INHIBITION OF STARTLE REFLEX IN RAT BY PRIOR TACTILE STIMULATION

Groups of rats (3) received a tactile prepulse 0.5, 1 or 2 mA electric shock (to feet) .25, .5, 1, 5, 10 or 20 s prior to an acoustic startle stimulus. The startle response was maximally inhibited at the .25 s interval and gradually recovered thereafter. Inhibition was larger with the intense stimuli and for the .5 mA stimulus occurred reliably only in animals which responded to the prestimulus. The intensity of the prepulse was varied within subjects at intervals of .5, 1 and 2 s. Inhibition was directly related to prestimulus intensity and was greatest at .5 s. An EMG [electromyogram] measure of startle reactivity allowed the use of shorter intervals. The maximal inhibitory interval between the prestimulus and startle stimulus was 40 ms compared with a shorter 10 ms or a longer 250 ms separation.