Sleep spindle

A Sleep spindle is burst of brain activity visible on an EEG that occurs during stage 2 sleep. It consists of 12-16 Hz waves that occur for 0.5 to 1.5 seconds.

Uses of Sleep Spindles
Sleep spindles are one of several measures employed by the brain to keep a sleeper in an unconscious state. This pattern is produced during sleep to inhibit the processing of unnecessary information, which would especially interrupt stage 2 sleep. This is why they are defining characteristics (along with K complexes of stage 2 sleep. During deeper stages (3 and 4) subjects are more difficult to awaken (with the exception of the transitory stage 1).