Acute autonomic nervous system effects of caffeine in prepubertal boys.

The effects of caffeine on autonomic activity were tested in 19 normal prepubertal boys. Subjects received placebo, 3 mg/kg, and 10 mg/kg caffeine in a random order (double blind) before three test sessions 48 h apart. Skin conductance (SC), heart rate (HR), and skin temperature (ST) were recorded during a rest period, a series of nonsignal tones, and a simple reaction time (RT) task. Caffeine increased the frequency of both spontaneous and elicited SC responses (SCR) under all conditions. Resting SC base level (SCL) was increased, and shorter SCR half recovery time also occurred in some periods. In contrast, caffeine decreased HR and motor activity at 3 mg/kg. Evidence of improved attention on caffeine was also obtained. The physiological effects are partially similar to the effects seen in clinical anxiety states, and they are also consistent with the physiological concomitants of good sustained attention. The profile of effects did not resemble those of dextroamphetamine in a similar population.