The primary somatosensory cortex largely contributes to the early part of the cortical response elicited by nociceptive stimuli

Abstract

Research on the cortical sources of nociceptive laser-evoked brain potentials (LEPs) began almost two decades ago (Tarkka and Treede, 1993). Whereas there is a large consensus on the sources of the late part of the LEP waveform (N2 and P2 waves), the relative contribution of the primary somatosensory cortex (S1) to the early part of the LEP waveform (N1 wave) is still debated. To address this issue we recorded LEPs elicited by the stimulation of four limbs in a large population (n = 35). Early LEP generators were estimated both at single-subject and group level, using three different approaches: distributed source analysis, dipolar source modeling, and probabilistic independent component analysis (ICA).We show that the scalp distribution of the earliest LEP response to hand stimulation was maximal over the central-parietal electrodes contralateral to the stimulated side, while that of the earliest LEP response to foot stimulation was maximal over the central-parietal midline electrodes. Crucially, all three approaches indicated hand and foot S1 areas as generators of the earliest LEP response. Altogether, these findings indicate that the earliest part of the scalp response elicited by a selective nociceptive stimulus is largely explained by activity in the contralateral S1, with negligible contribution from the secondary somatosensory cortex (S2). © 2011 Elsevier Inc

Gamma-Band Oscillations in the Primary Somatosensory Cortex—A Direct and Obligatory Correlate of Subjective Pain Intensity

“…Together with the results of other recent studies (e.g., Valentini et al, 2012), this indicates a central role of SI in the processing of nociceptive stimuli. Most interestingly, the fact that GBOs constitute the only laser-induced EEG response which predicts the amount of perceived pain regardless of the saliency content of the stimulus, indicates that these neural activities originating from SI contribute directly to the emergence of a painful percept in response to nociceptive input.…”

Differences in cortical coding of heat evoked pain beyond the perceived intensity: An fMRI and EEG study

“…While these studies support that nociceptive stimuli are somatotopically organized in S1 (i.e., hand activation contralateral to the stimulation and foot activation close to the midline [Valentini et al, 2012]), evidence of somatotopic organization in S2 is less clear. One factor which may account for discrepancies regarding somatotopy in S2 is that a variety of region of interests have been applied across different studies [Bingel et al, 2004;Brooks et al, 2005;Ferretti et al, 2004;Ogino et al, 2005;Xu et al, 1997].…”

Novelty is not enough: laser-evoked potentials are determined by stimulus saliency, not absolute novelty

“…The largest LEP wave is a negative-positive complex maximal at the scalp vertex (N2-P2). This complex is preceded by a smaller negative wave (N1) maximal over the central-temporal region contralateral to the stimulated hand (Bromm and Treede 1984;Hu et al 2010;Valentini et al 2012). These waves reflect a combination of cortical activities originating from primary and secondary somatosensory cortices, the insula, and the anterior cingulate cortex (Garcia-Larrea et al 2003;Valentini et al 2012).…”

“…This complex is preceded by a smaller negative wave (N1) maximal over the central-temporal region contralateral to the stimulated hand (Bromm and Treede 1984;Hu et al 2010;Valentini et al 2012). These waves reflect a combination of cortical activities originating from primary and secondary somatosensory cortices, the insula, and the anterior cingulate cortex (Garcia-Larrea et al 2003;Valentini et al 2012).Although widely used to investigate the function of nociceptive pathways in health and disease (Haanpaa et al 2011), the physiological meaning of LEPs is still debated. Indeed, recent experimental evidence indicates that LEPs may reflect stimulus-triggered brain processes largely unspecific for nociception.…”