Theta waves are primarily seen during which phases of sleep?

Theta waves are primarily associated with the lighter stages of sleep, specifically in NREM Stage 1 and during REM sleep. During NREM Stage 1, which is the transition from wakefulness to sleep, theta waves begin to appear as the brain starts to enter a sleep state. This stage is marked by a decrease in activity in the brain, and theta waves reflect this state of relaxation and drowsiness.

In REM sleep, which is characterized by rapid eye movement and increased brain activity similar to that of waking states, theta waves are also prominent. This phase of sleep is critical for various cognitive functions, including memory consolidation and emotional processing, and the presence of theta waves indicates a brain that is actively processing information, despite the person being in a sleeping state.

While the other stages of NREM sleep, particularly Stage 2 and Stage 3, have distinctly different brain wave patterns (with Stage 2 featuring sleep spindles and Stage 3 featuring delta waves), the combination of theta waves during NREM Stage 1 and REM sleep signifies transitional and active dreaming phases of sleep. Thus, this makes the first option the correct choice, highlighting the presence of theta waves during those specific sleep states.