The Ultradian Rhythm: Working With Your Brain's Natural Cycles

We are familiar with the circadian rhythm — the 24-hour biological clock that governs when we sleep and wake. But there is another biological rhythm that most of us have never heard of, and that shapes our mental performance and wellbeing just as profoundly: the ultradian rhythm.

What Is the Ultradian Rhythm?

Ultradian rhythms are cycles shorter than 24 hours that repeat multiple times throughout the day. The most significant, from a brain performance perspective, is the 90–120 minute cycle first identified by sleep researcher Nathaniel Kleitman — the same researcher who discovered REM sleep.

Kleitman noticed that the 90-minute REM cycles that occur during sleep do not stop when we wake. They continue throughout the day as alternating periods of higher and lower alertness — roughly 90 minutes of focused activity followed by a 15–20 minute period of relative rest and consolidation.

The High-Performance Phase

During the high phase of the ultradian cycle, the left hemisphere is typically dominant. The brain is primed for focused, linear, analytical work: reading, writing, detailed thinking, decision-making, conversation. This is when the brain is most efficient at processing new information.

The nervous system is in a relatively sympathetic state — alert, energised, directed. Physical performance is also at its peak during this phase.

The Rest Phase

Around the 90-minute mark, the brain begins to signal that it needs a break. Concentration dips. Daydreaming increases. There may be yawning, restlessness, a slight loss of motivation. These are not signs of laziness or weakness — they are biological signals that the brain needs to consolidate what it has processed and restore its capacity.

During this phase, the right hemisphere becomes relatively more dominant. The mode shifts from linear to associative, from focused to diffuse. This is when creative insights often arise. It is also when the body's self-repair mechanisms are most active.

What Happens When We Override the Cycle

Modern culture strongly encourages — or demands — that we override the rest phase. Push through. Stay focused. Don't stop. The result is a cumulative dysregulation: the nervous system stays in sympathetic overdrive, consolidation of learning doesn't happen efficiently, creativity is suppressed, and the body accumulates stress that doesn't discharge.

Over time, this contributes to burnout, cognitive decline, emotional reactivity, and a reduced capacity for genuine rest — even when we finally stop, sleep doesn't repair what chronic override has damaged.

Working With the Rhythm

Understanding the ultradian rhythm suggests a simple but powerful shift in how we organise time. Instead of working in long, uninterrupted blocks and wondering why productivity falls off a cliff by mid-afternoon, we structure our work in 90-minute sessions with intentional breaks in between.

The break matters. Not a scroll through a phone — that keeps the left hemisphere engaged and prevents the rest phase from functioning. A genuine rest break: eyes closed, body relaxed, perhaps a short walk, perhaps a brief meditation, perhaps simply sitting quietly for 10–15 minutes and letting the mind wander.

The Ultradian Rhythm and Healing

There is a fascinating relationship between the ultradian rhythm and therapeutic processing. The brain's consolidation phase — the rest phase — is when new information (including the shifts that occur in therapy) is integrated. Rushing from a therapy session directly into demanding cognitive work can interrupt this integration. Many practitioners recommend building rest time into the hours following a session.

PACE, practised in the morning, aligns with and supports the ultradian rhythm by establishing nervous system coherence before the first high-performance cycle begins. When the nervous system starts the day regulated, the ultradian cycles tend to be more regular, the rest phases more genuinely restorative, and the overall capacity for learning and recovery greater.

A Simple Practice

Try working in 90-minute blocks today. Set a timer. When it goes off, stop — even if you're in the middle of something. Take 15 minutes of genuine rest. Then return. Notice what happens to your quality of attention, your energy, your creativity across the day.

The body knows how to work. It is asking us to trust its rhythms.