Effects of serotonin depletion and dopamine depletion on bimodal divided attention

Abstract

Objectives: This study aimed to explore the effects of acute phenylalanine tyrosine depletion (APTD) and acute tryptophan depletion (ATD) on bimodal divided attention. A balanced amino acid mixture (BAL) served as control condition.

Methods: Fifty-three healthy adults (final analyzed sample was N = 49, age: M = 23.8 years) were randomly assigned to APTD, ATD or BAL in a double-blind, between-subject approach. Divided attention was assessed after 4 h. Blood samples were taken before and 6 h after challenge intake.

Results: Amino acid concentrations following challenge intake significantly decreased (all P ≤ 0.01). There was a significant difference in the mean reaction time (RT) towards auditory stimuli, but not towards visual stimuli between the groups. Post-hoc comparison of mean RTs (auditory stimuli) showed a significant difference between ATD (RT = 604.0 ms, SD = 56.9 ms) and APTD (RT = 556.4 ms, SD = 54.2 ms; P = 0.037), but no RT difference between ATD and BAL or APTD and BAL (RT = 573.6 ms, SD = 45.7 ms).

Conclusions: The results indicate a possible dissociation between the effects of a diminished brain 5-HT and DA synthesis on the performance in a bimodal divided attention task. The difference was exclusively observed within the RT towards auditory signals.

Keywords:

• Acute tryptophan depletion
• phenylalanine tyrosine depletion
• serotonin
• dopamine
• attention

Acknowledgements

We would like to thank the IRTG 1328 (German Research Council [Deutsche Forschungsgemeinschaft, DFG]) for the support of the lead author, Werner Königschulte.

Statement of interest

The lead author (WK) was supported by the German Research Council (Deutsche Forschungsgemeinschaft DFG, IRTG 1328). FDZ was the recipient of an unrestricted award donated by the American Psychiatric Association (APA), the American Psychiatric Institute for Research and Education (APIRE) and AstraZeneca (Young Minds in Psychiatry Award). He has also received research support from the European Union, German Federal Ministry for Economics and Technology, the German Society for Social Pediatrics and Adolescent Medicine, the Paul and Ursula Klein Foundation, the Dr. August Scheidel Foundation, the IZKF fund of the University Hospital of RWTH Aachen University, the Telethon Perth Children’s Hospital Research Fund (TPCHR); the Princess Margaret Foundation, and a travel stipend donated by the GlaxoSmithKline Foundation. He is the recipient of an unrestricted educational grant, travel support and speaker honoraria by Shire Pharmaceuticals, Germany. In addition, he has received support from the Raine Foundation for Medical Research (Raine Visiting Professorship), and editorial fees from Co-Action Publishing (Sweden). GRF serves as an editorial board member of Cortex, NeuroImage: Clinical, Zeitschrift fu¨r Neuropsychologie and Fortschritte der Neurologie Psychiatrie; receives royalties from the publication of the book Funktionelle MRT in Psychiatrie und Neurologie and Neurologische Differentialdiagnose; received honoraria for speaking engagements from TEVA, GlaxoSmith-Kline, Bayer, Desitin, Infoforum and Boehringer Ingelheim; and received or receives research support from the Bundesministerium für Bildung und Forschung and the Deutsche Forschungsgemeinschaft. The other authors have nothing to disclose and no conflict of interest.

Additional information

Funding

This study was funded by the Excellence Initiative of the German federal and state governments.