Leo is participating in a sleep study. During his sleep, his brain shows delta wave activity. At that point, the researchers wake him up, and he is very disoriented. When the researchers wake Leo up, he is most likely in sleep. a. stage 2 b. REM c. stage 1 d. slow-wave

Before jumping to the solution, it is beneficial to know fundamental details about different sleep stages: 1. Stage 1: This is the light stage of sleep, also known as drowsy sleep. Here, the brain produces high amplitude theta waves. 2. Stage 2: Light sleep. The body temperature and heart rate start to decrease. Brain starts producing sudden increase in brain wave frequency known as sleep spindles. 3. Slow-wave sleep (SWS): Also known as deep sleep. During this stage, the body repairs muscles and tissues, stimulates growth and development, boosts immune function, and builds up energy for the next day. Slow-wave sleep shows delta wave brain activity. 4. REM (Rapid Eye Movement) Sleep: Known as dream stage sleep when most dreaming occurs. Brainwaves during this stage are similar to brainwaves when we are awake.

Knowing that delta waves are associated with Slow-wave sleep, we can identify that Leo was likely in this stage when he displays delta wave activity. Therefore, the correct answer is: d. slow-wave