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

Area of Science:

• Neuroscience
• Pain Research
• Sensory Science

Background:

• Temporal summation of pain (TSP) is a key indicator of central pain facilitation.
• The reliability of TSP measurement can vary significantly based on the stimulation protocol used.

Purpose of the Study:

• To compare responder rates and magnitudes of TSP across various common protocols.
• To assess the within-person generalizability of TSP measurements.
• To identify the most reliable protocol for measuring TSP.

Main Methods:

• A within-subject design with 39 healthy adults completing five TSP protocols (laser, mechanical punctate, mechanical pressure, tonic heat, phasic heat).
• Pain was individually calibrated and rated on a 0-100 scale.
• Responder rates, TSP magnitudes, and laser induction rates were primary outcomes.

Main Results:

• Responder rates varied significantly across protocols, with laser stimulation showing 100% (39/39) and tonic heat only 10.2% (4/39).
• TSP magnitudes were highest for laser (24.1%) and decreased for tonic heat (-20.0%).
• Within-person consistency was low, with only 5.1% of participants showing stable TSP rankings across all protocols.

Conclusions:

• TSP expression is highly dependent on the chosen stimulation protocol.
• Nociceptor-dominant laser stimulation provides the most consistent and reliable method for evoking TSP.
• Laser-based TSP measurement is recommended for mechanistic and translational pain studies, including biomarker development.