To test this behavior in the mouse, they were placed in a small acrylic cylinder that was seated upon a piezoelectric transducer and located inside a larger sound attenuating chamber (San Diego Instruments SR Lab system). Each chamber contained a ceiling light, fan, and a loudspeaker for the acoustic stimuli (bursts of white noise) and was connected to a computer running SR Lab software which quantifies movement and vibrations during each trial. The test session consisted of 42 trials, presented following a 5-min habituation period, with 7 different types of trials: no-stimulus trials, trials with the acoustic startle stimulus (40ms; 120dB) alone, and trials in which a prepulse stimulus starting 4dB above background (20ms; 74, 78, 82, 86, 90dB) had onset 100ms before the onset of the startle stimulus. The different trial types were presented in blocks of 7, in randomized order within each block, with an average inter-trial interval of 15s (range: 10–20s). Measures were taken of the startle amplitude for each trial, defined as the peak response during a 65-ms sampling window that begins with the onset of the startle stimulus. Levels of percent prepulse inhibition were calculated as 100 − (prepulse response/startle response) × 100.
