Association between respiratory sinus arrhythmia and reductions in startle responding in three independent samples

• Respiratory sinus arrhythmia (RSA) is an index of physiological flexibility.
• Examined whether RSA was associated with decreases in startle responding over time.
• In two samples, low RSA was associated with less of a reduction in responding.
• When contextual anxiety was removed in a third sample, this relation was not found.
• RSA is selectively associated with habituation within the context of anxiety.

Evidence suggests that respiratory sinus arrhythmia (RSA) may be an important indicator of physiological flexibility. However, few studies have examined the relation between RSA and defensive habituation, a process contingent on physiological flexibility. In three independent samples, habituation was defined as the time course of 9 startle responses. In Sample one and two, startle was recorded (1) while shock electrodes were attached to participants’ and (2) before a threat-of-shock task. In Sample three, startle was recorded without these two components. In the first two samples, startle magnitude significantly decreased over time but in Sample three, startle only decreased at a trend level. Further, low RSA was associated with less of a reduction in startle magnitude over time within the first two samples, but was unrelated to startle reduction in the third. This suggests that low RSA is associated with less habituation to contextual anxiety, which may reflect difficulties regulating anxiety.