Cedrus

The present methodology allowed us to assess baseline acoustic startle as well as the acquisition, within-session extinction, and spontaneous recovery of fear-potentiated startle. The startle probe (noise burst) was a 108-dB [A], 40-ms burst of broadband noise with a near instantaneous rise time. The aversive stimulus (US) in these studies was a 250-ms airblast with an intensity of 140 psi directed to the larynx similar to that used in previously published methods (Jovanovic et al., 2005 (link); Norrholm et al., 2006 (link)). The airblasts were emitted by a compressed air tank connected to polyethylene tubing and controlled by a solenoid switch. The CSs were colored lights with color assignment counterbalanced across subjects.
For reinforced trials (A+ in both sets of experiments), a colored light was illuminated for a total of 4,995 ms. A startle probe (40 ms) was administered 4,000 ms after onset of the light. The airblast US (250 ms duration) was then presented 500 ms after the startle probe. The light terminated 205 ms after offset of the airblast. For nonreinforced trials (A− in the single-cue experiment or B− in the A+/B− experiment), the light was illuminated for a total of 4,245 ms. Again, a startle probe (40 ms) was administered 4,000 ms after onset of the light. The light terminated 205 ms after the startle probe. Startle probes were delivered on every trial as with previous human fear-potentiated startle studies (Ameli, Ip, & Grillon, 2001 (link); Grillon, Baas, Lissek, Smith, & Milstein, 2004 (link); Grillon, Dierker, & Merikangas, 1998 (link); Jovanovic et al., 2005 (link), Jovanovic et al., 2006 (link); Norrholm et al., 2006 (link)).
For both sets of experiments (single cue and differential conditioning, A+/B−), subjects participated in three separate sessions: CS habituation and acquisition (Session 1), extinction training (Session 2), and the extinction test (Session 3). Each startle session began with a 1-min acclimation period consisting of 70-dB broad-band noise, which continued throughout the session as background noise. Initial startle activity was reduced with 3 presentations of the 108-dB 40-ms startle probe without the CS, referred to as noise alone (NA) trials.
Subjects were randomly assigned to one of four experimental conditions: (a) single cue, immediate (10-min) extinction; (b) single cue, delayed (72-hr) extinction; (c) differential conditioning (A+/B−), immediate extinction, or (d) differential conditioning (A+/B−), delayed extinction. During the time period between acquisition and extinction training, subjects in the immediate group were taken out of the sound booth and placed in a quiet room adjacent to the startle testing room. EMG electrodes remained in place in between sessions.
A response keypad (SuperLab, Cedrus Corp.) was used in the startle sessions in coordination with the EMG startle response monitoring system (SR-LAB, San Diego Instruments) to collect trial-by-trial ratings of US expectancy. For each presentation of the CS, subjects indicated on the response keypad whether the light would be reinforced or nonreinforced, and this response was recorded for each light presentation. Subjects pressed a button marked “+” if they expected the CS to be followed by the US (danger), a button marked “+” if they did not expect the CS to be followed by the US (safety), and a button marked “0” if they did not know what to expect (uncertain). For the purposes of data analysis, subject responses of “+” were scored as 1, responses of “0” were scored as 0, and responses of “−” were scored as −1.