The relation of skin conductance and pupillary fluctuations assessed by phase-rectified signal averaging

The reaction of pupil diameter and skin conductance are widely studied marker of the autonomic response to arousing stimuli. However, little is known about their relation at rest. In this study, we used bivariate phase-rectified signal averaging to investigate the relationship of skin conductance fluctuations (SCF) and pupillary fluctuations in 83 healthy volunteers. The onset of each SCF was detected by a pattern matching algorithm. Those time points were corrected for a different neurotransmission delay. Cross-correlation of temporal derivatives of pupil diameter and skin conductance revealed an average time lag of 2.5s. Thus, anchor points 2.5s before an SCF were defined. The pupillary signal following these anchors (7s) were extracted and normalized to baseline 1s prior to the anchor point. Aligned segments were averaged to determine the amplitude and area under the curve (AUC) of characteristic pupil diameter fluctuations (PDF) concurrent to SCF. The same procedure was applied to random time points (non-SCF) with at least 1s distance to actually detected SCF which served as control condition. SCF were accompanied by increases of pupil diameter with a maximum dilation of 9% on average. The one sample t-test indicated an AUC of PDF (70 ± 110 n.u., p<; 0.001). The maximum change and AUC of pupillary reactions were significantly higher when PDF extraction was triggered by actual SCF (both p<; 0.001). Both measures of pupillary dilations contributed significantly to pupillary unrest. Our results suggest that sympathetic arousal as detected by skin conductance fluctuations is accompanied by pupil dilation.