CAFFEINE DELAYS HABITUATION OF THE HUMAN ACOUSTIC STARTLE REFLEX

The acoustic startle reflex has proved to be an excellent system for s tudying habituation in mammals. In animal studies, startle habituation has been found to be sensitive to various pharmacological manipulatio ns. The present experiments were designed to determine whether caffein e (4 mg/kg) modified startle habituation in low and high caffeine user s. Human eyeblink responses were measured in a startle habituation par adigm in which 30 trials of 85-dB broadband noise stimuli with a durat ion of 50 msec and a rise time of .1 msec were presented. Caffeine del ayed the habituation of startle amplitude in both low and high users a nd produced significant dishabituation in low users. These findings in dicate that caffeine disrupts early sensory filtering.