The goal of this clinical trial is to learn about the effects of phase-targeted auditory stimulation in depressed patients and healthy controls.

The main questions it aims to answer are:

• Is auditory down-phase stimulation efficient in improving depression symptoms as compared to sham stimulation?
• Can mood and other outcomes be prospectively estimated by multi-parametric passive data?

Participants will perform auditory stimulation using a wearable device at home and provide data on their phone usage and activity.

Researchers will compare depressed patients and healthy participants to see if auditory down-phase stimulation effects them differently.

This study consists of two parts:

CLINICAL TRIAL PART: This part will be conducted in depressed and age- and sex-matched healthy participants. It has a double-blind, randomized crossover design. Each participant will undergo 1 week of baseline monitoring, followed by 1 week of in-home stimulation and 1 week of placebo condition interleaved with 1 week wash-out period. The last night of each intervention week will take place in a laboratory setting. A final week of follow-up will follow the second intervention week.

The following data is collected:

• Single-channel EEG (at home) and high-density electroencephalogram (hdEEG) (in laboratory)
• MR imaging
• Daily questionnaires
• Passive behavioural and physiological measurements

MONITORING PART: This observational study part will be conducted in depressed participants only. Each participant will undergo 5 weeks of remote monitoring using wearable devices and smartphones. Patients not eligible for the CLINICAL TRIAL PART, or that meet an exclusion criterion at any point in the study, can be assigned to this study part.

Inclusion Criteria:

• Male and female adults aged 18-55 years
• Motivated, no aversion against technology
• Able to give informed consent as documented by signature, and to follow the technical instructions
• Able to understand and speak German or English as required for the interview (HDRS) and to answer the questionnaires
• Diagnosis of depression according to DSM-5 criteria (depressed) OR no diagnosis of depression AND no depressive episode in the history (healthy)
• ≥17 points in Hamilton Depression Rating Score (HDRS, corresponding to at least moderate-mild depression, depressed) OR <8 points in HDRS (healthy)
• Stable or no pharmacological antidepressant therapy, no acute suicidal tendency (depressed)

Exclusion Criteria:

• Pregnant or lactating women, women planning to get pregnant during the study period
• Bipolar disorder or psychotic symptoms in the history
• Relevant disease or medication that could present a risk for the participant or that could influence study findings
• Known sleep apnea (diagnosed or ESS ≥10 points) or periodic limb movement syndrome
• Known alcoholism or drug abuse
• Diagnosed hearing impairment/presbycusis
• Irregular intake of centrally depressing or stimulating medication known to alter sleep EEG (e.g., benzodiazepines)
• History of traumatic brain injury (except for concussion) or neurosurgical procedures/operations
• Known epilepsy or for any reason, intracranial space-occupying lesions or (infectious or autoimmune) inflammatory diseases of the central nervous system
• Shift workers
• Inability to follow the procedures of the study, e.g., due to language problems, dementia, etc.
• Skin diseases/skin problems (in the face/ear/chest area) or allergies that could be aggravated by electrode application
• Conditions that may interfere with the MRI (e.g., MR unsafe cardiac pacemaker or a defibrillator, MR unsafe metal in or near the head, spinal cord, eyes, or in the chest)
• Indications of sleep apnea (Apnea Hypopnea Index >15/h) or periodic limb movement syndrome (PLMS index >15/h) in the screening night
• Low stimulation efficiency (<500 stimulations detected by the device) in the screening night or in 3 subsequent home recording nights, e.g., due to very little deep sleep
• Participation in another clinical trial during the study period

Data obtained through this study may be provided to qualified researchers with academic interest in sleep research and depression. Data or samples shared will be coded, with no PHI included. Approval of the request and execution of all applicable agreements (i.e. a material transfer agreement) are prerequisites to the sharing of data with the requesting party.

Data requests can be submitted starting after article publication

Access to trial IPD can be requested by qualified researchers engaging in independent scientific research, and will be provided following review and approval of a research proposal and execution of a Data Sharing Agreement (DSA)