Neurotransmitter Adenosine, produced by brain metabolism during waking, has an inhibiting effect on the neurons in the pons that produce EEG arousal. Adenosine is produced as a by-product of brin activity, which higher during wake than sleep. Has an inhibitory effect on the neurons that maintain arousal as measured by the EEG, thus leading eventually to lowered arousal & sleep. Caffeine in coffee & theophylline in tea block receptor sites for adenosine, accounting for arousal properties of coffee & tea.