The biology behind this is actually wild.Your brain tracks sleep debt in a molecule called adenosine. Every hour you're awake, adenosine builds up and binds to receptors that slow neural firing. Coffee blocks those receptors temporarily but doesn't clear the adenosine. It's still accumulating behind the wall.After 2 hours of sleep, you've cleared maybe 15% of last night's adenosine load. Caffeine holds the rest back until roughly 6-8 hours after your last cup, when the receptors open back up and