Attentional bias to incentive stimuli in frequent ketamine users.

BACKGROUND: The attention-grabbing properties of drugs to drug-using individuals have been well documented and recent research has begun to suggest that such attentional bias may be related to the severity of drug dependency. Dependence on ketamine has been reported anecdotally but no systematic study has investigated this phenomenon. We aimed to explore attentional biases to incentive stimuli in different populations of ketamine users.
METHOD: Using a dot-probe paradigm, attentional bias to both drug-related and money-related stimuli was investigated in 150 participants: 30 frequent ketamine users, 30 infrequent ketamine users, 30 ex-ketamine users, 30 poly-drug users and 30 non-drug-using controls. Two stimulus presentation times were used (200 and 2000 ms) to investigate whether attentional bias was as a result of an automatic or a more conscious attentional shift. Participants also rated the degree to which stimuli used in the dot-probe paradigm were pleasurable.
RESULTS: Frequent ketamine users demonstrated an attentional bias to both types of incentive stimuli only at the short stimulus presentation interval and this was significantly correlated with degree of ketamine use. No attentional biases were observed in any of the other groups. All groups rated money stimuli as more pleasurable than neutral stimuli.
CONCLUSIONS: These data support incentive models of drug use and demonstrate the ability of the attentional bias paradigm to discriminate recreational drug users from those with more dependent patterns of use. Ketamine is a potentially dependence-forming drug.