When stress becomes wakefulness: Stress-arousal circuitry and the state control of insomnia.

Insomnia disorder (ID) is the most common sleep disorder and among the most prevalent neuropsychiatric conditions, affecting ∼9-20% of adults with substantial burden. Chronic ID is linked to cardiometabolic and psychiatric morbidity, cognitive impairment, and accelerated neurodegeneration. Although behavioral and pharmacologic therapies help, relapse is common, suggesting a pathophysiology not simply of "too little sleep" but a persistent bias toward wakefulness. Current models converge on ID as a disorder of hyperarousal, yet the circuit, cellular, and synaptic mechanisms by which stress produces a durable wake-biased state remain unclear. Here we synthesize clinical and mechanistic evidence that stress-responsive hubs, particularly the paraventricular nucleus of the hypothalamus (PVN) and bed nucleus of the stria terminalis (BNST), interact with hypothalamic sleep-wake effectors, including lateral hypothalamic (LH) arousal systems (orexin and LHGABA) and sleep-promoting circuitry in the ventrolateral preoptic area (VLPO), to destabilize state control. We propose that acute stress recruits PVN-BNST pathways to promote vigilance, whereas chronic stress induces plastic changes that recalibrates circuit gain and weakens inhibitory "brakes," stabilizing hyperarousal and fragmenting sleep. In this framework, insomnia reflects a failure of state regulation in which PVN-BNST networks reset arousal systems, converting adaptive vigilance into chronic wakefulness and pointing toward mechanism-based, durable therapies.