Suppress the Urge: The Impact of L-Tyrosine on Behavioural and Neurophysiological Markers of Cognitive Control and the Role of Trait Impulsivity and Sensation-Seeking

Cognitive control refers to the ability to flexibly adapt mental processes to achieve goals by coordinating mechanisms like conflict monitoring, interference suppression, and response inhibition. Dopamine, synthesized in the ventral tegmental area and substantia nigra, modulates these processes via projections to the prefrontal cortex, striatum, and anterior cingulate cortex, supporting goal-directed behaviour. Disruptions in dopamine signaling impair inhibitory control, as observed in ADHD and Schizophrenia. The Dopamine Overdose Hypothesis proposes an inverted U-shaped relationship between dopamine and control, with trait differences in impulsivity and sensation-seeking shifting individuals along the curve, shaping inhibitory capacity. This study examined how the dopamine precursor L-tyrosine influences behavioural and neurophysiological markers of inhibitory control, and whether impulsivity and sensation-seeking moderate these effects. In a double-blind, between-subjects design,...Show moreCognitive control refers to the ability to flexibly adapt mental processes to achieve goals by coordinating mechanisms like conflict monitoring, interference suppression, and response inhibition. Dopamine, synthesized in the ventral tegmental area and substantia nigra, modulates these processes via projections to the prefrontal cortex, striatum, and anterior cingulate cortex, supporting goal-directed behaviour. Disruptions in dopamine signaling impair inhibitory control, as observed in ADHD and Schizophrenia. The Dopamine Overdose Hypothesis proposes an inverted U-shaped relationship between dopamine and control, with trait differences in impulsivity and sensation-seeking shifting individuals along the curve, shaping inhibitory capacity. This study examined how the dopamine precursor L-tyrosine influences behavioural and neurophysiological markers of inhibitory control, and whether impulsivity and sensation-seeking moderate these effects. In a double-blind, between-subjects design, 47 healthy adults received L-tyrosine or placebo and completed a Stroop task (reaction time, accuracy) while EEG recorded event-related potentials (ERP; N2, P300, N400). Impulsivity and sensation-seeking were assessed via the BIS-11 and SURPS “Sensation-Seeking” subscale. Behaviourally, higher sensation-seeking predicted reduced Stroop interference (faster responses), whereas higher impulsivity was associated with greater interference (slower responses). These patterns were not mirrored in accuracy, suggesting sensation-seekers favoured rapid responding, whereas impulsive individuals exhibited broader failures in control allocation, without accuracy costs. Impulsivity also moderated the item-specific proportion congruency effect, whereby highly impulsive participants responded particularly slowly under low-conflict conditions. Evidently, highly impulsive individuals exhibit deficits in both control allocation efficiency and conflict adaptation. L-tyrosine effects were trait-dependent: supplementation exacerbated interference in highly impulsive participants but did not significantly impact sensation-seekers. ERP analyses revealed P300 and N400 modulation by Congruency and Proportion congruency, but not Treatment, suggesting sensitivity to semantic integration and mismatch detection, rather than conflict per se. These findings highlight a multidimensional relationship between dopamine, personality traits, and inhibitory control, demonstrating that subtle dopamine interventions can have trait-dependent effects on inhibitory efficiency. Clinically, this underscores the importance of considering trait differences in interventions targeting dopamine-mediated processing, including pharmacological strategies for ADHD and schizophrenia. More broadly, this study emphasizes that personality traits shape both behavioural and neurophysiological responses to dopaminergic modulation and should be integrated into models of cognitive control.Show less

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Suppress the Urge: The Impact of L-Tyrosine on Behavioural and Neurophysiological Markers of Cognitive Control and the Role of Trait Impulsivity and Sensation-Seeking