Time Perception & Entrainment by Dopamine, Serotonin & Hormones

KEYPOINTS

• 01

  Circannual rhythms run on melatonin, which tracks day length

  Light hitting the eyes suppresses melatonin; flipping on a bright bathroom light at night can drop it close to zero. Because the brain averages light exposure across days, long spring days mean progressively less melatonin and short winter days progressively more. Melatonin also regulates testosterone and estrogen, which is why most (not all) people feel more energy in spring and lower mood and energy in winter.

• 02

  Skin acts as a hormone-influencing organ that responds to sunlight

  Huberman cites Parikh et al. in Cell Reports: across the year, people made more testosterone and estrogen in longer days, correlating with romantic desire, combativeness and overall mood. About 2 hours a day of sunlight on exposed arms, upper back, neck and face drove significant increases, even with cloud cover, and sunscreen did not appear to block it. He notes skin health and cancer risk still take priority.

• 03

  Every cell carries a 24-hour gene–protein timer

  Clock genes such as Per, Bmal and Clock are expressed, make a protein that shuts the gene off, and restart once the protein is used up, a loop that takes about 24 hours. Morning light, evening light and darkness at night keep these cellular clocks locked to the outside world. Huberman stresses that poor circadian entrainment is linked to higher cancer and obesity risk, mental health problems, slower wound healing, worse performance and hormone disruption.

• 04

  Losing circadian cues degrades time perception at every scale

  In Aschoff's classic 1985 isolation experiments, repeated many times since, people kept without clocks, windows or regular light underestimated their stay: after about 42 days they guessed 28 or 36. Their ability to count off short intervals such as 2 minutes, normally accurate within 5–15 seconds, also fell apart, and Huberman links accurate interval timing to task performance.

• 05

  Focus comes in roughly 90-minute ultradian blocks that you can start whenever you choose

  Nathaniel Kleitman's basic rest–activity cycle governs sleep and also waking focus. Sleep cycles are hardwired, but a waking work cycle starts when you decide it does. Regardless of who you are, focus drops off around 100–120 minutes, because acetylcholine, dopamine and norepinephrine release can't be sustained. Huberman says you shouldn't expect to drop into deep focus immediately.

• 06

  Time perception comes in three modes

  Present-moment perception works like an interval timer, either fine-slicing time or ticking slowly. Prospective timing is a stopwatch running forward, where you have to decide how many tick marks to set for, say, 5 minutes. Retrospective timing reconstructs the past from memory, such as working out the gap between lunch and dinner last week. Each mode is shaped by neuromodulators.

• 07

  Dopamine and norepinephrine raise your perceptual 'frame rate', so you overestimate elapsed time

  When drugs raise dopamine, people asked to mark one minute call it at around 38 seconds. Huberman compares this to filming at 4,000 instead of 30 frames per second: more frames make events look slower. Norepinephrine, which is made from dopamine, has a similar effect.

• 08

  Serotonin lowers the frame rate, so you underestimate elapsed time

  In human studies using serotonin-raising drugs and cannabis, people asked to mark 5 minutes let about 6 pass. Huberman says the evidence suggests dopamine and norepinephrine dominate the first half of the waking day and serotonin rises toward evening, with early evidence that people overestimate time passing in the morning and underestimate it later.

• 09

  Trauma can 'overclock' memory

  Extreme arousal pushes dopamine and norepinephrine so high that events are experienced in ultra-slow motion. The hippocampus stores both which neurons fired and the rate at which they fired, so these memories are stamped in at high resolution and are hard to shake. Huberman says treatments such as EMDR, exposure therapy, CBT and newer ketamine approaches partly work by giving the person control over how fast the memory plays back, which helps separate the emotional weight from the memory.

• 10

  Dopamine release marks the boundaries of your experienced time bins

  Dopamine signals both expected rewards and surprises, positive or negative. Huberman argues that how often dopamine is released sets how you carve up the day into segments, which turns habits into time markers as well as sources of motivation.