Pain-Related Evoked Potentials

Laser-evoked brain potentials (LEPs) are brain responses elicited by the brief activation of heat-sensitive skin nociceptors and their spinothalamic projections. LEPs are currently the best-available clinical tool to assess spinothalamic function. An additional clinical tool for the assessment of small sensory nerve fiber function is offered by the contact heat evoked potential stimulator (CHEPS); it provides a clinically practical, noninvasive, and objective measure and can be a useful additional tool for the assessment of sensory small-fiber neuropathy. Another objective method for the evaluation of the nociceptive system is represented by the recording of pain-related evoked potentials (PREPs). The skin afferents are transcutaneously excited by a concentric electrode that produces a high current density at low current intensities. Therefore, the depolarization of nociceptive fibers is limited to the superficial layer of the dermis and does not reach the deeper layers that predominantly excite Aβ fibers. All these neurophysiological techniques cause nociceptive stimulations which are registered by the scalp in the form of EEG. It is possible to improve the study of the nociceptive system by looking at other EEG features induced by noxious stimuli. Actually, most EEG studies examining pain processing using laser stimuli have examined the components of laser-evoked potential (LEP). Knowledge of pain processing mechanisms can be improved with new methods that can detect subtle changes in EEG rhythms through painful stimulation. Brain network analysis may give an aid in understanding subtle changes of pain processing under laser stimuli in patients with neuropathic pain. The study of the dynamical relationships between signals recorded at different scalp locations can help to confirm and formulate hypotheses on the physiological mechanisms related to stimuli processing.