The effects of serotonin and catecholamine depletion on attentional control and response inhibition

The present study aimed to expand upon our knowledge of the role of brain monoamines on executive functioning by exploring the effects of serotonin depletion, dopamine depletion, and combined monoamine depletion, on attentional control and response inhibition. Ten healthy male participants completed the Stroop task under four treatment conditions; a) placebo control treatment, b) tryptophan depletion treatment, c) tyrosine/phenylalanine depletion treatment, and d) combined monoamine depletion treatment. The prediction that under tryptophan depletion there would be decreased Stroop interference and reaction times was not supported. However, the hypothesis that there would be no difference in the number of errors made under tryptophan depletion was supported. In addition, it was found that there was no difference in facilitation under tryptophan depletion. Concerning tyrosine/phenylalanine depletion, the predictions that there would be increased interference and reaction times, were not supported. However, the hypotheses that there would be no difference in facilitation or the number of errors made, were supported. Furthermore, under combined monoamine depletion, no difference in any of the Stroop task measures was observed. It was concluded that attentional control and response inhibition, as assessed by the Stroop task, are not affected by modulation of dopamine or serotonin with the use of amino acid depletion techniques.