Timing of the Acoustic Startle Response in Mice: Habituation and Dishabituation as a Function of the Interstimulus Interval

The hypothesis that the standard acoustic startle response (ASR) paradigm contains the elements of interval timing was tested. Acoustic startle stimuli were presented at a 10-s interstimulus interval (ISI) for 100 trials leading to habituation of the ASR. The ISI was then changed to either a shorter (5-s) or a longer (15-s) duration using a betweensubjects design. Dishabituation of the ASR was used to measure the degree of temporal generalization for the interval-timing process. The ASR showed dishabituation at both shorter and longer ISI values on the first trial following the change in ISI. The dishabituation resulting from the change in ISI was temporary and the ASR rapidly returned to levels of response habituation showing rate sensitivity to the frequency of stimulus presentation. Interval timing may be a standard feature of this habituation paradigm, it serves to anticipate the time of occurrence of the subsequent stimulus and to prepare the startle response, and provides a computational dimension lacking in the habituation process per se.