different types of brain waves: Delta waves (below 4 Hz) occur during sleep; Theta waves (4–7 Hz) are associated with sleep, deep relaxation, and visualization; Alpha waves (8–13 Hz) occur when we are relaxed and calm; Beta waves (13–38 Hz) are seen when we are actively thinking and problem solving. Other ranges of brain waves have been identified as important since then, including Gamma waves (39–100 Hz) which are involved in concentrated mental activity, such as reasoning and planning.
