title: Differential effects of cannabis dependence on cortical inhibition in patients with schizophrenia and non-psychiatric controls.
abstract: Cannabis is the most commonly used illicit substance among patients with schizophrenia. Cannabis exacerbates psychotic symptoms and leads to poor functional outcomes. Dysfunctional cortical inhibition has been implicated in the pathophysiology of schizophrenia; however, the effects of cannabis on this mechanism have been relatively unexamined. The goal of this study was to index cortical inhibition from the motor cortex among 4 groups: schizophrenia patients and non-psychiatric controls dependent on cannabis as well as cannabis-free schizophrenia patients and non-psychiatric controls.
  
  
  
  In this cross-sectional study, GABA-mediated cortical inhibition was index with single- and paired-pulse transcranial magnetic stimulation (TMS) paradigms to the left motor cortex in 12 cannabis dependent and 11 cannabis-free schizophrenia patients, and in 10 cannabis dependent and 13 cannabis-free controls.
  
  
  
  Cannabis-dependent patients with schizophrenia displayed greater short-interval cortical inhibition (SICI) compared to cannabis-free schizophrenia patients (p = 0.029), while cannabis-dependent controls displayed reduced SICI compared to cannabis-free controls (p = 0.004). SICI did not differ between cannabis dependent patients and cannabis-free controls, or between dependent schizophrenia patients compared to dependent controls. No significant differences were found for long-interval cortical inhibition (LICI) or intra-cortical facilitation (ICF) receptor function, suggesting a selective effect on SICI.
  
  
  
  These findings suggest that cannabis dependence may have selective and differing effects on SICI in schizophrenia patients compared to controls, which may provide insight into the pathophysiology of co-morbid cannabis dependence in schizophrenia.
authors.affiliation: Schizophrenia Division, Centre for Addiction and Mental Health (CAMH), 250 College Street, Toronto M5T 1R8, ON, Canada; Temerty Centre for Therapeutic Brain Intervention, CAMH, 1001 Queen Street West, Toronto M6J 1H4 ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, 1 King's College Circle Room 2374, Toronto M5S 1A8, ON, Canada.
authors.forename: Michelle S
authors.initials: MS
authors.lastname: Goodman
authors.affiliation: Schizophrenia Division, Centre for Addiction and Mental Health (CAMH), 250 College Street, Toronto M5T 1R8, ON, Canada; Temerty Centre for Therapeutic Brain Intervention, CAMH, 1001 Queen Street West, Toronto M6J 1H4 ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, 1 King's College Circle Room 2374, Toronto M5S 1A8, ON, Canada.
authors.forename: Alanna C
authors.initials: AC
authors.lastname: Bridgman
authors.affiliation: Schizophrenia Division, Centre for Addiction and Mental Health (CAMH), 250 College Street, Toronto M5T 1R8, ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, 1 King's College Circle Room 2374, Toronto M5S 1A8, ON, Canada.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Rabin
authors.affiliation: Division of Brain and Therapeutics, Department of Psychiatry, University of Toronto, 250 College Street, Toronto M5T 1R8, ON, Canada; Temerty Centre for Therapeutic Brain Intervention, CAMH, 1001 Queen Street West, Toronto M6J 1H4 ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, 1 King's College Circle Room 2374, Toronto M5S 1A8, ON, Canada; Division of Geriatric Psychiatry, CAMH and Department of Psychiatry, University of Toronto, 80 Workman Way, Toronto M6J 1H4, ON, Canada.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Blumberger
authors.affiliation: Division of Brain and Therapeutics, Department of Psychiatry, University of Toronto, 250 College Street, Toronto M5T 1R8, ON, Canada; Temerty Centre for Therapeutic Brain Intervention, CAMH, 1001 Queen Street West, Toronto M6J 1H4 ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, 1 King's College Circle Room 2374, Toronto M5S 1A8, ON, Canada; Division of Geriatric Psychiatry, CAMH and Department of Psychiatry, University of Toronto, 80 Workman Way, Toronto M6J 1H4, ON, Canada.
authors.forename: Tarek K
authors.initials: TK
authors.lastname: Rajji
authors.affiliation: Division of Brain and Therapeutics, Department of Psychiatry, University of Toronto, 250 College Street, Toronto M5T 1R8, ON, Canada; Temerty Centre for Therapeutic Brain Intervention, CAMH, 1001 Queen Street West, Toronto M6J 1H4 ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, 1 King's College Circle Room 2374, Toronto M5S 1A8, ON, Canada.
authors.forename: Zafiris J
authors.initials: ZJ
authors.lastname: Daskalakis
authors.affiliation: Schizophrenia Division, Centre for Addiction and Mental Health (CAMH), 250 College Street, Toronto M5T 1R8, ON, Canada; Division of Brain and Therapeutics, Department of Psychiatry, University of Toronto, 250 College Street, Toronto M5T 1R8, ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, 1 King's College Circle Room 2374, Toronto M5S 1A8, ON, Canada.
authors.forename: Tony P
authors.initials: TP
authors.lastname: George
authors.affiliation: Schizophrenia Division, Centre for Addiction and Mental Health (CAMH), 250 College Street, Toronto M5T 1R8, ON, Canada; Division of Brain and Therapeutics, Department of Psychiatry, University of Toronto, 250 College Street, Toronto M5T 1R8, ON, Canada; Temerty Centre for Therapeutic Brain Intervention, CAMH, 1001 Queen Street West, Toronto M6J 1H4 ON, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, 1 King's College Circle Room 2374, Toronto M5S 1A8, ON, Canada. Electronic address: mera.barr@camh.ca.
authors.forename: Mera S
authors.initials: MS
authors.lastname: Barr
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000503:physiopathology* / Q000628:therapy*; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D011618:Psychotic Disorders / Q000503:physiopathology / Q000628:therapy; D012559:Schizophrenia / Q000503:physiopathology* / Q000628:therapy*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Cannabis; Cortical inhibition; GABA; Schizophrenia; Transcranial magnetic stimulation