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

Abstract

related potentials (ERPs) elicited by transient nociceptive stimuli in humans are largely sensitive to bottom-up novelty induced, for example, by changes in stimulus attributes (e.g., modality or spatial location) within a stream of repeated stimuli. Here we aimed 1) to test the contribution of a selective change of the intensity of a repeated stimulus in determining the magnitude of nociceptive ERPs, and 2) to dissect the effect of this change of intensity in terms of "novelty" and "saliency" (an increase of stimulus intensity is more salient than a decrease of stimulus intensity). Nociceptive ERPs were elicited by trains of three consecutive laser stimuli (S1-S2-S3) delivered to the hand dorsum at a constant 1-s interstimulus interval. Three, equally spaced intensities were used: low (L), medium (M), and high (H). While the intensities of S1 and S2 were always identical (L, M, or H), the intensity of S3 was either identical (e.g., HHH) or different (e.g., MMH) from the intensity of S1 and S2. Introducing a selective change in stimulus intensity elicited significantly larger N1 and N2 waves of the S3-ERP but only when the change consisted in an increase in stimulus intensity. This observation indicates that nociceptive ERPs do not simply reflect processes involved in the detection of novelty but, instead, are mainly determined by stimulus saliency. habituation; pain; electroencephalography; stimulus intensity BRIEF INFRARED LASER HEAT pulses selectively activate A␦ and C fiber skin nociceptors in the superficial skin layers (Bromm and Treede 1984). Such stimuli elicit transient event-related potentials [laser-evoked potentials (LEPs)], related to the activation of A␦ nociceptors. 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).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. Indeed, similar brain responses can be elicited by nonnociceptive sensory stimuli that are never perceived as painful, provided that they are salient (Legrain et al. 2011;Mouraux and Iannetti 2009). Furthermore, the well-known positive correlation between the intensity of perceived pain and the magnitude of LEPs can be disrupted in several experimental conditions, such as stimulus repetition at a short and constant interval Treede et al. 2003;Wang et al. 2010).Finally, there is a large amount of evidence that the main LEP waves can be modu...

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“…Other authors have described similar ideas in the literature of Stop Tasks with reward contingencies, using other terms such as the “Arousal Effect” (Shanahan et al, 2008) or the “Novelty effect” (Ronga et al, 2013). The concepts are not equivalent since the effects where not alike.…”

Role of explicit verbal information in conditioned analgesia

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