Inclusion Criteria:

• Patients with mild or moderate TBI will be included. To be included, a subject must meet the criteria below:
• 1. Non-penetrating mild or moderate traumatic brain injury that occurred 3 or more months prior to study entry (to minimize natural recovery from TBI)
• 2. Age: 18-64 years
• 3. Meeting any one of the following severity criteria, as documented in the patient's medical records:
• 1. Glasgow Coma Scale (GCS) score of 9-15 within 4 hours after injury
• 2. Loss of consciousness (LOC) \>1 minute and \<=24 hours
• 3. Post-traumatic amnesia (PTA) \< 7 days
• 4. English-speaking
• 5. Current DSM-5 diagnosis of Major Depressive Episode by medical record diagnosis
• 6. HAM-D-21 score of 18 or higher
• 7. Patients who are considered to be appropriate by their clinician and who are willing to be started on Buspirone and Melatonin for clinical purposes.

Exclusion Criteria:

• 1. History of neurological disorder (e.g., stroke, epilepsy, multiple sclerosis, HIV, neurodegenerative disorders) or any acute or unstable medical condition that is likely to interfere with the assessments or with participation in treatment, as determined by history by the patient or review of their medical records.
• 2. Evidence from the history of TBI severity greater than moderate, i.e., GCS of 8 or less, LOC \> 24 hours, or PTA \> 7 days.
• 3. Inability to attend regular appointments
• 4. Imminent risk of suicide, as determined by the assessing clinician; HAM-D, Question 3, answers \> 1; SDQ, Question 11, answers \> 3; spontaneous expressions of suicidal ideation will result in emergency evaluation by a licensed clinician member of study staff for appropriate assessment and triage.
• 5. Lifetime history of schizophrenia or other primary psychotic disorders, as determined by history by the patient or review of their medical records.
• 6. History of bipolar disorder, as determined by history by the patient or review of their medical records.
• 7. Alcohol or substance dependence in the past 3 months, as determined by history by the patient or review of their medical records.
• 8. Pregnancy or breast-feeding
• 9. Concomitant use of buspirone, any psychostimulant, or modafinil/armodafinil
• 10. Patients currently on an antidepressant or who have been on antidepressant in the past 4 weeks
• 11. Patients with prior intolerances to buspirone or melatonin.
• 12. Conditions that would preclude a subject from participating in the MRI procedures (e.g., metal implants, aneurysm clips, shrapnel/retained particles, pacemakers, claustrophobia).