Responses of the supra-sylvian (SII) cortex in humans to painful and innocuous stimuli

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Abstract
In this study we compare the intrinsic characteristics and localization of nociceptive CO2 laser evoked potential (LEP) and non-nociceptive electrical EP (SEP) sources recorded by deep electrodes (one to two electrodes per patient, 10–15 contacts per electrode) directly implanted in the supra-sylvian cortex of 15 epileptic patients. Early CO2 laser (N140–P170) and electrical (N60–P90) evoked potentials were recorded by all of the electrodes implanted in the supra-sylvian cortex contralateral to stimulation. SEPs and LEPs had similar waveforms and inter-peak latencies. The LEPs appeared 84±15 ms later and were, on average, 14.2±22.2 μV smaller than the SEPs. These differences may be accounted for by the characteristics and the sizes of the different peripheral fibers (Aδ vs. Aβ) activated by the two types of stimuli. The stereotactic Talairach coordinates of the SEP and LEP sources covered the pre- and post-rolandic upper bank of the sylvian fissure, and were not significantly different for noxious and non-noxious stimuli. The spatial distribution of these contralateral responses fits with that of the modeled sources of scalp CO2 LEPs, magneto-encephalographic studies, and PET data from pain and vibrotactile activation studies. These results permit us to define the SII cortex as a cortical integration area of non-nociceptive and nociceptive inputs. This is supported by: (i) anatomical data reporting that the SII area receives inputs from both posterior columns and spino-thalamic pathways conveying the non-noxious and noxious information, respectively, and (ii) single cell recordings in monkeys, demonstrating that the SII area contains both nociceptive-specific neurons and wide-dynamic-range neurons receiving convergent input from nociceptive and non-nociceptive somatosensory afferents.