The Mind After Midnight: Nocturnal Wakefulness and the ANSWERS Project

Abstract

Disrupted sleep is a risk factor for incident and worsening psychiatric disorders and suicide. However, sleep and wakefulness occur in the broader context of circadian rhythms, the neural patterning that synchronizes our physiology and behavior with the external rhythms of day and night. Although extensive research has connected disrupted sleep to next-day deficits in cognitive and emotional functioning, comparatively little effort has focused on what happens to the brain, and to behavior, during the biological night. In this manuscript, I present the Mind after Midnight, a conceptualization of neurophysiological and cognitive changes that occur during the circadian night and which have profound implications for dysregulated behavior and psychopathology, including suicide, violent crime, and substance abuse. First, I review the extant evidence for nocturnal changes in behavioral propensity by focusing on epidemiological and experimental evidence for suicide, suicidal thoughts and behaviors, homicide/violent crime, alcohol and substance use, and food intake. I subsequently examine the available evidence for sleep- and circadian-dependent nocturnal changes in synaptic/neurotransmitter systems, mood/affect, reward processing, and executive function, which I then into the hypothetical Mind after Midnight. Finally, I present the ongoing work of the Addressing Nocturnal Sleep/Wake Effects on Risk of Suicide (ANSWERS) Project to explore the Mind after Midnight using translational and clinical research.