title: Chronic use of cannabis and poor neural efficiency in verbal memory ability.
abstract: BACKGROUND
  The endogenous cannabinoid system is sensitive to the introduction of exogenous cannabinoids such as delta-9-tetrahydrocannabinol, which are known to impact upon memory functioning. We sought to examine the impact of chronic cannabis use upon memory-related brain function via examination of the subsequent memory effect (SME) of the event-related potential (ERP).
  
  
  METHODS
  The SME is predictive of recall outcome and originates in structures that are dense with cannabinoid receptors (hippocampus and parahippocampus). The SME and performance on a verbal memory task were compared between 24 cannabis users (mean 17 years of near daily use) in the unintoxicated state and 24 non-using controls. The task involved the presentation of word lists, each with a short delay before recall. ERPs were recorded during encoding and later averaged by outcome (correctly recalled/not recalled).
  
  
  RESULTS
  Cannabis users showed poorer recall and altered patterns of SME activation: specifically, attenuation of the negative N4 and an increase in the late positive component. Duration of cannabis use and age of initial use correlated significantly with SME amplitudes. A longer history of use also correlated with greater recall that was related to N4 expression.
  
  
  CONCLUSIONS
  The results indicate that relative to non-using controls, chronic users of cannabis have altered memory-related brain activation in the form of dysfunctional SME production and/or poorer neural efficiency, which is associated with deficits in memory recall. Greater alteration was associated with a longer history of cannabis use and an earlier onset of use. Neuroadaptation to the effects of chronic exposure may additionally play a role.
authors.affiliation: School of Psychology, University of Wollongong, Wollongong, Australia. robert.battisti@sydney.edu.au
authors.forename: Robert A
authors.initials: RA
authors.lastname: Battisti
authors.forename: Steven
authors.initials: S
authors.lastname: Roodenrys
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Johnstone
authors.forename: Colleen
authors.initials: C
authors.lastname: Respondek
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Hermens
authors.forename: Nadia
authors.initials: N
authors.lastname: Solowij
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D004569:Electroencephalography; D005071:Evoked Potentials; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000503:physiopathology / Q000523:psychology*; D011939:Mental Recall / Q000187:drug effects*; D008875:Middle Aged; D009434:Neural Pathways / Q000187:drug effects* / Q000503:physiopathology; D009483:Neuropsychological Tests; D011930:Reaction Time; D013997:Time Factors; D014705:Verbal Behavior / Q000187:drug effects*; D055815:Young Adult