Tryptophan depletion effects on EEG and MEG responses suggest serotonergic modulation of auditory involuntary attention in humans.

Full Abstract

Involuntary attention shifting, i.e., detecting and orienting to unexpected stimulus changes, may be altered at low brain serotonin (5-hydroxytryptamine; 5-HT) levels. This was studied in 13 healthy subjects (21-30 years old; 6 females) by using a dietary challenge, acute tryptophan depletion (ATD), which decreases 5-HT synthesis in the brain. Five hours after ingestion of either ATD or control mixture (randomized, double-blinded, crossover design), brain responses indexing involuntary attention were measured with simultaneous 64-channel electroencephalography (EEG) and 122-channel magnetoencephalography (MEG). During the measurement, the subjects were instructed to discriminate equiprobable 200- and 400-ms tones by pressing one of two buttons rapidly. Occasionally, the frequency of the tones changed (10% increase/decrease), causing involuntary attention shifting. ATD significantly lowered plasma tryptophan concentrations (total tryptophan decreased by 75%, free tryptophan decreased by 35%). As compared to the control condition, ATD reduced the amplitude of the deviant-tone N2 wave, including the overlapping mismatch negativity (MMN) and N2b subcomponents, which are suggested to reflect change detection in the brain. The EEG results were accompanied by a significant increase in the peak latency of the magnetic counterpart of MMN. However, no ATD effects were observed in P3 to task-irrelevant frequency change. Reaction time (RT) to deviants per se was not significantly affected, but RT in trials succeeding the deviant-frequency tones was increased by ATD, which suggested impaired reorienting to the task-relevant activity. In conclusion, the results suggest that decreased level of central 5-HT function after ATD may decrease involuntary attention shifting to task-irrelevant sound changes and thus modulate resource allocation to the task-relevant activity.

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Author information

Author/s: Ahveninen, Jyrki (J); Kähkönen, Seppo (S); Pennanen, Sirpa (S); Liesivuori, Jyrki (J); Ilmoniemi, Risto J (RJ); Jääskeläinen, Iiro P (IP);

Affiliation: Cognitive Brain Research Unit, Department of Psychology, P.O. Box 13, University of Helsinki, Helsinki, FIN-00014, Finland.

Journal and publication information

Publication Type: Clinical Trial; Journal Article; Randomized Controlled Trial; Research Support, Non-U.S. Gov't

Journal: NeuroImage (Neuroimage), published in United States. (Language: eng)

Reference: 2002-Aug; vol 16 (issue 4) : pp 1052-61

Dates: Created 2002/08/30; Completed 2002/10/09; Revised 2006/11/15;

PMID: 12202092, status: MEDLINE (last retrieval date: 12/26/2008)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Acoustic Stimulation - methods
Adult
Attention - physiology
Auditory Perception - physiology
Cross-Over Studies
Double-Blind Method
Electroencephalography
Female

Humans
Magnetoencephalography
Male
Reaction Time
Reference Values
Serotonin - physiology
Tryptophan - blood; deficiency
Volition

Associated Chemicals: Serotonin (50-67-9) ; Tryptophan (73-22-3)

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