Inclusion Criteria:

Unipolar Depression Cohort

Subjects must meet all of the following criteria for study participation:

1. Subject is age ≥18 years and ≤75 years.
2. Subject has current, moderate-to-severe depressive episode of the unipolar type, based on DSM-IV criteria for diagnosis as documented by clinician administered M.I.N.I. AND HAMD-17 score ≥17.
3. Patient is willing and clinically is appropriate to pursue treatment with selective serotonin reuptake inhibitor fluoxetine, paroxetine, sertraline, citalopram, or escitalopram. If on non SSRI antidepressant, would be willing to taper discontinue antidepressant and after 1 week, start treatment with above listed SSRI.
4. Subject is willing and able to provide consent.
5. Subject has ability to read and understand the instructions for the study.
6. Subject is willing to adhere to study procedures.

Bipolar Depression Cohort

Subjects must meet all of the following criteria for study participation:

1. Subject is age ≥18 years and ≤75 years.
2. Subject has current, moderate-to-severe depressive episode of the bipolar I or II type, based on DSM-IV criteria for diagnosis as documented by clinician administered M.I.N.I. AND HAMD-17 score ≥17.
3. Subject has not yet started therapy appropriate for bipolar depression (pharmacologic or otherwise).
4. Patient is willing and clinically is appropriate to pursue treatment with lithium, lamotrigine, or valproate for treatment of bipolar I or II depression.If on SSRI antidepressant, would be willing to taper discontinue antidepressant and after 1 week, start treatment with above listed mood stabilizer.
5. Subject is willing and able to provide consent.
6. Subject has ability to read and understand the instructions for the study.
7. Subject is willing to adhere to study procedures.

Control Cohort

Subjects must meet all of the following criteria for study participation:

1. Subject is age ≥18 years and ≤75 years.
2. Subject is willing and able to provide consent.
3. Subject has ability to read and understand the instructions for the study.
4. Subject is willing to adhere to study procedures.

Exclusion Criteria: 

Unipolar Depression Cohort

Subjects will be excluded from study participation if any of the following criteria are met:

1. Subject has presence of no or mild Major Depressive Disorder Episode, based on DSM-IV criteria for diagnosis as documented by clinician administered M.I.N.I OR HAMD-17 rating scale score <17.
2. Subject has bipolar disorder.
3. Subject has active psychotic symptoms.
4. Subject has known or is suspected to have a personality disorder that is the current driver of current symptoms
5. Subject has current suicidality of medium or high risk as determined by M.I.N.I. or HAMD-17 item #3 score of 3 of higher.
6. Subject has history of central or obstructive sleep apnea OR has a STOP-BANG score of ≥5[1] OR has a Home Sleep Test assessment (ApneaLink, ResMed) demonstrating AHI≥15.
7. Subject has a pacemaker.
8. Subject currently uses benzodiazepines, sedative-hypnotics, or trazadone on a scheduled basis OR will be likely be prescribed such medication during the 8-week observational phase of the study.
9. Subject currently uses antipsychotic medication for any indication OR will be likely be prescribed such medication during the 8-week observational phase of the study.
10. Subject currently uses chronotropic medication, such as beta-blockers, digoxin, sinoatrial/atrioventricular nodal-acting calcium channel blockers, and amiodarone.
11. Subject is suspected or known to have active alcohol or drug abuse (including but not limited to abuse of marijuana).
12. Subject has a terminal illness.
13. For female subjects, subject is currently known to be pregnant or lactating.
14. Subject has any other acute or chronic condition that in the investigators opinion would preclude the subject from being able to meet all of the protocol requirements, or would compromise the subject’s safety during participation in the study, as judged by the investigator.
15. Subject is currently participating in another clinical study, or participated in a clinical study in the past 30 days during which an investigational device or drug was used.
16. Subject will be starting additional new treatment (i.e ECT, TMS, psychotherapy) for depression during the study.

Bipolar Depression Cohort

Subjects will be excluded from study participation if any of the following criteria are met:

1. Subject has presence of no or mild Major Depressive Disorder Episode, based on DSM-IV criteria for diagnosis as documented by clinician administered M.I.N.I OR HAMD-17 rating scale score <17.
2. Subject has active psychotic symptoms.
3. Subject has known or is suspected to have a personality disorder.
4. Subject has current suicidality of medium or high risk as determined by M.I.N.I. or HAMD-17 item #3 score of 3 of higher.
5. Subject has history of central or obstructive sleep apnea OR has a STOP-BANG score of ≥5 OR has a Home Sleep Test assessment (ApneaLink, ResMed) demonstrating AHI≥15.
6. Subject has a pacemaker.
7. Subject currently uses benzodiazepines, sedative-hypnotics, or trazadone on a scheduled basis OR will be likely be prescribed such medication during the 8-week observational phase of the study.
8. Subject currently uses antipsychotic medication for any indication OR will be likely be prescribed such medication during the 8-week observational phase of the study.
9. Subject currently uses chronotropic medication, such as beta-blockers, digoxin, sinoatrial/atrioventricular nodal-acting calcium channel blockers, and amiodarone.
10. Subject is suspected or known to have active alcohol or drug abuse (including but not limited to abuse of marijuana).
11. Subject has a terminal illness.
12. For female subjects, subject is currently known to be pregnant or lactating.
13. Subject has any other acute or chronic condition that in the investigators opinion would preclude the subject from being able to meet all of the protocol requirements, or would compromise the subject’s safety during participation in the study, as judged by the investigator.
14. Subject is currently participating in another clinical study, or participated in a clinical study in the past 30 days during which an investigational device or drug was used.
15. Subject will be starting additional new treatment (i.e ECT, TMS, psychotherapy) for depression during the study.

Control Cohort

Subjects will be excluded from study participation if any of the following criteria are met:

1. Subject has presence of mild, moderate, or severe Major Depressive Disorder Episode, based on DSM-IV criteria for diagnosis as documented by clinician administered M.I.N.I OR HAMD-17 rating scale score >7.
2. Subject has bipolar disorder.
3. Subject has active psychotic symptoms.
4. Subject has known or is suspected to have a personality disorder.
5. Subject has current suicidality of medium or high risk as determined by M.I.N.I. or HAMD-17 item #3 score of 3 of higher.
6. Subject has history of central or obstructive sleep apnea OR has a STOP-BANG score of ≥5 OR has a Home Sleep Test assessment (ApneaLink, ResMed) demonstrating AHI≥15.
7. Subject has a pacemaker.
8. Subject currently uses benzodiazepines, sedative-hypnotics, or trazadone on a scheduled basis OR will be likely be prescribed such medication during the 8-week observational phase of the study.
9. Subject currently uses antipsychotic medication for any indication OR will be likely be prescribed such medication during the 8-week observational phase of the study.
10. Subject currently uses chronotropic medication, such as beta-blockers, digoxin, sinoatrial/atrioventricular nodal-acting calcium channel blockers, and amiodarone.
11. Subject is suspected or known to have active alcohol or drug abuse (including but not limited to abuse of marijuana).
12. Subject has a terminal illness.
13. For female subjects, subject is currently known to be pregnant or lactating.
14. Subject has any other acute or chronic condition that in the investigators opinion would preclude the subject from being able to meet all of the protocol requirements, or would compromise the subject’s safety during participation in the study, as judged by the investigator.
15. Subject is currently participating in another clinical study, or participated in a clinical study in the past 30 days during which an investigational device or drug was used.