THINC-it Vortioxetine - Sensitivity to Change

MDD Population Inclusion Criteria: 1. The participant is able and willing to provide informed consent. 2. The participant is male or female 18-65 years of age. 3. The participant has received a current diagnosis of a major depressive episode (MDE) as part of MDD as per DSM-5 criteria. 4. The participant's current MDE is confirmed by the Mini International Neuropsychiatric Interview (M.I.N.I 5.0.). 5. The participant is an outpatient of a psychiatric setting. 6. The participant has a MADRS score ≥ 26 at screening and baseline. 7. The participant's reported duration of the current MDE is at least 3 months. 8. At least one prior major depressive episode validated by previous treatment (e.g., guideline-informed pharmacotherapy and/or manual-based psychotherapy). 9. All participants will be screened for cognitive impairment based on DSST performance (pen-and-paper version) with a maximum baseline score of 70 correct symbols entered to avoid ceiling effects. Exclusion Criteria: 1. Current alcohol and/or substance use disorder. 2. Presence of comorbid psychiatric disorder other than MDD that is a focus of clinical concern as confirmed by the M.I.N.I 5.0. 3. Medications approved and/or employed off-label for cognitive dysfunction (e.g., psychostimulants). 4. Any medication for a general medical disorder that, in the opinion of the investigator, may affect cognitive function (e.g., corticosteroids, beta-blockers). 5. Use of benzodiazepines within 12 hours of cognitive assessments. 6. Consumption of alcohol within 8 hours of cognitive assessments. 7. Recent use of marijuana as determined by a toxicology screen. 8. Physical, cognitive, or language impairments sufficient to adversely affect data derived from cognitive assessments. 9. Diagnosis reading disability or dyslexia. 10. Clinically significant learning disorder by history. 11. Electroconvulsive therapy (ECT) in the last 6 months. 12. History of moderate or severe head trauma (e.g., loss of consciousness for \>1 hour), other neurological disorders, or unstable systemic medical diseases that in the opinion of the investigator are likely to affect the central nervous system. 13. Pregnant and/or breastfeeding. 14. Received investigational agents as part of a separate study within 30 days of the screening visit. 15. Actively suicidal or evaluated as being a suicide risk (a score of \> 4 on the MADRS and/or per clinical judgment using the Columbia-Suicide Severity Rating Scale). 16. Currently receiving treatment with Monoamine Oxidase Inhibitors (MAOIs) anti-depressants, antibiotics such as linezolid, or intravenous methylene blue. Healthy Control Population Inclusion Criteria: 1. No current or past history of mental disorder as evidenced by the M.I.N.I. 5.0 for DSM-IV. 2. No first-degree relative with an established diagnosis by a healthcare provider of a mood or psychiatric disorder. 3. No unstable medical disorders. Exclusion Criteria: 1. Use of any medication for a general medical disorder and/or condition that, in the opinion of the investigator, may affect cognitive function (e.g., corticosteroids, beta-blockers). 2. Pregnant and/or breastfeeding. 3. Consumption of alcohol within 8 hours of THINC-it tool administration. 4. Recent use of marijuana as determined by a toxicology screen.