Which neurotransmitter is associated with arousal reactions or inhibitory factors in the brain?

• A. Acetylcholine
• B. Dopamine
• C. Norepinephrine
• D. GABA

Answer: (A)

A key neurotransmitter for arousal and the tuning of cortical activity is acetylcholine. Neurons that release acetylcholine in the basal forebrain and brainstem project widely to the cortex and thalamus, promoting desynchronized, wakeful brain activity and sharpening attention and learning. This system helps switch the brain into an alert state and also participates in regulating sleep–wake transitions, including REM sleep. In some circuits, acetylcholine can produce inhibitory effects depending on the receptor types and neural context, illustrating how a single transmitter can modulate activity in diverse ways. While other transmitters contribute to arousal or inhibition in different ways (norepinephrine with general alertness, GABA as the primary inhibitor, dopamine in motivation and reward), acetylcholine is most directly tied to arousal through its widespread cortical modulation and state-switching role.