Effects of serotonin depletion and dopamine depletion on bimodal divided attention.

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:54 healthy adults (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 hours. Blood samples were taken before and 6 hours after challenge intake. RESULTS:Amino acid concentrations following challenge intake significantly decreased (all p ≤ .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 RT's (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 = .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. This is an Accepted Manuscript of an article published by Taylor & Francis in the World Journal of Biological Psychiatry on 08 October 2018, available online: http://www.tandfonline.com/10.1080/15622975.2018.1532110