Why Does Andrew Huberman Feel Alert After an All-nighter?

Andrew Huberman says two forces decide sleepiness and wakefulness. The longer someone stays awake, the more adenosine accumulates in the brain. Adenosine binds to adenosine receptors and creates sleepiness, independent of time of day or night. How sleepy a given amount of adenosine feels also depends on a body-temperature cycle. Huberman calls the cycle a well-conserved oscillation that takes 24 hours, plus or minus an hour. He does not think alignment with the 24-hour spin of the Earth is a coincidence. Sunlight covers one portion of the spin and darkness covers the other.

On a schedule of days awake and nights asleep, temperature is lowest around 3 a.m. or 4 a.m. It creeps up through the morning, peaks in the late afternoon, then drops toward evening. Staying up for 24 hours pulls the two forces apart. On the regular schedule Huberman follows, he gets very sleepy around three or four in the morning after staying past midnight, 2 a.m., and 3 a.m. Around five, six, or seven in the morning, his normal wake-up time, he feels more alert even though adenosine has kept accumulating. Adenosine is higher the longer he stays up, yet he feels more alert than a few hours earlier, because the temperature cycle has swung back toward wakefulness.

Adenosine makes you sleepy. The 24-hour temperature oscillation decides how sleepy or how awake you feel.