Tryptophan depletion in normal volunteers produces selective impairments in learning and memory.

Journal article

The amino-acid L-tryptophan is essential in the synthesis of brain serotonin, and its depletion can lead to a widespread reduction in central serotonergic activity. A placebo-controlled cross-over within-subjects design (n = 12) examined the effects of tryptophan depletion on human cognitive performance. A low-tryptophan (low-TRP) drink successfully reduced the levels of plasma and total free tryptophan. Computerized tests of memory, learning and executive function revealed selective and non-sedative impairments on cognitive performance following the active drink. Specifically, low-TRP impaired learning as seen in tests of visual discrimination and paired associates. Furthermore, low-TRP lengthened thinking times during the Tower of London planning task, but only in subjects already familiar with the task, suggesting a retrieval deficit. No evidence was found for an effect of the low-TRP drink on measures sensitive to frontal lobe dysfunction, supporting instead a specific role for the serotonergic system in the processes of memory and learning not directly implicated in frontal lobe function.

Authors: Park, S; Coull, J; McShane, R; Young, A; Sahakian, B

• Publication status: Published
• Journal: Neuropharmacology
• Volume: 33
• Issue: 3-4
• Pages: 575-588
• Publication date: 1994-03-01
• DOI: 10.1016/0028-3908(94)90089-2
• EISSN: 1873-7064
• ISSN: 0028-3908
• Language: English
• Keywords: Cognition; Brain Chemistry; Humans; Adult; Mental Processes; Discrimination (Psychology); Male; Neuropsychological Tests; Pattern Recognition, Visual; Cross-Over Studies; Space Perception; Learning Disorders; Tryptophan; Memory Disorders; Amino Acids