Circadian downshift failure explains insomnia

A 24‑hour circadian isolation study found that older adults with chronic insomnia do not shift their cognitive state from daytime problem‑solving to nighttime disengagement as strongly as good sleepers. The deficit appears intrinsic to the brain’s transition mechanisms (not just environment or behavior) and was measured hourly in a dim, time‑neutral setting. — If insomnia reflects a failure to disengage biologically, public health and clinical strategies should prioritize disorder‑specific circadian and neural interventions rather than one‑size‑fits‑all sleep hygiene advice.