Alterations to global but not local motion processing in long-term ecstasy (MDMA) users.
Growing evidence indicates that the main psychoactive ingredient in the illegal drug ecstasy (methylendioxymethamphetamine) causes reduced activity in the serotonin and gamma-aminobutyric acid (GABA) systems in humans. On the basis of substantial serotonin input to the occipital lobe, recent research investigated visual processing in long-term users and found a larger magnitude of the tilt aftereffect, interpreted to reflect broadened orientation tuning bandwidths. Further research found higher orientation discrimination thresholds and reduced long-range interactions in the primary visual area of ecstasy users. The aim of the present research was to investigate whether serotonin-mediated V1 visual processing deficits in ecstasy users extend to motion processing mechanisms. Forty-five participants (21 controls, 24 drug users) completed two psychophysical studies A direction discrimination study directly measured local motion processing in V1, while a motion coherence task tested global motion processing in area V5MT. Primary ecstasy users (n 18), those without substantial polydrug use, had significantly lower global motion thresholds than controls p 0.027, Cohens d 0.78 (large), indicating increased sensitivity to global motion stimuli, but no difference in local motion processing (p 0.365). These results extend on previous research investigating the long-term effects of illicit drugs on visual processing. Two possible explanations are explored defuse attentional processes may be facilitating spatial pooling of motion signals in users. Alternatively, it may be that a GABA-mediated disruption to V5MT processing is reducing spatial suppression and therefore improving global motion perception in ecstasy users.