Sleep and Fatigue — Page 210, Lesson 339

I want to walk you through the two main types of sleep that make up a typical night's rest — slow wave sleep, also called orthodox sleep, and rapid eye movement sleep, which we call REM sleep. These are essential concepts for you as a pilot because your alertness, memory, and emotional state all depend on getting the right balance of both. Let's start with slow wave sleep. Its function is to refresh the body and support tissue restoration. If you've had a day of strenuous physical activity — say, heavy manual work or intense exercise — your body will actually demand more slow wave sleep that night to repair and rebuild. That's why it's sometimes called orthodox sleep: it's the deep, restorative sleep that physically rebuilds you. Now, superimposed on top of the four stages of sleep — and I should mention that slow wave sleep covers those deeper stages — we have REM sleep. REM is sometimes referred to as paradoxical sleep, and the name tells you why: it's quite different from orthodox sleep. In this phase, the brain is highly active. In fact, the EEG trace — that's the electrical recording of brain activity — looks similar to someone who is fully awake. Yet at the same time, all the other measurements show the person to be asleep. That's the paradox: a wide-awake brain inside a sleeping body. There are several key features of REM sleep. First, rapid eye movements are detected behind the eyelids — that's where the name comes from. Second, while there is near-total muscle paralysis throughout most of the body — this is thought to prevent you from physically acting out your dreams — the muscles of the eye are frantically moving. Occasionally, that motor activation breaks through, and you might see twitching of the limbs. Third, this is when complex, bizarre, and emotionally-coloured dreams take place. So what is the function of REM sleep? It refreshes the brain. It strengthens and organizes memory. If you've spent a period learning new tasks or procedures — which, as a pilot trainee, you will be doing constantly — your REM sleep will actually increase to help consolidate that learning. In addition, REM sleep contributes significantly to emotional equilibrium and good humour. That's why after a period of disrupted sleep, irritability normally follows — you've missed out on the REM that keeps your emotions balanced. So to summarise what we've covered: slow wave sleep restores your body, and REM sleep restores your brain and memory. Both are critical for you to perform safely and effectively in the cockpit.