Optimizing the timing of brainwork
This text is part of: "Science of sleep" by Piotr Wozniak (2017)
Optimizing the timing of brainwork
Circadian graph and brainwork
Charting the circadian cycle makes it possible to find the best windows of time for brainwork. The circadian graph below was generated with SleepChart using a log of free running sleep. In the graph, two yellow bands indicate the optimum time for brainwork. The exact timing may differ for each individual. However, the blocks can be easily determined:
- Morning block: soon after waking, after morning coffee, or after breakfast. The best brain slot may last 2-4 hours. If you are sleepy in the morning see: Natural creativity cycle
- Evening block: soon after siesta. The second best brain slot may last 2-4 hours as well. If you do not nap, you may not fully benefit from that block (see: Power nap). If you are sleepy during this slot see: Best time for napping
The graph explains the reasons for which the two brainwork blocks emerge:
Figure: Optimizing the timing of brainwork with respect to the circadian cycle. This graph was generated with the help of SleepChart on the basis of 3-year-long daily measurements of a free-running sleep rhythm. The horizontal axis expresses the number of hours from awakening (note that the free-running sleep cycle period may be longer than 24 hours). Light blue dots are actual sleep episode measurements with timing on the horizontal, and the length on the left vertical axis. Homeostatic sleepiness can roughly be expressed as the ability to initiate sleep. Percent of the initiated sleep episodes is painted as a thick blue line (right-side calibrations of the vertical axis). Adenosine-related homeostatic sleep propensity increases in proportion to mental effort and can be partially cleared by caffeine, stress, etc. Circadian sleepiness can roughly be expressed as the ability to maintain sleep. Average length of the initiated sleep episodes is painted as a thick red line (left-side calibrations of the vertical axis). Mid-day slump in alertness is also circadian, but is biologically different and results in short sleep that does not register as a red peak. Sleep maintenance circadian component correlates (1) negatively with core body temperature, ACTH, cortisol, catecholamines, and (2) positively with: melatonin and REM sleep propensity. Optimum timing of brainwork requires both (1) low homeostatic sleepiness, and (2) low circadian sleepiness. There are two high quality alertness blocks during the day: the first after the awakening, and the second after the siesta. Both blocks are marked as yellow bands below the graph. For best learning, and for best creativity, use these two yellow blocks of time. Caffeine can only be used to enhance alertness early in the optimum brainwork window (brown). Later use will affect sleep (caffeine half-life is about six hours). Optimum timing of exercise is not marked as it may vary depending on the optimum timing of zeitgebers (e.g. early morning for DSPS people and evening for ASPS people). For more details see: Biphasic nature of human sleep
Best brainwork time
The optimum timing of brainwork requires both high homeostatic alertness and high circadian alertness. There are two quality alertness blocks during the day: the first occurs after awakening and the second after the siesta period. Both are marked as yellow blocks in the graph (above). For best learning and best creative results, use these yellow blocks for brainwork. Caffeine can only be used to enhance alertness early in this optimum window. Later use will affect sleep (the half-life of caffeine is about six hours). The optimum timing of exercise may vary depending on your exercise goals and the optimum timing of zeitgebers (e.g. early morning for DSPS people and evening for ASPS people). In this example, the stress block is followed by the exercise block to counterbalance the hormonal and neural effects of stress before the siesta (see: Stress valves). Unmarked white areas can be used for the lunch (before siesta) and fun time unrelated to work in the evening at a time when the ascending circadian sleepiness makes creative work ineffective. That white evening protective zone should be free from stress, alcohol, caffeine, etc. Recommended activities might include fun games, relaxation, TV, reading, family-time, DIY, housework, etc. For inveterate workaholics, less challenging and stress-free jobs might also work ok.
Brainwork is fun only if your brain is ready. Sleep is fun if you are ready. Rest and entertainment feel right only after a productive day. Even a bit of stress can be fun if it is properly dosed and timed. You do not need to be an adrenaline junkie to enjoy your stress and exercise slots. There is little exaggeration in saying that a good understanding of the circadian cycle is the key to a happy and productive day! (see: Formula for happy life).
Natural creativity cycle
In addition to the variables of the circadian cycle, the natural creativity cycle employs the fact that the neocortex operates in several modes determined by local fatigue, creative meandering, and neural optimization in sleep. During the day, natural transitions from high focus to distraction, to high creativity, and to rest will occur in proportion to the engagement of individual areas of the cortex. It will depend on the concept maps involved in the mental computation, and the overall neural activation. At night, the brain will proceed with natural memory optimization by sequentially switching between NREM and REM sleep modes.
For details see: Natural creativity cycle
Balanced 24 hour cycle
The slanting green line separates the graph into the areas of phase advanced (right) and phase delays (left). The line is determined by points in the graph where the waking time (horizontal axis) added to the sleep time (left vertical axis) equals to 24.0 hours. The place where the green breakeven line crosses the red sleep length line determines the optimum balanced sleep cycle of 24 hours. In the presented example, 17.35 hours of waking, added to the expected 6.65 hours of sleep time complete a balanced full 24 hours sleep-wake cycle. The greater the angle between the green and red lines, the harder it is to balance sleep and fit it into the 24h cycle of the rotating earth. In the example, adding waking hours does not shorten sleep much enough to make the balance easy. This implies that a religious adherence to a 17.35 day may be necessary to balance the cycle. However, this shortened waking day may increase sleep latency and increase the probability of premature awakening, which can also tip the balance towards the phase delay. The vertical aqua line shows where the expected sleep time added to the waking time equals to 24 hours (crossover with the green line representing a perfect 24-hour day). In DSPS or ASPS that 24h balance may be hard to accomplish. For example, without medical intervention, only a large protective zone in the evening, early nap (or no nap), and intense morning exercise can help balance the day in DSPS.
Important! This graph is based on data that is true solely for a free running sleep condition. If you use an alarm clock to regulate the timing of your sleep, these measurements and recommendations may not apply! In addition, the timing and amplitude of changes differ vastly between individuals!
Sleeping against your natural rhythm
If you sleep against your natural rhythm you will often experience tiredness or drowsiness that can be resolved by adjusting the sleeping hours. In healthy individuals, the daytime alertness is primarily determined by:
- circadian phase and homeostatic sleepiness
- total sleep time the night before
- amount of slow-wave sleep the night before
- regular adherence to the sleep-wake schedule in preceding days
- sleep deficits accumulated in the preceding days (e.g. REM deficit, SWA deficit, etc.)
All those factors are closely associated with the sleep phase. Free running sleep provides the best way to maximize alertness throughout a waking day. Free running sleep is likely to shift the minimum temperature point from the early morning closer towards the middle of the subjective night. You should notice increased sleepiness before going to sleep and no sleep inertia upon awakening! If you cannot free-run your sleep, it is very important to understand the relationship between your homeostatic and circadian sleep drives as compiled in the table below. In the course of the day, you should move in sync between the yellow areas of the table, i.e. from perfect alertness to maximum sleepiness, and then back to perfect alertness. The gray areas illustrate when your sleep falls out of sync:
| High circadian sleepiness | Low circadian sleepiness | |
| High homeostatic sleepiness | Peak of the night: You are very drowsy and fall into refreshing sleep with latency of less than five minutes | Insomnia: You are tossing and turning in bed. You are very tired but you cannot fall asleep. Your temperature, blood pressure and pulse are raised. Your thoughts are racing
Solution: Wait for the arrival of the circadian phase. Delay going to sleep by 3-6 hours |
| Low homeostatic sleepiness | Hypersomnia: You are drowsy throughout the day despite long sleep hours. Napping does not help. You show minimum energy levels. Your muscles are weak and atonic
Solution: Adjust your sleep phase to your circadian (e.g. try to go to sleep 3-6 hours later) |
Peak of the day: You are alert, energetic, and full of new ideas |