tDCS for Schizophrenia and Schizoaffective Disorder

Inclusion Criteria: Enrolment in the tDCS-adherence parent study (REB# 103-2018). The parent study inclusion criteria are: 1. Male or female participants of any race or ethnicity 2. Inpatients or outpatients ≥18 years of age 3. DSM-V diagnosis of schizophrenia or schizoaffective disorder 4. Capable of consenting to participate in the research study 5. On a stable dose of oral antipsychotic drug and other concomitant medications for at least 2 months, and unlikely to undergo changes in dose during the study. Exclusion Criteria: The exclusion criteria for this study will be the same as the parent study (REB 103-2018). The parent study exclusion criteria are: 1. Unwilling or incapable to consent to the study based on the MacArthur Test of Competence 2. Unstable medical or any concomitant major medical or neurological illness, including a history of seizures 3. Acute suicidal or homicidal ideation 4. Formal thought disorder rating ≥3 on the Positive and Negative Syndrome Scale (PANSS) P2 conceptual disorganization item 5. DSM-V substance dependence (except caffeine, nicotine, and cannabis/marijuana) within 1 month of entering the study 6. Positive urine drug screen except for cannabis/marijuana at the screening visit 7. Metal implants or pacemaker precluding an MRI scan or other contraindications to MRI (e.g., claustrophobia) 8. Pregnancy 9. Score \<32 on the Wide Range Achievement Test-III Additional exclusion criteria for this companion study are: 1. Unwilling or incapable to consent to the study based on the MacArthur Test of Competence 2. Exposure to long-acting injectable antipsychotics in the last 6 months 3. Exceeding allowed annual radiation exposure levels (20 mSv), as outlined by our PET Centre guidelines 4. Receiving treatment with medications such as levetiracetam that blocks SV2a binding 5. Disorders of coagulation or taking anticoagulant medication 6. Having completed multiple PET scans in the past, such that participation in this study would cause participant to exceed lifetime limit (8 PET scans)