[Effects of caffeine on physiological parameters during a learning test]

Several physiological variables were continuously monitored concomitantly to performance in a conceptual learning paradigm in 48 men before and after oral administration of 300 mg caffeine in decaffeinated coffee vehicle (N = 16) or control administrations consisting of decaffeinated coffee alone (N = 16), warm water (N = 8), or no beverage (N = 8). In a stepwise discriminant analysis, only an increased vasoconstriction obtained from the index finger in the caffeine-treated subjects distinguished the caffeine-treated group from the control groups. For this dose of caffeine, the R-R interval of the electrocardiogram, respiration, skin conductance change, and electromyographic response failed to differentiate the various treatment groups. Furthermore, caffeine administration did not affect conceptual learning in the test situation used although it decreased variance of performance in a continuous letter cancellation task.