The Journal of Neuroscience, June 17, 2009, 29(24):7909-7916; doi:10.1523/JNEUROSCI.0014-09.2009
Previous Article | Next Article 
Behavioral/Systems/Cognitive
Characterizing the Cortical Activity through Which Pain Emerges from Nociception
Michael C. Lee,1,2 *
André Mouraux,3 * and
Gian Domenico Iannetti2
1Department of Anaesthesia, University of Cambridge, Cambridge CB2 2QQ, United Kingdom, 2Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, United Kingdom, and 3Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford OX3 9DU, United Kingdom
Correspondence should be addressed to Dr. Gian Domenico Iannetti, Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, UK. Email: giandomenico.iannetti{at}dpag.ox.ac.uk
Nociception begins when A
- and C-nociceptors are activated. However, the processing of nociceptive input by the cortex is required before pain can be consciously experienced from nociception. To characterize the cortical activity related to the emergence of this experience, we recorded, in humans, laser-evoked potentials elicited by physically identical nociceptive stimuli that were either perceived or unperceived. Infrared laser pulses, which selectively activate skin nociceptors, were delivered to the hand dorsum either as a pair of rapidly succeeding and spatially displaced stimuli (two-thirds of trials) or as a single stimulus (one-third of trials). After each trial, subjects reported whether one or two distinct painful pinprick sensations, associated with A-nociceptor activation, had been perceived. The psychophysical feedback after each pair of stimuli was used to adjust the interstimulus interval (ISI) of the subsequent pair: when a single percept was reported, ISI was increased by 40 ms; when two distinct percepts were reported, ISI was decreased by 40 ms. This adaptive algorithm ensured that the probability of perceiving the second stimulus of the pair tended toward 0.5. We found that the magnitude of the early-latency N1 wave was similar between perceived and unperceived stimuli, whereas the magnitudes of the later N2 and P2 waves were reduced when stimuli were unperceived. These findings suggest that the N1 wave represents an early stage of sensory processing related to the ascending nociceptive input, whereas the N2 and P2 waves represent a later stage of processing related, directly or indirectly, to the perceptual outcome of this nociceptive input.
Received Dec. 30, 2008;
revised May 1, 2009;
accepted May 9, 2009.
Correspondence should be addressed to Dr. Gian Domenico Iannetti, Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, UK. Email: giandomenico.iannetti{at}dpag.ox.ac.uk
