For years, the bone-deep exhaustion of treatment-resistant depression (TRD) was dismissed as a secondary symptom of a mood disorder. However, a landmark placebo-controlled clinical trial from the National Institutes of Health (NIH) has revealed a biological reality: depressed brains suffer from a corrupted sleep engine. Using a two-process model of sleep, the researchers focused on "Process S"—the homeostatic sleep drive that builds up chemical pressure (via adenosine) throughout the day. Under normal conditions, this pressure triggers "synaptic downscaling" during deep non-rapid eye movement (NREM) sleep, which behaves like clearing a computer's cache or turning down the background volume on waking connections. In TRD patients, the internal thermostat for this process is broken, leading to a severe deficit in slow-wave activity (SWA), particular ...