A comparison between the neural correlates of laser and electric pain stimulation and their modulation by expectation

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Hird, EJ 
Jones, AKP 

Abstract Background Pain is modulated by expectation. Event-related potential (ERP) studies of the influence of expectation on pain typically utilise laser heat stimulation to provide a controllable nociceptive-specific stimulus. Short painful electric stimulation has a number of practical advantages, but is less nociceptive-specific. We compared the modulation of electric versus laser-evoked pain by expectation, and their corresponding pain-evoked and anticipatory ERPs. New Method We developed understanding of recognised methods of laser and electric stimulation. We tested whether pain perception and neural activity induced by electric stimulation was modulated by expectation, whether this expectation elicited anticipatory neural correlates, and how these measures compared to those associated with laser stimulation. We elicited cue-evoked expectations of high and low pain and compared subjective ratings and corresponding ERPs in response to the delivery of laser and electric stimulation in a within-participant design. Results Despite sensory and affective differences between laser and electric pain, intensity ratings and pain-evoked potentials were modulated equivalently by expectation, though ERPs only correlated with pain ratings in the laser pain condition. Anticipatory correlates significantly differentiated pain intensity expectation to laser but not electric pain. Comparison with Existing Method Previous studies have consistently shown that laser-evoked potentials are modulated by expectation. We extend this by showing electric pain-evoked potentials are equally modulated by expectation, within the same participants. We also show a difference between the pain types in anticipation. Conclusions Though laser-evoked potentials express a stronger relationship with pain perception, both laser and electric stimulation may be used to study the modulation of pain-evoked potentials by expectation. Anticipatory-evoked potentials are elicited by both pain types, but they may reflect different processes and did not correlate with pain perception.

32 Biomedical and Clinical Sciences, 3209 Neurosciences, 3202 Clinical Sciences, Neurosciences, Chronic Pain, Pain Research, Clinical Research
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Journal of Neuroscience Methods
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This work was supported by a studentship grant from the Medical Research Council, UK. We would like to acknowledge the Medical Physics team at Salford Royal Foundation Trust, especially P. Samraj and S. Watson, for their technical assistance in building the Labview program to operate the laser. We thank T. Rainey for his technical expertise and assistance. WeD acknowledges the support of CONICYT, Chile, Basal project FB0008 and FONDECYT project 1161378.