Drugs, sweat, and fears: a comparison of the effects of diazepam and methylphenidate on fear conditioning

Classical conditioning of a fear response involves the formation of an association between a stimulus and an emotional response and can be seen as a basic form of emotional memory. While both benzodiazepines and stimulant drugs may influence the formation of episodic memories for emotional events, their effects on fear conditioning are less clear. This study compared the effects of diazepam with methylphenidate on fear conditioning. In a single-session between groups design with three conditions [placebo, diazepam (10 mg), and methylphenidate (40 mg)], classical conditioning of a skin conductance response to a visual stimulus previously paired with a 100-db white noise was tested in 45 healthy volunteers. Diazepam blocked fear conditioning, despite responses to the unconditioned aversive stimulus and neutral control stimulus being unimpaired. Conditioning remained intact after methylphenidate. Conditioned responses were not extinguished completely by the end of the experiment, and it was not possible to draw conclusions about the effects of the drugs on extinction. Although diazepam has well-documented amnesic effects, it has not been found to affect implicit forms of memory like perceptual and conceptual priming. As the present study found impaired fear conditioning after diazepam, it adds weight to recent findings that emotional memories are disproportionately impaired by the benzodiazepines.