The 90-Minute Ultradian Focus Block
Ride your brain's natural 90-minute cycle to enter deep work tunnels
The brain naturally cycles through 90-minute ultradian rhythms throughout the day and night, alternating between states of high alertness and lower alertness. Rather than fighting this biology, the 90-Minute Ultradian Focus Block harnesses it by structuring deep work sessions around these natural cycles. You set a timer for 90 minutes and commit to a single domain of work with the understanding that focus within that block will not be uniform.
The framework involves far more than just a timer. It encompasses environmental design: positioning your screen at or above eye level (looking up activates brainstem alertness circuits while looking down promotes sleepiness), playing low-volume white noise (all frequencies mixed randomly, which puts the brain in an optimal learning state), and eliminating all interruptions by turning your phone completely off. The cumulative effect of these environmental adjustments is what Huberman calls 'the tunnel' -- a state of deep, satisfying work that releases dopamine and norepinephrine.
Critically, this block is timed to your biology. Using your temperature minimum, you schedule the block during the steepest rise of your daily temperature curve (4-6 hours after temperature minimum). This means your physiology is actively supporting your focus rather than fighting it. Huberman emphasizes that even two of these blocks per day -- just three hours -- likely matches or exceeds the total deep work most people actually accomplish.
- The brain cycles through 90-minute ultradian rhythms of high and low alertness throughout the entire day
- Eye position influences alertness: looking up or at eye level activates brainstem arousal circuits; looking down promotes sleepiness
- Low-volume white noise creates an optimal neural state for learning and sustained attention
- Total elimination of interruptions (phone off, not on airplane mode) is non-negotiable for entering deep focus
- Peak cognitive performance aligns with the steepest rise of your daily body temperature curve
- Calculate your optimal start timeAdd 4-6 hours to your temperature minimum (average wake time minus 2 hours) to find your peak focus window. If you wake at 7 a.m., your temperature minimum is 5 a.m., so your ideal block starts between 9 and 11 a.m.Pro tipIf you naturally feel sharp immediately upon waking, honor that and schedule the block earlier. This formula is a guideline, not a prison.
- Configure your physical workspacePosition your screen at or slightly above eye level. This leverages the brainstem-eye connection that increases alertness when your gaze is directed upward. Most people work with screens angled 30 degrees below eye level, which actively promotes drowsiness.Pro tipA simple laptop stand or stack of books can raise your screen to the correct height for almost no cost.WarningDo not look down at a phone or tablet on your lap during this block. The downward gaze will undermine alertness regardless of how interesting the content is.
- Set your environment and timerTurn your phone completely off. Play low-volume white noise. Set a 90-minute timer. Accept that the first portion of the block will involve your brain settling in -- you will not be immediately locked in, and that is normal.Pro tipHuberman emphasizes that the phone must be off, not on airplane mode. The psychological knowledge that it could ring or buzz is itself a distraction.WarningDo not use music with lyrics or structured melodies. White noise works because it is all frequencies with no pattern for the brain to track.
- Work through the full 90 minutesCommit to a single domain of work for the entire block. Your focus will rise and fall within the 90 minutes -- this is the ultradian cycle at work, not a failure of discipline. The goal is to find and stay in 'the tunnel' as long as possible.Pro tipOn days where focus is difficult, remind yourself that the neurochemical reward (dopamine, norepinephrine) comes after the block, creating a sense of deep satisfaction similar to completing a workout.
- Exit cleanly and schedule the second blockWhen the timer ends, stop. Transition to physical exercise or a different type of work. Plan a second 90-minute block later in the day for less demanding work. Combined, two blocks yield approximately 3 hours of genuine deep work -- likely more than most people achieve.Pro tipUse the transition between blocks for physical exercise. The movement helps consolidate what you learned during the focus block and resets your neurochemistry for the next cycle.
A freelance writer habitually procrastinates for hours before writing, checking email and social media until deadline pressure forces productivity. He implements the ultradian block by calculating his 10 a.m. optimal window, raising his laptop on a stand, playing white noise, and powering off his phone. The first three days, he struggles for the first 20 minutes of each block before settling in.
A product manager realizes that her entire day is consumed by meetings and Slack messages, leaving zero time for strategic thinking. She blocks 9:30-11:00 a.m. on her calendar as a non-negotiable focus block, tells her team she is unreachable during that time, and uses the environmental setup (screen height, white noise, phone off) to enter deep work on product strategy documents.
A medical student with an average wake time of 8 a.m. calculates his temperature minimum at 6 a.m. and schedules his hardest study material (anatomy, pharmacology) for the 10 a.m.-11:30 a.m. window. He reserves afternoon study for review and lower-intensity material.
The ultradian cycle was first documented in sleep research, where scientists observed that sleep stages cycle in roughly 90-minute intervals. Later research revealed that this same rhythm persists during waking hours, governing attention and alertness fluctuations. Huberman synthesized this chronobiology with his knowledge of the visual system's role in alertness (eye position affecting brainstem arousal) and auditory neuroscience (white noise's effect on neural readiness) to create a comprehensive environmental protocol for deep work.
He describes his own 90-minute work block as 'kind of holy' and notes that the satisfying feeling upon exiting it is likely driven by dopamine and norepinephrine release -- the same reward chemicals that make exercise feel good. This positions the protocol not as willpower-dependent discipline but as a neurochemically rewarding practice that becomes self-reinforcing over time.