REM sleep is initiated by a rise in _____, which activates the cerebral cortex while the rest of the brain remains relatively inactive.

A) serotonin
B) norepinephrine
C) acetylcholine
D) cortisol

REM Sleep

A phase of sleep characterized by rapid eye movement, during which most dreaming occurs, and is considered important for cognitive functions like learning and memory.

Acetylcholine

A neurotransmitter involved in many functions including muscle movement, heart rate, memory, and the modulation of sleep cycles.

Cerebral Cortex

The outer layer of the brain's cerebral hemispheres, involved in complex functions including sensory perception, thought, language, and consciousness.