Animals are not the only creatures who can be literally half asleep. Research shows we experience this, too
By Christof Koch | SA Mind September 2016 Issue
“The repose of the night does not belong to us. It is not the possession of our being. Sleep opens within us an inn for phantoms. In the morning we must sweep out the shadows.”
—Gaston Bachelard, French philosopher, 1960
Flies, birds, mice, dogs, monkeys and people all need to sleep. That is, they show daily periods of relative immobility and lack of response to external stimuli, such as light, sound or touch. This reduced sensitivity to external events distinguishes sleep from quiet resting, whereas the capacity to awaken from slumber distinguishes sleep from coma. Why sleep should be such a prominent feature of daily life across the animal kingdom, despite the fact that it leaves the sleeper unable to confront potential threats, remains mysterious.
Still, much progress in characterizing the physiology and capabilities of the sleeping brain has occurred over the past century, driven by the ability to record electrical activity of the brain (via electroencephalography, or EEG, on the surface of the skull), of the eyes (via electrooculography, or EOG), and of facial or other muscles (via electromyography, or EMG). For scientists, it is this triad of simultaneous measurements that operationally defines the state of sleep, leading to both surprising and counterintuitive insights.
Even without these tools, there are some basic things we do know about sleep. It is essential for our brain to function properly. Most of us have pulled all-nighters or have wanted to sleep but could not, unable to switch off our mind. The next day we are irritable, have trouble keeping our eyes open, and are terrible at tasks that demand sustained attention. Indeed, sleep deprivation causes many traffic accidents—the reason countries have laws that mandate a minimum rest period and maximum working hours for truck drivers.
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