ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

4aAB1. The physiology and psychophysics of the acoustic startle reaction.

James R. Ison

Dept. of Brain and Cognitive Sci., Meliora Hall, Univ. of Rochester, Rochester, NY 14627

Intense noise bursts elicit in many animals, including humans, an abrupt and graded contraction of the flexor muscles called the ``acoustic startle reflex'' (ASR). Response vigor is determined in part by the acoustic properties of the eliciting stimulus, and in part by organismic factors such as biological rhythms, habituation, and emotion. Additionally it is powerfully affected by diverse and apparently irrelevant momentary shifts in the stimulus surround occurring just prior to the eliciting stimuli. These stimuli, called ``prepulses,'' can variously inhibit (``PPI'') or facilitate (``PPF'') the ASR, the general effect being ``reflex modification.'' The major variables affecting the strength of RM are prepulse salience and lead time, and, for short lead times, whether prepulses are increments or decrements in background level. Reflex modification has obvious intrinsic interest, and is being used to study sensory, perceptual, and cognitive processes in laboratory animals and in humans. The short brain-stem pathway responsible for ASR elicitation is simple and reasonably understood, with few remaining unknowns. In contrast, reflex modification consists of a set of less well understood semi-independent phenomena, which may variously call on different levels of the neuraxis, from brain stem to cortex, in processing stimulus input. [Work supported by NIH.]