Fear-Potentiated Startle

The conditioned fear response (CR) constituted the eyeblink startle reflex potentiation to a loud noise through electromyography (EMG) of the right orbicularis oculi muscle. We administered the loud noise (40 ms; 104 dB) in the deliverance of each CS, as well as intertrial intervals [noise alone (NA)]. We conveyed all of the acoustic stimuli binaurally through earpieces (HD 600, Sennheiser, Germany). FPS was measured using Xeye Human Startle Reflex (Beijing Tianming Hongyuan Technology Development Co. Ltd., China). Two 4-mm Ag/AgCl electrodes full of the electrolyte gel were positioned about 1 cm beneath the pupil, as well as 1 cm under the lateral canthus, and a ground reference was positioned on the forehead (Blumenthal et al., 2005). The EMG electrodes were linked to an evoked potential amplifier set at an input resistance of 10 MΩ, as well as a bandwidth of DC-1500 Hz. To eliminate undesirable interferences, the notch filter was set at 50 Hz. The amplitude from the beginning to the peak (over the period of 50–300 ms after the probe onset) was assessed as the startle eye-blink magnitude (microvolts) and standardized for each subject via the T-normalization, yielding a distribution with a total mean of 50, along with a standard deviation of 10 for each stage. Startle response outliers were elucidated for each day separately (Z > 3) and were replaced by linear trend at points (Sevenster et al., 2012, 2013).