What is a Brain Wave?

An illustration showing sleep brain waves.
An illustration showing sleep brain waves. Michel Tcherevkoff/Getty Images

A brain wave is the summation of the electrical activity of numerous neurons as can be recorded by an EEG. These rapid fluctuations of voltage occur between various parts of the brain. These electrical patterns are described as having a given frequency, amplitude, and shape. They can be used to assess level of consciousness or sleep stage.

Stages of Sleep

The electrical patterns of brain waves can be used to assess the various states of sleep. Sleep occurs in two basic states throughout the night. The two stages of sleep are rapid eye movement sleep (REM) and non rapid eye movement sleep (NREM).

Rapid Eye Movement Sleep (REM)

REM sleep, also known as dreaming sleep, is a deep stage of sleep with intense brain activity in the forebrain and midbrain. It is characterized by dreaming and the absence of motor function with the exception of the eye muscles and the diaphragm. It occurs cyclically several times during sleep, but it comprises the smallest portion of the sleep cycle.

During REM sleep, there are changes in blood pressure, heart rate, and overall breathing rate. Also during REM sleep, blood flow becomes increased to the brain, as well as the penis and clitoris, which results in engorgement.

Non Rapid Eye Movement Sleep (NREM)

REM sleep is one of the two basic states of sleep. The other basic state of sleep is non rapid eye movement sleep, or NREM sleep. Arousal occurs more often during NREM sleep, which consists of three separate stages. The three stages are N1, N2, and N3, and each separate state has unique, distinct, and recognizable electrical brain wave patterns. While REM sleep is the deepest state of sleep, NREM sleep takes up the largest portion of the overall sleep cycle.

Non rapid eye movement sleep is typically characterized by a decreased amount of blood flow to the brain and the skeletal muscle. Other characteristics of non rapid eye movement sleep include decreased heart rate, blood pressure, and total volume of air cycling in and out of the lungs.

Brain Wave Arousal

Arousal is an abrupt change in the pattern of brain wave activity, as measured by an EEG. Arousal typically represents a shift from deep sleep, which is commonly known as REM sleep, to light sleep, known as NREM sleep, or from sleep to wakefulness.

As it sounds, arousal is when a person becomes "aroused" to some extent during the sleep cycle. It is a sudden change in brain wave activity. It does not necessarily mean that the person has woken entirely, but could just mean a shift out of extremely deep sleep to a lighter sleep, from which it is easier to be woken up.

Examples: The pattern of brain wave activity shows that he is in deep sleep.

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