Mp150 system

Prior to the conflict discussion, research assistants affixed two Ag-AgCl electrodes in a Lead II configuration to each member of the couple. During the discussion, cardiac activity was measured using an electrocardiogram (ECG) sampled at 1000 Hz using a BIOPAC MP150 system (BIOPAC Systems, Inc.; Goleta, California, USA). ECG data were converted to inter-beat intervals (IBI) using a peak detection algorithm implemented in the processHrv toolbox (Larry Greishar, University of Wisconsin) in MATLAB, then spline-interpolated onto a 10Hz grid to generate an evenly sampled time series reflecting heart rate variation. Trained research assistants identified and corrected missed and artifactual beats by visual inspection of the IBI series (supervised by AMS). Portions of time series where data were unreliable (e.g., due to premature ventricular contractions) were censored from analyses. Of the 220 participant recordings, we censored a small portion of the data for 15 participants: M = 3.9%, SD = 4.9%. Furthermore, given that low-frequency influences undermine estimation of momentary regulatory dynamics, we mean-centered and linearly detrended the IBI time series. Additional information about the technical specification of the ECG recording is provided in the Supplement.

Throughout the mpTSST, SCL, HR and facial EMG were continuously monitored using the Biopac MP150 system (Biopac Systems, Inc., Goleta, CA) with AcqKnowledge 4.1.5 data-acquisition software. Startle stimuli were timed and triggered using Superlab 4.5 (Cedrus Corp., San Pedro, CA) which simultaneously transmitted event marks allowing precise synchronization of each stimulus onset with the ongoing physiological recording. Previously published techniques were used for electrode placement (Pace-Schott et al., 2012b (link)) and processing responses to loud tones including SCR, orbicularis oculi blink EMG and HRA (Pace-Schott et al., 2014 (link)). Details of data reduction are provided in Supplementary Methods.

Surface electrocardiography (ECG) was performed on sedentary animals at 6 and 12 months of age as described previously [21 (link)]. Briefly, mice were placed on a warming pad in a supine position and maintained under anesthesia with 1.5% isoflurane in oxygen via nose cone. Three-lead ECG probes were inserted subcutaneously in which the positive, negative, and ground electrodes were placed in the left hindlimb, right forelimb, and left forelimb, respectively. The electrodes were linked to a biopotential amplifier (BIOPAC MEC100C) connected to a computer interfaced BIOPAC MP150 system (BIOPAC Systems Inc., Goleta, CA) to measure and record electrical signals. Traces for each animal were recorded continuously for 30 min. Heart rate measurements and R–R intervals were calculated using Acqknowledge software.