Physiological Measures in fMRI Experiment

Heart rate and respiration were successfully recorded during the fMRI experiment from 12 participants using the BIOPAC MP150 Data Acquisition System (BIOPAC System, Inc.). Heart rate was measured using BIOPAC TSD200 pulse plethysmogram transducer, which records the blood volume pulse waveform optically. The pulse transducer was placed on the palmar surface of the participant's left index finger. Respiratory movements were measured using BIOPAC TSD201 respiratory-effort transducer attached to an elastic respiratory belt, which was placed around each participant's chest to measure changes in thoracic expansion and contraction during breathing. Both signals were sampled simultaneously at 1 kHz using RSP100C and PPG100C amplifiers for respiration and heart rate, respectively, and BIOPAC AcqKnowledge software (version 4.1.1). Respiration and heart signals were then down-sampled to 10 Hz to extract just the time-varying heart and respiration rates (cycles per minute) with the DRIFTER toolbox (Sarkka et al., 2012 (link)) after the effects of movement (i.e., spiky signals) were smoothed, when necessary, by interpolating. Finally, mean heart and breathing rates were computed and down-sampled to 5 Hz to match the valence and arousal self-report time series (see below), and correlations were computed between valence, arousal, and heart and breathing rates.