The pain-related negative difference potential: a direct measure of central pain pathway activity or of interactions between the innocuous somatosensory and pain pathways?
Negative difference potential (NDP) is a sural nerve-evoked scalp potential derived by subtracting potentials elicited at the pain threshold level from those elicited at supra-pain threshold levels. Our recent work examined the possibility that the NDP reflects a pain-related inhibition of neurons in the innocuous somatosensory pathways. Although failing to find any evidence for this inhibition, these studies do present the possibility that the NDP reflects an attention- and/or task-related decrease in the innocuous somatosensory activity that is elicited by the noxious electrical stimulus. To test this hypothesis, 35 healthy subjects were given three attention/task relevance conditions presented in counterbalanced order: rate the subjective magnitude of the painful aspects of the noxious electrical stimulus; rate the subjective magnitude of the non-painful aspects of the noxious electrical stimulus; and, ignore the stimulus. Neither changes in attention nor the task relevance of the non-painful aspects of the stimulus had any effect on NDP amplitude. These data demonstrate that the NDP does not reflect an attention- or task-related modulation of innocuous somatosensory activity. Rather, our evidence to date suggests that the NDP is generated by activity in the central pain pathways.
Dowman
R
R
Department of Psychology, Clarkson University, Potsdam, New York 13699-5825, USA.
Schell
S
S
D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D001288:Attention / Q000502:physiology; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D017288:Pain Threshold / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D012018:Reflex / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology; D013497:Sural Nerve / Q000502:physiology