Alterations to global but not local motion processing in long-term ecstasy (MDMA) users.
BACKGROUND
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.


OBJECTIVE
The aim of the present research was to investigate whether serotonin-mediated V1 visual processing deficits in ecstasy users extend to motion processing mechanisms.


METHODS
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 V5/MT.


RESULTS
"Primary" ecstasy users (n = 18), those without substantial polydrug use, had significantly lower global motion thresholds than controls [p = 0.027, Cohen's d = 0.78 (large)], indicating increased sensitivity to global motion stimuli, but no difference in local motion processing (p = 0.365).


CONCLUSIONS
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 V5/MT processing is reducing spatial suppression and therefore improving global motion perception in ecstasy users.
Research School of Psychology, The Australian National University, Building 39, Canberra, ACT, 0200, Australia, Claire.white@anu.edu.au.
Claire
C
White
John
J
Brown
Mark
M
Edwards
D000293:Adolescent; D000328:Adult; D004192:Discrimination, Psychological / Q000187:drug effects; D005260:Female; D006213:Hallucinogens / Q000494:pharmacology*; D006801:Humans; D008297:Male; D009039:Motion Perception / Q000187:drug effects*; D018817:N-Methyl-3,4-methylenedioxyamphetamine / Q000494:pharmacology*; D009778:Occipital Lobe / Q000187:drug effects / Q000378:metabolism; D011597:Psychomotor Performance / Q000187:drug effects*; D012701:Serotonin / Q000378:metabolism; D014796:Visual Perception / Q000187:drug effects; D055815:Young Adult; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D006213:Hallucinogens; D012701:Serotonin; D005680:gamma-Aminobutyric Acid; D018817:N-Methyl-3,4-methylenedioxyamphetamine