You are watching sleep researchers monitor the sleep of a normal adult. The participant is hooked up to an EEG. What brain waves would you observe as the person becomes drowsy and then enters the first stage of sleep?

A) alpha eventually replaced by delta
B) delta eventually replaced by theta
C) alpha eventually replaced by theta
D) delta eventually replaced by beta

Answer: C
Rationale: As people begin to shift into sleep, their brain waves start to become slower, larger, and more predictable; these waves are known as alpha waves, and they signal that a person may be daydreaming, meditating, or starting to fall asleep. As people progress further into stage 1 sleep, their brain waves continue to slow down and become higher in amplitude—these are known as theta waves. Delta waves are only seen in deep sleep (stages 3 and 4).