Mind After Midnight

Suicide risk is elevated during the biological night, particularly between 2:00 and 4:00 AM. Observational and epidemiologic data suggest that nocturnal wakefulness is associated with increased negative affect, impaired decision-making, and greater suicidal ideation. The "Mind After Midnight" hypothesis proposes that wakefulness during the biological night exposes individuals to a combination of circadian vulnerability and homeostatic sleep pressure that contributes to emotional and cognitive dysregulation.

This study will recruit approximately 90 adults with a history of suicidal ideation in the past six months. Participants will complete both home-based and laboratory-based procedures. Laboratory assessments will evaluate mood, hopelessness, suicidal ideation, impulsivity, and decision-making at different times of day, including 2:00-4:00 AM. To examine the role of homeostatic sleep pressure, participants will complete late-night assessments under two conditions: (1) high sleep pressure (remaining awake until 2:00 AM) and (2) low sleep pressure (sleeping and being awakened at 2:00 AM). Circadian factors will be assessed using behavioral measures and physiologic markers, including melatonin.

The goal of the study is to experimentally test whether nocturnal wakefulness contributes to suicide-associated cognitive and affective processes and to identify underlying chronobiological mechanisms.

Inclusion criteria

• Age 18-55 years
• History of suicidal ideation within the past 6 months
• Habitual bedtime between 9:00 PM and 1:00 AM
• Habitual wake time between 6:00 AM and 9:00 AM
• Ability to provide informed consent

Exclusion criteria

• Current suicidal intent requiring immediate clinical intervention
• Diagnosis of a primary sleep disorder (e.g., untreated obstructive sleep apnea, narcolepsy)
• Bipolar disorder or psychotic disorder
• Substance use disorder within the past 3 months
• Use of medications that significantly affect sleep or circadian rhythms
• Night shift work or transmeridian travel within the past month
• Medical or neurological condition that would interfere with participation
• Pregnancy