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

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Abstract

Rationale

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.

Objectives

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

Materials and 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.

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Notes

  1. i.e., on a trial were a participant gave no response, their response was counted as −2 log10 μS; i.e., trials with no recordable response were included in this calculation, but not the calculation of amplitude. Data available on request.

  2. Hamann et al. 2002 argue that because the response to the US is so much larger than the response to the CS+, the response to the CS+US combined can be used to accurately estimate response to the US.

  3. The covariate was not used in this analysis as all the participants made responses to the CS+US combination in the continuous reinforcement phase.

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Authors and Affiliations

  1. School of Psychology, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

    Catherine M. Brignell

  2. Clinical Psychopharmacology Unit, Sub-dept of Clinical Health Psychology, University College London, Gower Street, London, WC1H 6BT, UK

    H. Valerie Curran

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  1. Catherine M. Brignell
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  2. H. Valerie Curran
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Correspondence to Catherine M. Brignell.

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Brignell, C.M., Curran, H.V. Drugs, sweat, and fears: a comparison of the effects of diazepam and methylphenidate on fear conditioning. Psychopharmacology 186, 504–516 (2006). https://doi.org/10.1007/s00213-006-0363-x

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  • DOI: https://doi.org/10.1007/s00213-006-0363-x

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