Temporal contrast enhancement in auditory and nociceptive processing

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 nonpainful but aversive sensory stimulation. In this study, healthy and pain-free participants were enrolled in 2 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 are consistent with 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.