Which brain waves are associated with deep sleep?

Delta waves are the brain waves that are predominantly associated with deep sleep. These waves are characterized by their slow frequency, ranging from about 0.5 to 4 Hz. During deep sleep, which is also referred to as slow-wave sleep, delta waves are most prominent. This phase of sleep is crucial for physical restoration, growth, and immune function, and is considered one of the most restorative stages of the sleep cycle.

In contrast, alpha waves are more associated with a relaxed but awake state, often seen when one is in a calm and meditative state. Beta waves, with their faster frequency, are associated with active thinking, alertness, and engagement in tasks. Theta waves occur during light sleep and deep relaxation, such as during dreaming, but they do not characterize the deepest sleep stages. Hence, delta waves are the hallmark of deep sleep, making them the correct answer.