Neural dynamics during heat pain threshold assessment using the method of limits

Area of Science:

• Neuroscience
• Pain Research
• Sensory Physiology

Background:

• Quantitative sensory testing (QST) using heat pain threshold (HPT) is common in research and clinical settings.
• Direct investigation of neuronal responses during HPT assessment is limited.
• Understanding brain activity during HPT is crucial for pain research.

Purpose of the Study:

• To investigate brain BOLD (Blood-Oxygen-Level-Dependent) responses during HPT assessment using the Method of Limits (MoL).
• To characterize the stimulus-response (SR) patterns in various brain regions.
• To assess the predictive power of the Neurological Pain Signature (NPS) and Hidden Markov Models (HMM) for HPT.

Main Methods:

• Functional magnetic resonance imaging (fMRI) to measure BOLD signals in 30 healthy males.
• Ascending thermal ramps using the MoL for HPT determination.
• Analysis of peristimulus BOLD time courses and application of HMM.

Main Results:

• Rostro-dorsal anterior insula (aINS) showed linear SR behavior with stimulus intensity.
• Anterior midcingulate cortex (aMCC), primary somatosensory cortex (SI), and ventral aINS exhibited sudden signal increases above HPT.
• NPS predicted HPT at group and individual levels, with subregions overlapping linear SR areas.
• HMM reliably predicted individual MoL-derived HPT.

Conclusions:

• Brain responses to heat pain are region-specific, with some areas showing intensity-dependent linear patterns and others threshold-dependent activation.
• The NPS may be influenced by stimulus intensity, not solely by pain detection.
• HMM provides a robust method for predicting individual HPT and understanding brain dynamics during the heat-to-pain transition.