GABAergic modulation of performance in response inhibition and interference control tasks.

Background: Inhibitory control is a crucial executive function with high relevance to mental and physical well-being. However, there are still unanswered questions regarding its neural mechanisms, including the role of the major inhibitory neurotransmitter, γ-aminobutyric acid (GABA).
Aims: This study examined the effects of lorazepam (0.5 mg and 1 mg), a positive allosteric modulator at the GABA _A receptor, on response inhibition and interference control. We also explored the heterogeneity of inhibitory control and calculated delta plots to explore whether lorazepam affects the gradual build-up of inhibition and activation over time.
Methods: N  = 50 healthy participants performed antisaccade, Eriksen flanker and Simon tasks in a within-subjects, placebo-controlled, double-blind randomized design.
Results: Lorazepam increased reaction time (RT) and error rates dose dependently in all tasks ( p  ⩽ 0.005). In the antisaccade and Simon tasks, lorazepam increased congruency effects for error rate ( p  ⩽ 0.029) but not RT ( p  ⩾ 0.587). In the Eriksen flanker task, both congruency effects were increased by the drug ( p  ⩽ 0.031). Delta plots did not reflect drug-induced changes in inhibition and activation over time. Delta plots for RT in the Simon task were negative-going, as expected, whereas those for the antisaccade and flanker tasks were positive-going.
Conclusions: This study provides evidence for GABAergic involvement in performance on response inhibition and interference control tasks. Furthermore, our findings highlight the diversity of the broader construct of inhibitory control while also pointing out similarities between different inhibitory control tasks. In contrast to RT and error rates, the cognitive processes indexed by delta plots may not be sensitive to GABAergic modulation.