Inclusion Criteria:
1. Age19-55 years old, inclusive
2. Sufficient fluency in English to understand testing procedures and provide informed consent
3. In one of these three diagnostic groups:
1. Schizophrenia Spectrum Disorder (SSD), which can include the diagnoses of Schizophrenia, Schizoaffective Disorder, Unspecified Schizophrenia Spectrum, Schizophreniform Disorder, Brief Psychotic Episode, or Psychotic Disorder NOS (as defined by DSM-V and determined by the Mini International Neuropsychiatric Interview (MINI)
2. Unipolar Major Depressive Disorder (MDD) of any subtype. Depressed participants will have a score of \>18 on the Montgomery Asberg Depression Rating Scale (MADRS), as defined by DSM-V and determined by the Mini International Neuropsychiatric Interview (MINI)
3. Normal healthy controls, individuals with no personal history of any Axis I disorder. Controls will have a MADRS score of \<7.
Exclusion Criteria:
1. Reported pregnancy and/or nursing. A participant may only take part if they are sexually abstinent or using a reliable method of birth control (birth control pills, Norplant, condoms and spermicide).
2. Evidence of alcohol or other substance use disorder in the past 3 months
3. Diagnosis of other primary psychiatric disorder (defined in this case as being the main focus of treatment) as determined by the MINI, such as: bipolar disorder, personality disorders, post-traumatic stress disorder, obsessive-compulsive disorder, dissociative disorders, eating disorder, or cognitive deficits due to neurological conditions
4. Imminent suicide or homicide risk as determined by the investigator
5. Being treated with one of the following medications: benzodiazepines or other CNS depressants.
6. No clinically significant neurological disease based on medical history (e.g., epilepsy) or significant head injury.
7. Any of the following disorders are exclusionary: Rheumatoid arthritis; Lupus erythematosus; Autoimmune hepatitis; Autoimmune peripheral neuropathy; Autoimmune pancreatitis; Behcet's disease; Crohn's disease; Autoimmune glomerulonephritis; Grave's disease; Guillain-Barre syndrome; Hashimoto's thyroiditis; Autoimmune polymyositis or polymyalgia; Myasthenia gravis; Narcolepsy; Polyarteritis nodosa; Scleroderma; Sjogren's syndrome; Transverse myelitis; Wegener's granulomatosis; History of seizures (only childhood febrile seizures are allowed)
8. Patients with prior exposure to VNS therapy whether using an implantable or external device
9. An active implantable medical device, such as a pacemaker, hearing aid implant, or any implanted electronic device
10. A metallic device, such as a stent, bone plate, or bone screw, implanted at or near the neck
11. An open wound, rash, infection, swelling, cut, sore, drug patch, or surgical scar(s) on the neck at the treatment location
12. Patients diagnosed with narrowing of the arteries (carotid atherosclerosis)
13. Patients who have had surgery to cut the vagus nerve in the neck (cervical vagotomy)
14. Exclusion criteria for control subjects include any history of mental illness or psychotropic drug abuse.
