CAFFEINE DELAYS HABITUATION OF THE HUMAN ACOUSTIC STARTLE REFLEX

The acoustic startle reflex has proved to be an excellent system for studying habituation in mammals. In animal studies, startle habituation has been found to be sensitive to various pharmacological manipulations. The present experiments were designed to determine whether caffeine (4 mg/kg) modified startle habituation in low and high caffeine users. Human eyeblink responses were measured in a startle habituation paradigm in which 30 trials of 85-dB broadband noise stimuli with a duration of 50 msec and a rise time of .1 msec were presented. Caffeine delayed the habituation of startle amplitude in both low and high users and produced significant dishabituation in low users. These findings indicate that caffeine disrupts early sensory filtering.