Abstract
Top-down attention towards nociceptive stimuli can be modulated by asking participants to pay attention to specific features of a stimulus, or to provide a rating about its intensity/unpleasantness. Whether and how these different top-down processes may lead to different modulations of the cortical response to nociceptive stimuli remains an open question. We recorded electroencephalographic (EEG) responses to brief nociceptive laser stimuli in 24 healthy participants while they performed a task in which they had to compare two subsequent stimuli on their Spatial location (Location task) or Intensity (Intensity Task). In two additional blocks (Location + Ratings, and Intensity + Ratings) participants had to further provide a rating of the perceived intensity of the stimulus. Such a design allowed us to investigate whether focusing on spatial or intensity features of a nociceptive stimulus and rating its intensity would exert different effects on the EEG responses. We did not find statistical evidence for an effect on the signal while participants were focusing on different features of the signal. We only observed a significant cluster difference in frontoparietal leads at approximately 300–500 ms post-stimulus between the magnitude of the signal in the Intensity and Intensity + Rating conditions, with a less negative response in the Intensity + Rating condition in frontal electrodes, and a less positive amplitude in parietal leads. We speculatively propose that activity in those electrodes and time window reflects magnitude estimation processes. Moreover, the smaller frontal amplitude in the Intensity + Rating condition can be explained by greater working memory engagement known to reduce the magnitude of the EEG signal. We conclude that different top-down attentional processes modulate responses to nociceptive laser stimuli at different electrodes and time windows depending on the underlying processes that are engaged.
Highlights
Attention can increase or decrease the magnitude of the cortical responses elicited by nociceptive stimuli depending on the processes that are involved
No significant difference was observed for the perceived intensity (t(23) = −0.664 p = 0.513) between the Intensity + Rating (IR) and Location + Rating (LR) conditions
This study was designed to investigate whether different top-down attentional processes led to different modulations of the cortical response to nociceptive stimuli
Summary
Attention can increase or decrease the magnitude of the cortical responses elicited by nociceptive stimuli depending on the processes that are involved (for reviews see Legrain et al, 2012; Torta et al, 2017). Top-down attention towards nociceptive stimuli can be incremented by asking participants to pay attention to specific features of a stimulus, or to provide a rating about its intensity and/or its unpleasantness Whether these different top-down processes lead to different modulations of the cortical response to nociceptive stimuli remains an open question. By contrasting the cortical activity during the two tasks, they showed that areas of the right posterior parietal cortex exhibited stronger and more sustained activity during the condition wherein participants were tracking spatial changes. Attention to both spatial and intensity features was associated with the activation of frontoparietal regions and the primary somatosensory cortex (S1), with a greater activation of the left dorsolateral prefrontal cortex (DLPFC) in the intensity discrimination task. The first aim of this study was to investigate whether focusing on changes in the location vs. the intensity of the laser stimuli could modulate cortical activity in other post-stimulus intervals
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