Poehlmann, J. | bioRxiv Science

bioRxiv2025

Temporal contrast enhancement generalizes across pain and auditory modalities

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.

neuroscience↗

bioRxiv2025

Perception of first and second pain during offset analgesia

IntroductionOffset analgesia (OA) is defined as a disproportionate reduction in pain perception following a small decrease in noxious stimulation. However, the mechanisms underlying this phenomenon remain unclear, with ongoing debate on peripheral versus central contributions. ObjectivesThis experimental study aimed to differentiate first and second pain perception during the OA paradigm, thereby assessing fiber-specific influences on OA. MethodsThirty-two healthy participants were asked to distinguish a double pain sensation (first and second pain), to assess pain quality descriptors related to A-{delta} and C-fibers, and to indicate response times to brief noxious heat stimuli. This procedure was repeated while implementing heat pulses in an OA paradigm. ResultsNo significant differences were found between offset and constant trials in the reported double pain sensation or the fiber specific pain descriptors (p > 0.05). Nevertheless, significant differences in response times were observed depending on the type of trial and the timing of the stimulus. Response time to noxious stimuli was delayed after prolonged stimulation in both offset and constant trials (p < 0.05). ConclusionsThe findings suggest that A-{delta} and C-fiber response characteristics were unaffected during the OA paradigm; however, higher stimulation intensities or prolonged pain induce a notable response delay. This indicates a negligible role of specific peripheral nerve fibers in OA, emphasizing the predominance of central mechanisms, particularly those related to attention and cognitive resources, which merit further investigation.

neuroscience↗