Sleep and the EEG

Electroencephalography (EEG) is a valuable diagnostic tool for physicians and researchers in the Boston area. One of the areas of science and medicine in which the EEG is extensively used is in the study of sleep and sleep disorders. Sleep is divided into phases, which are identifiable by the patterns observable on EEG recordings. Sleep stages are divided into REM (rapid eye movement) and NREM (non-rapid eye movement) sleep, with NREM further divided into three stages.

NREM Stage 1

Stage 1 NREM sleep, is a phase in between sleep and wakefulness. On an EEG, stage 1 sleep is associated with a transition in the brain from alpha waves (8-13 Hz) to theta waves (4-7 Hz). During this stage, a person’s muscle tone decreases and they lose most of their consciousness of the external environment.

NREM Stage 2

In Stage 2 NREM sleep, conscious awareness of the external environment disappears completely, although a person can be roused from stage 2 sleep fairly easily. In EEG recordings of people in stage 2 sleep, two distinctive patterns can be observed: sleep spindles and k-complexes. Sleep spindles consist of 12-14 Hz waves that last for about half a second. Scientists in Boston theorize that sleep spindles represent the brain inhibiting certain processes that might otherwise interrupt sleep. K-complexes consist of a brief, high-voltage peak followed by a slower complex. They occur every 1.0-1.7 minutes and are often followed by sleep spindles. They can occur spontaneously, but also occur in response to external stimuli such as sounds.

NREM Stage 3

Stage 3 NREM sleep in Boston is also called “slow-wave sleep” or “deep sleep.” The transition from Stage 2 to Stage 3 is marked by an increase in delta waves, which come to predominate during slow-wave sleep. EEG activity is synchronized, and consists of low-frequency, high-altitude wavelengths. Dreaming sometimes occurs in Stage 3 NREM sleep, although it is less common than in REM sleep. Slow-wave sleep is believed to be associated with consolidating memories within the brain.

REM Sleep

REM (rapid eye motion) sleep is characterized by rapid, random movement of the eyes. It generally comprises 20% to 25% of total sleep in adults, occurring in four or five periods during the night. Infants spend as much as 80% of their sleep time in REM. It is during REM sleep that dreams are most likely to occur. On an EEG, REM sleep can be seen to involve higher-frequency, lower-amplitude neural oscillations than NREM stages of sleep. REM EEG patterns are also more random and variable than EEG patterns during NREM sleep. Currently, evidence suggests that REM sleep may be important for consolidating procedural and spatial memory, whereas slow-wave sleep is more strongly associated with consolidating declarative memory. REM sleep is also thought to play a significant role in neural development, especially in infants.

EEG FOR INSOMNIA IN BOSTON