Pain measurement with evoked potentials: combination of subjective ratings, randomized intensities, and long interstimulus intervals produces a P300-like confound

Evoked potentials in response to painful stimuli have been studied as objective measures of pain. Bromm has advocated experimental conditions in which, (1) stimulus intensities are randomized, and (2) subjects rate each stimulus. However, a cognitive, i.e. information processing, ‘late positive comp...

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Bibliographic Details
Published in:	Pain (Amsterdam) Vol. 84; no. 1; pp. 37 - 47
Main Authors:	Becker, David E., Haley, David W., Ureña, Vivian M., Yingling, Charles D.
Format:	Journal Article
Language:	English
Published:	Amsterdam Elsevier B.V 2000 Lippincott Williams & Wilkins, Inc Elsevier
Subjects:	Adult Biological and medical sciences Cognition Electric Stimulation Electroencephalography Event-Related Potentials, P300 - physiology Fingers - innervation Fundamental and applied biological sciences. Psychology Humans Late positive component Male P300 Pain Pain - physiopathology Pain evoked potential Pain Measurement - methods Pain Threshold Sensory Thresholds Somesthesis and somesthetic pathways (proprioception, exteroception, nociception); interoception; electrolocation. Sensory receptors Vertebrates: nervous system and sense organs Late positive component Pain evoked potential Pain P300 Human Nociception Noxious stimulus Topography Central nervous system Information processing Electrophysiology Stimulus intensity Event evoked potential Brain (vertebrata)
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Summary:	Evoked potentials in response to painful stimuli have been studied as objective measures of pain. Bromm has advocated experimental conditions in which, (1) stimulus intensities are randomized, and (2) subjects rate each stimulus. However, a cognitive, i.e. information processing, ‘late positive component’ (LPC), e.g. the P300, may be elicited by these same conditions, whether or not the stimuli are painful. The LPC may overlap, and interfere with the measurement of, responses that are only seen with painful stimuli. We compared the LPC in two experimental protocols using ten subjects and electrical stimuli. In the ‘Rating Protocol’, shocks of different intensity levels were randomly presented and subjects rated the intensity of each stimulus. In the ‘Oddball Standards Protocol’, the same levels were used, but each was presented in a separate block of a single level. Stimuli were presented more rapidly and subjects had to push a button in response to occasional double shocks (oddball targets), but not to single shocks (oddball standards). The oddball targets served to direct subjects’ attention to the stimuli, but only the evoked potential responses to the oddball standards were used for data analysis. To look at the difference between protocols, we computed a difference condition (Rating protocol responses minus Oddball Standards protocol responses) which we called Incremental activity. The Incremental LPC (average amplitudes from 350 to 650 ms) had a more parietal topography (amplitude at electrode Pz greater than at Cz) than the Oddball Standards LPC (Cz>Pz; protocol×electrode interaction P<0.001). This implies that the Rating Protocol LPC included P300-like activity. The parietal Incremental activity began as early as 250–350 ms after the stimulus in the responses to the most painful stimuli and therefore can confound the measurement of pain activity in the evoked potential.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0304-3959 1872-6623
DOI:	10.1016/S0304-3959(99)00182-7