US High School Psychology Complete Practice Exam 2026

Serotonin is the correct answer as it plays a significant role in regulating sleep patterns. It is a neurotransmitter that influences various functions in the body, including mood and the sleep-wake cycle. During the evening, serotonin levels are believed to decrease, which helps facilitate the onset of sleep. Additionally, serotonin is a precursor for melatonin, another hormone that regulates sleep. By contributing to the biological mechanisms that govern sleep, serotonin highlights its importance in maintaining healthy sleep cycles.

Norepinephrine, dopamine, and glutamate, while important neurotransmitters in the brain, do not primarily function in sleep regulation. Norepinephrine is generally associated with arousal and alertness rather than sleep. Dopamine is involved in reward and motor control, while glutamate functions mainly as a neurotransmitter that promotes excitatory signaling in the brain. Therefore, serotonin stands out for its specific role in influencing sleep.