Essentials: Time Perception, Memory & Focus

Andrew Huberman, who introduces himself as a professor of neurobiology and ophthalmology at Stanford School of Medicine, frames time perception as a major influence on how people evaluate their lives. Its connection to mood, stress, happiness and excitement helps shape judgments about the past, whether the present feels on track, and expectations for the future. He begins with entrainment: the linking of internal biological and psychological processes to something outside the body.

At the annual scale, Huberman describes circannual rhythms as a biological calendar. His explanation centers on melatonin: light reaching the eyes inhibits its release, while shorter days tend to allow greater and longer-lasting release. He assigns melatonin two major functions—promoting sleepiness at night and regulating other hormones, particularly testosterone and estrogen. The brain and body, he says, integrate exposure to both sunlight and artificial light, producing a signal that reflects changing light conditions over time.

The direction of seasonal change matters in his account. He contrasts an eight-hour day during a period when days are lengthening with an eight-hour day when days are shortening: melatonin is progressively decreasing in the first situation and increasing in the second. He uses this distinction to explain why most people, though explicitly not everyone, experience more energy in spring and less energy or lower mood in winter. He also connects the seasonal signal to appetite and says humans tend to produce more testosterone and estrogen during longer days than during shorter days. These are presented as general tendencies with individual exceptions.

Huberman next moves to circadian rhythms, describing a clock above the roof of the mouth that coordinates a repeating cycle of roughly 24 hours. Alongside this central clock, he says, every cell has daily oscillations in the expression of various genes. Morning sunlight, evening sunlight and darkness during the middle of the night help align these internal changes with the external light-dark cycle. In his framing, circadian entrainment supplies the daily timing structure for activity, alertness and sleep.