This trial attempts to investigate whether 10 sessions of tACS improves cognitive function, especially which domains of cognitive function are most improved and to investigate whether 10 sessions of tACS affecting brain activation during a working memory task and changes patterns of brain connectivity networks.Subjects will be divided into 2 groups 2:1, active and sham tACS. 50 subjects will be in the active group, and 25 subjects in the sham group (specific numbers to be decided on later).

Schizophrenia patients (SZ) show profound and persistent cognitive deficits in attention, executive processing, and verbal and visuospatial memory, which persist even after psychotic symptoms are ameliorated. Cognitive deficits may be more important in preventing functional, occupational, and social recovery in SZ than other symptom domains and are not effectively treated by current pharmacological approaches. Alternating current stimulation (tACS) is less expensive than other modalities (e.g. repetitive transcranial magnetic stimulation; rTMS), easily available, and has a good safety profile in healthy controls (HC) and SZ. The ability to entrain γ oscillations with 40Hz tACS, might compensate more specifically for this deficit in γ oscillations in schizophrenia, and, may therefore, produce more robust behavioral improvements in working memory and other aspects of cognition.However, no studies have looked at the effects of multiple daily tACS stimulation at a 40HZ γ frequency on cognitive function and symptoms in schizophrenia. This provides a rationale for the current study, which proposes to investigate the effects of 10 sessions of 40HZ tACS on cognitive functions, symptoms in schizophrenia.

Active vs. sham treatment will be randomly assigned in a 2:1 fashion (A:S) in groups using computer generated lists. Subjects and tDCS testers or evaluators will be blind to treatment. Subjects will be evaluated with cognitive, symptom and functional measures at baseline, within 1 day ( or 2 days fro some measures) after 10 sessions, 2 weeks after 10 sessions, 1 month after 10 sessions, and 2 months after 10 sessions.After the 1 month evaluation, subjects in the initial active tACS group will be randomly assigned to receive either 5 booster sessions of either active or sham tACS ( 25 subjects each), following parameters used in the initial treatment. Subjects in the initial Sham group will receive 5 booster session Sham tACS. Participants will be scanned once prior to tACS sessions, and within 3 days after the 10th tACS session, using our Siemens 3T Tim Verio MRI scanner with a standard 32-channel phased-array head coil.

Inclusion Criteria:

• Subjects who have cognitive deficits as indicated by a score of < 85 on RBANS, and meet criteria for DSM-5 diagnosis of chronic SZ, schizoaffective disorder (SA), or schizophreniform disorder (SZF), and who are stably treated with antipsychotic medications and are not in acute exacerbation of illness symptoms.

Exclusion Criteria:

• Patients with risk factors for an MRI scan, seizure disorder, and for women of childbearing age who are pregnant or regularly engaging in sexual activity and not regularly using an acceptable birth control method (systemic or double-barrier).