal gyrus during the 2-back task and in the medial frontal gyrus and precuneus during the verbal fluency task. ATD lowered total plasma tryptophan by 79% but had no significant effect on either task performance or mood. CONCLUSIONS: The engagement of pre-frontal cortex during verbal working memory and verbal fluency tasks is significantly modulated by central serotonergic activity. The different location of these modulatory effects within the frontal cortex may reflect the engagement of distinct cognitive processes by the respective tasks.

Published 9 August 2006 in Psychopharmacology (Berl), 187(4): 486-97.
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