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


OBJECTIVE
This study compared the effects of diazepam with methylphenidate on fear conditioning.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Brignell
Catherine M
CM
School of Psychology, University of Southampton, Highfield, Southampton, SO17 1BJ, UK. c.brignell@soton.ac.uk
Curran
H Valerie
HV
D000328:Adult; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003214:Conditioning, Classical / Q000187:drug effects*; D003975:Diazepam / Q000494:pharmacology*; D004644:Emotions; D005108:Extinction, Psychological / Q000187:drug effects; D005239:Fear; D005712:Galvanic Skin Response / Q000187:drug effects; D006185:Habituation, Psychophysiologic / Q000187:drug effects; D006801:Humans; D008568:Memory / Q000187:drug effects; D008774:Methylphenidate / Q000494:pharmacology*; D009622:Noise; D010775:Photic Stimulation; D012016:Reference Values; D012054:Reinforcement, Psychology; D012107:Research Design; D013546:Sweating / Q000187:drug effects*
D014151:Anti-Anxiety Agents; D000697:Central Nervous System Stimulants; D008774:Methylphenidate; D003975:Diazepam