“To put it simply, fast brainwaves correspond to states of alertness and focus. Slower brainwaves correspond to states of imagination, daydreaming, or simply sleepiness.
It turns out your brain needs to go into the “slow” state once in a while. Staying 100% focused for several hours straight is unsustainable, if not flat out impossible.
Each brain cell uses sodium and potassium ions for electrical signals. After several minutes (or hours) in fast brainwave states, the sodium and potassium ions become “depleted” (for lack of a better word).
Studies have shown that the brain can restore the sodium/potassium balance by going into slow brainwave states.
Your body comes designed with a clever mechanism called the “ultradian rhythm”, which is also known as the “Basic Rest and Activity Cycle” or BRAC.
The BRAC repeats itself every 90-120 minutes. During the first half of the BRAC your brain is in a fast brainwave state. You feel focused and alert. During the last half, your brainwaves start to slow down. And for the last 20 minutes of the BRAC, you will feel daydreamy, and perhaps a bit tired. This is good, because it’s a sign your brain is restoring the sodium/potassium balance, so that once the 20 minutes of rest are up, you’ll be able to rebound back into fast brainwaves states.
As you’re reading this right now, you are transitioning through a high or a low of your BRAC. If you feel focused and alert, you’re probably in the first 70-100 minutes of the cycle. If you feel daydreamy and are unable to focus, you might be in the last 20 minutes.
“Understanding this Basic Rest and Activity Cycle is one of the key elements to unlocking your brain’s potential and sustaining mental energy levels throughout the day.” – Optimal Sleep Series #6
You can take advantage of your natural undulations in wakefulness. This is actually the origin of polyphasic sleep, physiologically. When people are at leisure or in a state of extreme stress they will naturally take naps when there is a drop in wakefulness.
When you are sleeping your body’s BRAC will manifest itself as stages of sleep. Instead of increasing in brain wave frequency over the first half of the cycle it will decrease in brain wave frequency (going from light to deep sleep) then rise and finish with a period of REM sleep.
The uberman schedule is the prime example of the Basic Rest and Activity Cycles in action under stress. The ultradian rhythm locks in at 120 minutes and after some learned behaviour can expand out into multiples of this time, 240 minutes (and in cases such as everyman, 360-390 minutes).
Hopefully this helps you understand the origin of the 4 hour cycle, as 4 hours is two 2 hour BRACs.
You can lock your ultradian rhythm into any length within the natural BRAC range, so a 4 hour cycle is not the only cycle you can have. You could train yourself to have a 3h cycle (2x 90 min BRACs), or a 3.5h cycle (2x 105 min BRACs) quite naturally.
The brain transits from a Beta frequency state to an Alpha state at the end of each BRAC, and if you use certain techniques, such as meditation, or WILD, or even just closing your eyes for sleep, you can further sink into slower frequency brain-wave states, or instead transition into REM. This may seem like an article of obvious statements, but it paves the way to further investigation into the science of polyphasic sleep!