Non-phase locked electroencephalogram (EEG) responses to CO2 laser skin stimulations may reflect central interactions between A partial partial differential- and C-fibre afferent volleys.
OBJECTIVE
By co-activating A partial partial differential- and C-fibre nociceptors, intense CO2 laser heat stimuli produce a dual sensation, composed of first and second pain, but induce only a single A partial partial differential-fibre related late laser evoked potential (LEP). However, when avoiding concomitant activation of A partial partial differential-fibres, C-fibre related ultra-late LEPs are recorded. This poorly understood phenomenon was re-investigated using a method which, unlike time-domain averaging, reveals electroencephalogram (EEG) changes whether or not phase-locked to stimulus onset.


METHODS
CO2 laser stimuli were applied to the dorsum of the hand. Reaction-time was used to discriminate between A partial partial differential- and C-fibre mediated detections. Analyses were performed using a method based on the time-frequency wavelet transform of EEG epochs.


RESULTS
This study revealed: (1) a novel non-phase-locked component related to the activation of A partial partial differential-fibres occurring at similar latencies as the late LEP; and (2) a widespread post-stimulus event-related desynchronization (ERD) induced by both A partial partial differential- and C-fibres.


CONCLUSIONS
A partial partial differential- and C-fibre related LEPs could be electrophysiological correlates of similar brain processes, which, when already engaged by A partial partial differential-fibres, cannot or do not need to be reactivated by the later arriving C-fibre afferent volley. A partial partial differential-fibre related ERD could reflect a transient change of state of brain structures generating these responses.
Mouraux
A
A
Laboratoire de neurophysiologie (NEFY), Université catholique de Louvain, 54 Avenue Hippocrate, B-1200, Brussels, Belgium. andre.mouraux@nefy.ucl.ac.be <andre.mouraux@nefy.ucl.ac.be>
Guérit
J M
JM
Plaghki
L
L
D000328:Adult; D002245:Carbon Dioxide; D002540:Cerebral Cortex / Q000502:physiology; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D007834:Lasers; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology*; D010465:Perception / Q000502:physiology; D011930:Reaction Time / Q000502:physiology
D002245:Carbon Dioxide