Neural electrophysiological features of laser-evoked potentials and their applications

Abstract

Pain is related to the encoding and processing of afferent nociceptive information in the brain, and is a critical factor that allows humans and animals to learn to avoid potential or actual tissue injury. Being conducted by Aδ fibers and C fibers, nociceptive signals are processed by multiple brain structures, and normally generate a double sensation: an initial pricking pain (first pain) and a prolonged burning sensation (second pain). Intense laser heat pulses can selectively excite nociceptive free nerve endings in superficial layers of the skin. Such stimuli can elicit changes in brain responses (laser-evoked potentials, LEPs) in the ongoing electroencephalograms (EEGs). Until now, six reliable components have been detected in Aδ-LEPs: Aδ-N1, Aδ-N2, Aδ-P2, and Aδ-P4 waves in the time domain and alpha-band event-related desynchronization (α-ERD) and gamma-band event-related synchronization (γ-ERS) in the time- frequency domain. Meanwhile, by optimizing the experimental paradigm and parameters, two components of C-LEPs have been reliably detected: C-N2 and C-P2 waves in the time domain. The present paper reviewed the neural electrophysiological features of LEPs and their cognitive significance. LEPs can not only be used to investigate the peripheral and central processing of nociceptive sensory input, which is important in several clinical applications, but also be adopted in some basic research (e.g., the aging problem and social cognition) as a novel neurophysiological technique.