Article

Improving the acquisition of nociceptive evoked potentials without causing more pain

Kramer, John L.K.^a,*; Haefeli, Jenny^a,b; Jutzeler, Catherine R.^a,b; Steeves, John D.^c; Curt, Armin^a

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article

^aSpinal Cord Injury Center, University of Zurich, University Hospital Balgrist, Zurich, Switzerland

^bSwiss Federal Institute of Technology, Zurich, Switzerland

^cInternational Collaboration On Repair Discoveries, University of British Columbia, British Columbia, Vancouver, Canada

^*Corresponding author. Address: Spinal Cord Injury Center, University of Zurich, University Hospital Balgrist, Forchstrasse 340, CH 8008 Zurich, Switzerland. Fax: +41 44 386 3909.

E-mail: [email protected]

Submitted February 23, 2012; revised September 7, 2012; accepted October 18, 2012.

Pain 154(2):p 235-241, February 2013. | DOI: 10.1016/j.pain.2012.10.027

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Abstract

Summary

Causing a greater subjective pain experience is not necessary for improving the objective assessment of pain using contact heat-evoked potentials.

Following nociceptive heat or laser stimulation, an early contralateral and later vertex potential can be recorded. Although more indicative of the nociceptive input, the acquisition of the contralateral N1 after contact heat stimulation (contact heat-evoked potentials [CHEPs]) remains difficult. An advantage of contact heat is that the baseline skin temperature preceding peak stimulation can be controlled. Increasing the baseline temperature may represent a novel strategy to improve the acquisition of CHEPs without resulting in more subjective pain to stimulation. A study was undertaken in 23 healthy subjects to examine the effects of increasing the baseline temperature but not the perceived intensity of contact heat stimulation. A combined standard averaging and single-trial analysis was performed to disclose how changes in averaged waveforms related to latency jitter and individual trial amplitudes. By increasing the baseline temperature, the acquisition of N1 was improved among subjects with a low-amplitude response (greater than −4 μV) following 35°C baseline temperature stimulation (P < .05). Based on standard averaging, N2/P2 amplitudes were also significantly increased with and without an accompanying change in the rating of perceived pain when the baseline temperature was increased (P < .05). In contrast, automated single-trial averaging revealed no significant difference in N2 amplitude when the baseline temperature was increased to 42°C and the peak temperature reduced. These findings suggest that 2 mechanisms underlie the improved acquisition of CHEPs: increased synchronization of afferent volley, yielding larger-amplitude evoked potentials in response to the same rating of intensity; and reduced inter-trial variability.