Combined Evaluation of Nociceptive Detection Thresholds and Evoked Potentials during Conditioned Pain Modulation: A Feasibility Study

Abstract

Deficient top-down inhibitory control via diffuse noxious inhibitory control (DNIC) is a mechanism known to be responsible for the maintenance and development in several chronic pain syndromes. Experimentally, DNIC is often induced by conditioned pain modulation (CPM) paradigms such as a Cold Pressor Test (CPT). Recently, a method called the NDT-EP method has been developed with the aim to evaluate the nociceptive function, which it does via simultaneous tracking of nociceptive detection thresholds (NDT) and evoked potentials (EP). It remains to be investigated whether we can evaluate DNIC via the NDT-EP method. In this study, we take the first step to investigate this by evaluating the feasibility to combine the NDT-EP method with a 7 minutes CPT. In total 20 participants of a wide age-range were measured before, during, and after a CPT. All except 1 participant were able to complete the protocol, and enough stimulus-response pairs could be obtained for psychophysical as well as electrophysiological evaluation. Preliminary analysis of the NDT's and EP's showed results in line with earlier research such as a higher threshold for nociceptive stimuli and a lower EP amplitudes. Several NDT's of mostly elderly people (59±16 years), however, exceeded the maximum applicable stimulus strength during (7/20) or after (9/20) CPT and consequently had to be excluded from the analysis. To what extent this is a consequence of the CPT or other factors such as strong habituation associated more with elderly people, is subject to further investigation. In conclusion, the results of this study show that with the present protocol, it is feasible to combine the NDT-EP method with a CPM paradigm in almost all subjects, but that the NDT data of mostly older subjects could not be properly analyzed. Further directions for research and improvements are outlined.