Catecholamine modulation of evidence accumulation during perceptual decision formation; a randomised trial

Recent behavioural modelling and pupillometry studies suggest that neuromodulatory arousal systems play a role in regulating decision formation but neurophysiological support for these observations is lacking. We employed a randomised, double-blinded, placebo-controlled, crossover design to probe the impact of pharmacological enhancement of catecholamine levels on perceptual decision making. Catecholamine levels were manipulated using the clinically relevant drugs methylphenidate (MPH) and atomoxetine (ATM) and their effects were compared to those of citalopram (CIT), and placebo (PLA). Participants performed a classic EEG oddball paradigm which elicits the P3b, a centro-parietal potential that has been shown to trace evidence accumulation, under each of the four drug conditions. We found that MPH and ATM administration shortened RTs to the oddball targets. The neural basis of this behavioural effect was an earlier P3b peak latency, driven specifically by an increase in its build-up rate without any change in its time of onset or peak amplitude. This study provides neurophysiological evidence for the catecholaminergic enhancement of a discrete aspect of human decision making, i.e. evidence accumulation. Our results also support theoretical accounts suggesting that catecholamines may enhance cognition via increases in neural gain.