Somatosensory spatial attention modulates amplitudes, latencies, and latency jitter of laser-evoked brain potentials

Abstract

Several studies provided evidence that the amplitudes of laser-evoked potentials (LEPs) are modulated by attention. However, previous reports were based on across-trial averaging of LEP responses at the expense of losing information about intertrial variability related to attentional modulation. The aim of this study was to investigate the effects of somatosensory spatial attention on single-trial parameters (i.e., amplitudes, latencies, and latency jitter) of LEP components (N2 and P2). Twelve subjects participated in a sustained spatial attention paradigm while noxious laser stimuli (left hand) and noxious electrical stimuli (right hand) were sequentially delivered to the dorsum of the respective hand with nonnoxious air puffs randomly interspersed within the sequence of noxious stimuli. Participants were instructed to mentally count all stimuli (i.e., noxious and nonnoxious) applied to the attended location. Laser stimuli, presented to the attended hand (ALS), elicited larger single-trial amplitudes of the N2 component compared with unattended laser stimuli (ULS). In contrast, single-trial amplitudes of the P2 component were not significantly affected by spatial attention. Single-trial latencies of the N2 and P2 were significantly smaller for ALS vs. ULS. Additionally, the across-trial latency jitter of the N2 component was reduced for ALS. Conversely, the latency jitter of the P2 component was smaller for ULS compared with ALS. With the use of single-trial analysis, the study provided new insights into brain dynamics of LEPs related to spatial attention. Our results indicate that single-trial parameters of LEP components are differentially modulated by spatial attention.

Understanding the mechanisms through which spatial attention acts on nociception

“…This set is then applied to single trials and allows latency and amplitude to be determined for each ERP peak. This analysis has been suggested to offer a more accurate and unbiased estimation of ERPs latency and amplitude (Hu et al 2011).In their results, Franz et al (2015) observed that, irrespective of the method that was used (standard averaging or single-trial analysis), N2 peaks were larger in the attended condition. This would suggest that the effects of spatial attention on the magnitude of the N2 peak are not influenced by possible latency jitters occurring at the single-trial level.…”

“…Several studies have shown that attention is able to modulate behavioral and brain responses to noxious inputs (see Legrain et al 2012 for a review on event-related potentials, ERPs). However, attention is not a unitary construct; indeed, different attentional processes have been identified, and a systematic investigation of the physiological mechanisms through which these different processes can shape nociception remains elusive.In their recent article, Franz et al (2015) provide an interesting perspective on the mechanisms through which spatial attention (i.e., attention allocated to a specific spatial location) exerts its modulation on brain responses to nociceptive laser stimuli (i.e., laser-evoked potentials, LEPs). The authors aimed to investigate not only the effects of attention on the magnitude of the response but also the effects on the latency of the response, with a particular focus on the trial-to-trial variability.…”

“…Franz et al (2015) used "medium" perceived intensities. It would be interesting, in future studies, to investigate the effects of spatial attention on stimuli of different intensities, chosen both by physical properties (e.g., the intensity of the stimulus itself as in Legrain et al 2002Legrain et al , 2003 and by perceived intensity (as in Franz et al 2015).By showing that spatial attention has an effect on stimulus latency and latency jitter, Franz et al (2015) provide useful insights on how attention can fluctuate over trials, thereby influencing the chronometry of stimulus processing. Contrary to research in other sensory domains (i.e., vision) in which the relationship between spontaneous fluctuations of attention and perception has been addressed (Romei et al 2008), research in the pain field has long neglected this possibility.…”

“…In detail, the authors observed that attention to pain increased blood oxygen level-dependent (BOLD) levels in the insula, midcingulate cortex, primary and secondary somatosensory cortices (contralateral to the side of pain stimulation), and temporoparietal junction. Attention to pain was also associated with decreased BOLD levels in areas of the default mode network (DMN), including the posterior cingulate cortex and the medial prefrontal cortex.Some final observations could be put forward in relation to the study of Franz et al (2015). Laser stimuli were always presented on the left hand.…”

“…In their recent article, Franz et al (2015) provide an interesting perspective on the mechanisms through which spatial attention (i.e., attention allocated to a specific spatial location) exerts its modulation on brain responses to nociceptive laser stimuli (i.e., laser-evoked potentials, LEPs). The authors aimed to investigate not only the effects of attention on the magnitude of the response but also the effects on the latency of the response, with a particular focus on the trial-to-trial variability.…”