Re: why we are only able to sleep with our eyes closed?

Dear Vivek,

Although we almost always sleep with our eyes closed, people can and do sleep with their eyes open.

Sleep is generally defined by the presence of certain types of electrical activity in the brain. When people are awake, the electrical activity of their brain, as measured by an electroencephalogram, is desynchronized and of low amplitude. As a person enters sleep, the pattern of their brainwaves changes from low amplitude, higher frequency waves to higher amplitude, lower frequency waves. Additionally, sleep is subdivided into different stages. These stages are defined by the frequency and amplitude of the electrical waves being generated by brain activity, and are also related to easily how a person can be aroused by an external stimulus. Finally, there is a separate stage of sleep called rapid eye movement (REM) sleep, which is characterized by a more "awake" looking brain wave pattern, eye movements, and dreaming.

Usually, when we sleep, our eyes are closed. In my view there are 2 primary reasons for this. First, distracting sensory stimuli (lights, noises, etc.) can interfere with sleep, and closing your eyes greatly reduces visual input. Second, closing your eyelids protects your eyes from foreign objects and from drying out during sleep.

That said, there are instances in which people may be asleep with open eyes. One good example is sleepwalking. Usually, a sleepwalker will initially get out of bed and walk around the room with their eyes open. As the episode continues, their behavior can get very complex. They can avoid objects, go to the bathroom, even clean the house. All during this time, an electroencephalogram would indicate that this person is completely asleep. I would imagine you could also see this sort of phenomenon in someone who had been sleep deprived for a long period of time. They might at times appear behaviorally awake when their brain wave patterns are sleep-like.

This observation actually poses a very interesting question: How are people able to carry out complex motor tasks when they are asleep? I invite anyone that has some serious thoughts on this idea to send me an email.