Tryptophan depletion in normal volunteers produces selective impairments in learning and memory.
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.
Park
S B
SB
MRC Psychopharmacology Unit, University of Oxford, Littlemore Hospital, U.K.
Coull
J T
JT
McShane
R H
RH
Young
A H
AH
Sahakian
B J
BJ
Robbins
T W
TW
Cowen
P J
PJ
D000328:Adult; D000596:Amino Acids / Q000097:blood / Q000494:pharmacology; D001923:Brain Chemistry / Q000187:drug effects; D003071:Cognition / Q000187:drug effects; D018592:Cross-Over Studies; D004192:Discrimination, Psychological / Q000187:drug effects; D006801:Humans; D007859:Learning Disabilities / Q000378:metabolism* / Q000523:psychology; D008297:Male; D008569:Memory Disorders / Q000378:metabolism* / Q000523:psychology; D008606:Mental Processes / Q000187:drug effects; D009483:Neuropsychological Tests; D010364:Pattern Recognition, Visual / Q000187:drug effects; D013028:Space Perception / Q000187:drug effects; D014364:Tryptophan / Q000172:deficiency*
D000596:Amino Acids; D014364:Tryptophan