Temporal contrast enhancement generalizes across pain and auditory modalities

Abstract

Temporal contrast enhancement (TCE), also termed offset analgesia, describes a temporal filtering mechanism whereby a small decrease in stimulus intensity produces a disproportionately large reduction in perceived pain. Although TCE is considered a robust marker of endogenous pain modulation, its underlying mechanisms remain unresolved. It is unclear whether TCE reflects a nociceptive-specific modulatory process or a supramodal temporal filtering mechanism that generalizes to non-painful but aversive sensory stimulation. In this study, healthy and pain-free participants were enrolled in two experiments: a behavioral study (n=33) or a neurophysiological study (n=29). Continuous pain-ratings, electroencephalography (EEG) and pupillometry data were collected. A conventional TCE paradigm was applied using either noxious heat delivered via a thermal contact stimulator or unpleasant auditory stimulation delivered through over-ear headphones. Both noxious heat and unpleasant sounds induced behavioral TCE-effects (p<0.01), indicating a supramodal mechanism with modality-specific temporal dynamics, which was further supported by the absence of a significant correlation of TCE-effects across modalities (p>0.05). In the second experiment, noxious heat - but not unpleasant sound - resulted in decreased power of neural alpha oscillations ([~]10 Hz, p<0.05) and increased pupil size (p<0.05) potentially indicating bottom-up modulation of the autonomic nervous system and a release of neural inhibition, respectively. However, subjectively experienced TCE-effects were not reflected in neurophysiological correlates. These findings support the view of TCE as a supramodal temporal filtering mechanism characterized by modality-specific temporal dynamics, for which no corresponding signatures are found in EEG or pupillometry.