Two behavioral components related to impulsivity had opposite associations with subjective amphetamine response. More attention lapses predicted less response, while slower stopping predicted greater response in the same analysis.
Weafer and de Wit analyzed 165 healthy adults with usable task data after exclusions. Participants received placebo and 5, 10 and 20 mg d-amphetamine. Attention lapses were measured with a simple reaction-time task; impulsive action was indexed by stop-signal reaction time.
The component measures were assessed under placebo. They are not interchangeable with questionnaire impulsivity, ADHD diagnosis or a measured drug concentration. Subjective responses were evaluated with drug-effect and mood ratings.
At 20 mg, more lapses predicted lower ratings of liking, feeling the drug and wanting more. Longer stop-signal reaction time predicted greater ratings on those measures. Associations were also reported at 10 mg, while the corresponding behavioral-component associations were not significant at 5 mg.
The two components were positively correlated with each other at baseline, yet had diverging associations with drug response. A broad label such as impulsivity would therefore conceal information relevant to the actual result.
Regression adjustment included demographics and placebo-session order, but could not remove every influence of task familiarity or expectancy. The sample was healthy and lacked a history of stimulant dependence, limiting extension to clinical populations.
Liking and wanting ratings do not establish later drug-taking behavior, addiction or cognitive benefit. Nor do these task–rating associations provide an individual impairment threshold. The useful finding is component- and dose-specific: the relationship depended on whether the researcher measured lapses of attention or the speed of cancelling an action.
Read our analysis of questionnaire components and laboratory reinforcement.
Inattention, impulsive action, and subjective response to d-amphetamine. doi:10.1016/j.drugalcdep.2013.05.021.