Affective bias and response modulation following tyrosine depletion in healthy adults

Acute phenylalanine/tyrosine depletion (ATPD) has been used to transiently lower central nervous system dopamine activity in animals and humans. Findings suggest that ATPD may impact dopamine transmission in limbic and striatal regions. Impact on cognitive functions has varied across studies, although several recent reports suggest that affective processing in the context of a go/no-go response control task may be impaired during ATPD. In this study, response control under affective vs nonaffective conditions was examined in healthy individuals who underwent either ATPD or a balanced condition in a between-subjects design. Effects of ATPD were validated through its effects on serum prolactin secretion. ATPD resulted in significantly increased prolactin levels relative to the balanced mixture. Although there were no differences in self-reported mood between the groups, individuals in the ATPD condition demonstrated diminished sensitivity to positively valenced words and seemingly enhanced sensitivity to negatively valenced words in an affective go/no-go task. They also showed difficulties in modulating ongoing behavior in a nonaffective go/no-go task when responses had to be intermittently inhibited then immediately restarted. Basic motor functions were not impacted. Findings are discussed in relation to dopamine's role in switching signals within neural networks that are important for response modulation and affective control.