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Sleep cycles: Interruption affects cognition

Drowsy driving is as dangerous as driving while texting or intoxicated because it affects your ability to react and make decisions. The National Highway Traffic Safety Administration has estimated drowsy driving is the cause of approximately 1,550 deaths and 71,000 injuries each year. While they believe the numbers may actually be higher, it is difficult to calculate potentially related accidents because there is no test like the breathalyzer for alcohol detection. In some cases, accidents characterized as alcohol related may have actually been caused by a drowsy driver.

Sleep deprivation and fatigue cause changes in behavior, mood and cognitive performance. Sleep deprivation can also cause negative changes in hormones, metabolism, the immune system and is related to higher rates of obesity, diabetes and cardiovascular disease.

In order for the body to feel rejuvenated and be alert, an adult must achieve quality sleep by completing full cycles of each sleep stage.

Stage I

The first stage begins when your eyes are heavy and you feel as though you are ready to go to bed. It is a transitional period before actually falling asleep where your brain and muscle activity begin to slow. Sometimes you may even experience a sudden drop sensation, which causes your body to jerk.

Stage II

Now you have entered light sleep. At this point, all eye movement stops, the heart rate slows a bit and your body temperature begins to decrease. Brain waves and muscle movement shift from slow to spontaneous bursts and then back to relaxation.

Stage III and IV

Combined, these stages are classified as slow wave sleep. Brain waves slow, blood pressure drops, breathing slows and your core temperature drops lower than before. Additionally, your body is now immobile as you slip into a deeper sleep. With deeper sleep, you also experience no eye movement and it is far more difficult to wake you. If you do wake during these stages, you will feel groggy and disoriented.


No, not the band-rapid eye movement. This stage is far more active. Brain activity increases and your breathing will be rapid, irregular and shallow. At this point, as the acronym suggests, your eyes will begin to dart in various directions. This is the stage where dreams are made. Additionally, your muscles will be temporarily paralyzed which prevents you from physically acting out your dreams.

Combining the stages

Research has shown that an adult needs to experience the right balance of each stage in order to have the full restorative effects sleep is meant to provide. For example, quality sleep through each cycle is believed to assist with learning, memory, mood and concentration.

A full cycle alternates between each stage and REM every 90 to 110 minutes and is repeated four to six times every time you sleep.

Sleep deprivation: Interrupted cycles

Waking in the middle of a sleep cycle, even one night per week, can cause sleep deprivation. An interrupted cycle will require your body to restart each phase, making it difficult to reach deep sleep and benefit from its restorative natures. Without the proper sleep, you will react more slowly and make poorer decisions which will make driving or operating machinery far more dangerous.

Iowa leads the way

Unfortunately, most people think the dangers of drowsy driving come from falling asleep at the wheel. While nodding off certainly can be perilous, drowsy driving includes those who are fatigued and sleep deprived. Even if they don't fall asleep, their driving may be impaired.

Iowa has lead the way in bringing this issue to the forefront with the first annual Drowsy Driving Summit held at the University of Iowa, College of Public Health in June. Dr. Rosekind, an expert on fatigue and the Administrator of the National Highway Traffic Safety Administration, suggested there should be four types of impaired driving classifications: drunk, drugged, distracted and drowsy. While precise counts for crashes, injuries or fatalities are lacking and the numbers are believed to be underestimated, the summit is a step towards bringing awareness to the issue and the importance of making and keeping our roads safe. 

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