Contactless laser elicits robust temporal summation compared with mechanical and contact‑heat protocols

Temporal summation of pain (TSP) indexes central pain facilitation, but its expression may depend on how noxious input is delivered. This study compared TSP responder rates and magnitudes across common protocols and assessed within-person generalizability. In a randomized, counterbalanced, within-subject design, 39 healthy adults completed five TSP protocols spanning three modalities: radiant-heat laser (contactless, triplets), mechanical punctate (10 pulses), mechanical pressure (10 pulses), and contact heat delivered as phasic (20 pulses) or tonic (60 s). Pain was individually calibrated and rated on a 0-100 scale. Primary outcomes were responder rate (TSP > 0) and TSP magnitude; for laser, an induction rate (proportion of triplets with S3 > S1) was also computed. Responder rates differed across protocols (Cochran's Q = 92.6, p < 0.0001): laser 100% (39/39), pressure 79.5% (31/39), punctate 66.7% (26/39), tonic 10.2% (4/39), and phasic 15.4% (6/39). TSP magnitudes also differed (Friedman, p < 0.0001), with the largest values for laser (median (IQR) 24.1% (27.4%)), intermediate for pressure (16.7% (23.0%)) and punctate (6.0% (20.0%)), and decreases for tonic (-20.0% (28.3%)) and phasic heat (-16.7% (31.3%)). For laser, the induction rate averaged 70% (16.7%) (range 30-97%). Within-person rankings were unstable across protocols, with only 5.1% of participants maintaining the same TSP group across all paradigms. In healthy adults, TSP is strongly protocol dependent; laser stimulation yields the most reliable facilitation, supporting its use in mechanistic and translational studies, including efforts to develop predictive biomarkers for neuromodulation response. PERSPECTIVE: Temporal summation of pain (TSP) is widely used to index central pain facilitation, yet its predictive value depends on how it is measured. This study shows that nociceptor-dominant laser paradigms evoke the most consistent TSP, supporting their use in mechanistic studies and biomarker development across pain research contexts.