Divergent effects of conditioned pain modulation on subjective pain and nociceptive-related brain activity.
BACKGROUND AND OBJECTIVES
Pain is a complex experience involving both nociceptive and affective-cognitive mechanisms. The present study evaluated whether modulation of pain perception, employing a conditioned pain modulation (CPM) paradigm, is paralleled by changes in contact heat-evoked potentials (CHEPs), a brain response to nociceptive stimuli.


METHODS
Participants were 25 healthy, pain-free, college students (12 males, 13 females, mean age 19.24 ± 0.97 years). Twenty computer-controlled heat stimuli were delivered to the non-dominant forearm and CHEPs were recorded at Cz using a 32-channel EEG system. After each stimulus, participants rated the intensity of the heat pain using the 0-100 numerical rating scale. The latency and amplitude of N2, P2 components as well as single-sweep spectral analysis of individual CHEPs were measured offline. For CPM, participants had to submerge their dominant foot into a neutral (32 °C) or noxious (0 °C) water bath. CHEPs and heat pain ratings were recorded in 3 different conditions: without CPM, after neutral CPM (32 °C) and after noxious CPM (0 °C).


RESULTS
The noxious CPM induced a facilitatory pain response (p = 0.001) with an increase in heat pain following noxious CPM compared to neutral CPM (p = 0.001) and no CPM (p = 0.001). Changes in CHEPs did not differ between conditions when measured as N2-P2 peak-to-peak amplitude (p = 0.33) but the CPM significantly suppressed the CHEPs-related delta power (p = 0.03). Changes in heat pain in the noxious CPM were predicted by trait catastrophizing variables (p = 0.04).


CONCLUSION
The current study revealed that pain facilitatory CPM is related to suppression of CHEPs delta power which could be related to dissociation between brain responses to noxious heat and pain perception.
['Albu|Sergiu|S|http://orcid.org/0000-0001-8310-4208', 'Meagher|Mary W|MW|']
D001921:Brain D058443:Catastrophization D004569:Electroencephalography D005260:Female D006358:Hot Temperature D006801:Humans D008297:Male D009413:Nerve Fibers, Myelinated D010146:Pain D010147:Pain Measurement D058748:Pain Perception D017288:Pain Threshold D055815:Young Adult
Conditioned pain modulation Contact heat-evoked potentials Single-sweep spectral analysis Delta EEG activity Pain facilitation Pain inhibition