Heart talk: Emotional inner speech increases heart rate

In two pre-registered experiments (exp.1: n=44; exp.2: n=46), we investigated whether emotional inner speech influences heart rate. Participants were asked to engage in sessions of either: self-encouraging positive inner speech, self-degrading negative inner speech, or inner counting while their heart rate was monitored. Participants were lying on a bed and asked to remain still during the inner speech trials. Experiment 1 consisted of two negative, two positive and four counting trials. Experiment 2 had four trials of each type. Trials lasted 180 seconds in experiment 1 and had a mixed duration in experiment 2 (40-70 seconds) to limit predictability. Motion tracking was applied to control for body movement. Median heart rate across each inner speech session was analyzed and a significant difference was found between emotional inner speech and inner counting across both experiments. No difference between positive and negative inner speech was observed. Post-hoc analyses investigated the relationship between movement and heart rate increases and found an effect with a peak lag of approximately 14 seconds. Removing these effects did not change the effect that emotional inner speech had on heart rate. In line with previous literature, additional analyses showed that heart rate and respiration rate were linked. Including respiration rate as a variable in regression analyses did not alter the effect of emotion. The effect of emotional inner speech thus seems robust and demonstrates a causal effect on physiology. No correlations between heart rate effects and measures of depression and rumination were observed. We also discuss the results in relation to possible confounds, such as differences in cognitive effort and inner speech rate.