Mp100 data acquisition module

Mild electric shocks (200ms) were delivered through a bar electrode (Biopac Systems) attached with a Velcro strap to participants’ wrist. Bar electrode wells were manually filled with NaCl electrolyte gel to enhance conductance and attached to a SD9 Square Pulse Stimulator (Grass Technologies). To identify each individual’s shock level, mild shocks were manually triggered and increased in increments of 5V until the participant reported the shock to be uncomfortable, but not painful, or 60V were reached. To record SCR, shielded Ag-AgCl electrodes filled with standard NaCl electrolyte gel were applied to participant’s left index and middle fingers. SCR was sampled at a rate of 200Hz and recorded using an MP100 Data Acquisition module (BIOPAC Systems) connected to an Apple computer.

Salivary samples were collected to assess cortisol concentrations, via swab placed under the tongue for 2 min. Swabs were kept in cold storage at −10°C until sent to Salimetrics Laboratory for duplicate biochemical assay analysis. To assess cortisol change across time, we calculated the area under the curve with respect to increases from baseline (AUC_I) for each participant using the trapezoidal method.
To assess sympathetic nervous system arousal, we measured skin conductance via electrodes placed on the participant’s fingers, sampled at 200 Hz using an MP100 Data Acquisition Module (Biopac Systems). During the 2 min SECPT/control procedure, skin conductance levels (SCL) were measured as the mean tonic activity. During the memory task, skin conductance responses (SCR) were assessed via the sum of trough-to-peak waveform amplitude responses (in microsiemens, µS) across all trials (0.5s to 14.5s window; square-root transformed). Responses lower than 0.02 µS were recorded as zero. Data were preprocessed by low-pass filtering (25 Hz cut-off) and mean-value smoothing using a three-sample window.