What feature is typically absent in a normal waking and sleeping adult EEG recording?

In a normal waking and sleeping adult EEG recording, delta range activity is typically absent during alert states. Delta waves, which are prominent during deep sleep, indicate very slow brain activity and are not typically present when a person is alert and fully awake. Instead, alert states are generally associated with higher frequency waves such as alpha and beta.

When an individual is awake and engaged in tasks, the EEG displays faster frequencies like beta waves, which reflect active cognitive processing and concentration. During relaxation, alpha rhythms appear, reflecting a calm and resting state with eyes closed. Therefore, the absence of delta activity during alertness distinguishes normal waking EEG patterns from those seen in sleep, where delta activity becomes more prevalent.