Methylphenidate effects on prefrontal functioning during attentional-capture and response inhibition.

BACKGROUND: Methylphenidate improves motor response inhibition, typically assessed with the stop-signal task. The exact underlying mechanism for this, however, remains unknown. In addition, recent studies highlight that stop signals can have a confounding attentional-capture effect because of their low frequency in the task. In the current study, we assessed the effects of methylphenidate on neural networks of inhibitory control and attentional-capture within the context of two inhibitory control tasks.

METHODS: The effects of methylphenidate (40 mg) were assessed using functional magnetic resonance imaging in 16 healthy volunteers in a within-subject, double-blind, placebo-controlled design.

RESULTS: Methylphenidate significantly reduced activation of different regions within the right inferior frontal gyrus/insula to infrequent stimuli associated with successful inhibition, failed inhibition, and attentional capture. These inferior frontal gyrus regions showed different interregional connections with inhibitory and attention networks. For failed inhibitions, methylphenidate increased activation within performance-monitoring regions, including the superior frontal, anterior cingulate, and parietal-occipital cortices, but only after controlling for attentional capture.

CONCLUSIONS: Our findings suggest that the improvement of response inhibition seen following methylphenidate administration is due to its influence on underlying attentional mechanisms linked to response control requirements.