Startle reaction to electrical shock in the rat.

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Abstract
Equipment was developed to assess the abrupt movement which characterizes the startle reaction. Response amplitude and frequency both increased as a function of shock intensity. Latency increased with decreases in intensity. There was no evidence of inhibition when stimuli were separated by at least 10 sec. and repeated measures yielded no evidence of systematic changes in sensitivity. Stable individual differences in threshold and amplitude of response at threshold were found, but they were unrelated to differences in over-all emotion-ality (open-field test) or to differences in S''s startle response to acoustic signals. Analysis of response latencies suggested that flinch and jump reflect separate response mechanisms and that flinch is the primary behavioral manifestation of startle.