title: Semantic priming after ketamine acutely in healthy volunteers and following chronic self-administration in substance users.
abstract: BACKGROUND
  Ketamine is used acutely as a model of schizophrenia. It has been suggested that chronic ketamine may also mimic aspects of this disorder, in particular impaired cognitive function. As semantic processing deficits are considered central to cognitive impairments in schizophrenia, this study aimed to characterize semantic impairments following both acute and chronic ketamine.
  
  
  METHODS
  We examined the acute effects of two doses of ketamine (Experiment 1) using a double-blind, placebo-controlled, independent group design with 48 volunteers. Ketamine's chronic effects (Experiment 2) were explored in 16 ketamine users and 16 poly-drug controls. A semantic priming task with a frequency (high and low) and stimulus onset asynchrony (SOA: short-200 msec, long-750 msec) manipulation was used.
  
  
  RESULTS
  In Experiment 1, acute ketamine produced inverse priming at the long SOA. In Experiment 2, ketamine users showed inverse priming for low-frequency words at the long SOA compared to poly-drug controls.
  
  
  CONCLUSIONS
  The inverse priming effect at the long SOA induced by acute ketamine was indicative of controlled processing impairments. In ketamine users, there was also an indication of controlled processing impairments. Decreased priming for low-frequency words suggested that long-term ketamine abuse results in damage to the semantic store.
authors.affiliation: Clinical Psychopharmacology Unit, University College London, London WC1E 6BT, United Kingdom. c.morgan@ucl.ac.uk
authors.forename: Celia J A
authors.initials: CJ
authors.lastname: Morgan
authors.forename: Susan L
authors.initials: SL
authors.lastname: Rossell
authors.forename: Fiona
authors.initials: F
authors.lastname: Pepper
authors.forename: James
authors.initials: J
authors.lastname: Smart
authors.forename: James
authors.initials: J
authors.lastname: Blackburn
authors.forename: Brigitta
authors.initials: B
authors.lastname: Brandner
authors.forename: H Valerie
authors.initials: HV
authors.lastname: Curran
mesh_terms: D000328:Adult; D003072:Cognition Disorders / Q000139:chemically induced / Q000175:diagnosis; D004213:Dissociative Disorders / Q000139:chemically induced / Q000175:diagnosis; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D013287:Illicit Drugs / Q000494:pharmacology*; D007262:Infusions, Intravenous; D007649:Ketamine / Q000494:pharmacology*; D008297:Male; D009483:Neuropsychological Tests; D010153:Paired-Associate Learning / Q000187:drug effects*; D012559:Schizophrenia / Q000139:chemically induced* / Q000175:diagnosis; D012565:Schizophrenic Psychology; D019966:Substance-Related Disorders / Q000523:psychology*
chemical_list: D013287:Illicit Drugs; D007649:Ketamine