Startle reflex inhibition in the rat: Its persistence after extended repetition of the inhibitory stimulus.

Startle reflexes to intense sound bursts are inhibited by weak stimuli that briefly precede their elicitation. In 3 experiments, with 36 Long-Evans hooded rats, the startle stimulus (a 110-db tone burst) was presented 100 msec after the final link in a train of stimuli, the length of the train varying from 1 to 1,000, its repetition rate varying from 1 to 10 per sec, and its constituents being 40 db or 50 db white noise bursts of 25 msec duration. Inhibition was invariant across train length and repetition rate. In Exp IV, the startle stimulus was presented a variable interval after the final link, from 40 to 1,280 msec with 1 or 100 noise bursts (50 db) in the train. Inhibition developed more rapidly following the last member of the 100-stimulus train, suggesting a "priming" or sensitization effect of stimulus repetition, but its overall strength and subsequent rate of decay were not different in the 2 conditions. The general persistence of inhibition following these extended series of stimuli reveals that reflex inhibition must be the outcome of a fixed and obligatory process associated with sensory input. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)