Acute Serotonin and Dopamine Depletion Improves Attentional Control: Findings from the Stroop Task

Abstract

Schizophrenia is associated with impairments of attentional control on classic experimental paradigms such as the Stroop task. However, at a basic level the neurochemical mechanisms that may be responsible for such impairments are poorly understood. In this study, we sought to investigate the influence of brain monoamine function on Stroop task performance in healthy participants using the established methods of acute dietary serotonin, dopamine, and combined monoamine depletion. The study was a double-blind placebo controlled design in which 12 healthy male participants completed the Stroop task under four acute treatment conditions: (a) balanced/placebo control, (b) acute tryptophan depletion, (c) acute tyrosine/phenylalanine depletion, and (d) acute tyrosine/phenylalanine/tryptophan depletion (combined monoamine depletion). Decreased Stroop interference indicating improved attentional control was observed after both tryptophan depletion and tyrosine/phenylalanine depletion, while there was no significant change in interference after combined monoamine depletion. Findings suggest that reduced tonic dopamine or serotonin activity within specific neural circuits (such as the striatum, anterior cingulate, or prefrontal cortex) may play a critical role in attentional control, possibly by improving gating of information via reducing noise in monoaminergic systems. These findings enhance our understanding of the neurochemical basis of attentional control and the possible cause of attentional control deficits in schizophrenia.

Serotonin Depletion Induces ‘Waiting Impulsivity’ on the Human Four-Choice Serial Reaction Time Task: Cross-Species Translational Significance

“…These findings suggest that serotonin loss enhances salience of stimuli associated with reward as in the case of both the rodent and human 5-CSRTT. This general conclusion appears valid for the effects of TD in other test situations in humans, as, for example, TD-enhanced performance in Stroop test (Scholes et al, 2007). A further effect of TD in the human 4-CSRTT was to increase a 'motivational index', which was derived from the difference in RT of baseline test blocks separated by the block where error feedback was provided.…”

Acute dopamine and/or serotonin depletion does not modulate mismatch negativity (MMN) in healthy human participants

“…Acute tyrosine/phenylalanine depletion (ATPD) has been shown to selectively decrease DA synthesis and release (Leyton et al 2004;McTavish et al 1999aMcTavish et al , b, 2001aMehta et al 2005;Montgomery et al 2003), and impair DA-dependant cognitive processes such as working memory (Harmer et al 2001;Harrison et al 2004). Finally, CMD has been shown to simultaneously deplete tryptophan, tyrosine and phenylalanine to levels that are expected to modulate central serotonergic and dopaminergic function ) and modulate cognitive and sensory processes related to 5-HT and DA functions Scholes et al 2007;Mann et al 2008).…”

Acute tryptophan depletion in humans: a review of theoretical, practical and ethical aspects

“…Harrison and colleagues 64 demonstrated that ATD but not APTD impaired declarative memory in healthy women. Scholes and colleagues 65 found that ATD and APTD, but not the combined depletion, decreased Stroop interference in healthy men, indicating increased attentional control. Finally, Mann and colleagues 66 studied healthy men who showed disruption of prepulse inhibition after ATD, but not after APTD.…”