Controlling attention to nociceptive stimuli with working memory

Background: Because pain often signals the occurrence of potential tissue damage, a nociceptive stimulus has the capacity to involuntarily capture attention and take priority over other sensory inputs. Whether distraction by nociception actually occurs may depend upon the cognitive characteristics of the ongoing activities. The present study tested the role of working memory in controlling the attentional capture by nociception. Methodology and Principal Findings: Participants performed visual discrimination and matching tasks in which visual targets were shortly preceded by a tactile distracter. The two tasks were chosen because of the different effects the involvement of working memory produces on performance, in order to dissociate the specific role of working memory in the control of attention from the effect of general resource demands. Occasionally (i.e. 17% of the trials), tactile distracters were replaced by a novel nociceptive stimulus in order to distract participants from the visual tasks. Indeed, in the control conditions (no working memory), reaction times to visual targets were increased when the target was preceded by a novel nociceptive distracter as compared to the target preceded by a frequent tactile distracter, suggesting attentional capture by the novel nociceptive stimulus. However, when the task required an active rehearsal of the visual target in working memory, the novel nociceptive stimulus no longer induced a lengthening of reaction times to visual targets, indicating a reduction of the distraction produced by the novel nociceptive stimulus. This effect was independent of the overall task demands. Conclusion and Significance: Loading working memory with pain-unrelated information may reduce the ability of nociceptive input to involuntarily capture attention, and shields cognitive processing from nociceptive distraction. An efficient control of attention over pain is best guaranteed by the ability to maintain active goal priorities during achievement of cognitive activities and to keep pain-related information out of task settings

The pain matrix reloaded: a salience detection system for the body

Neuroimaging and neurophysiological studies have shown that nociceptive stimuli elia salience detection system for the bodycit responses in an extensive cortical network including somatosensory, insular and cingulate areas, as well as frontal and parietal areas. This network, often referred to as the "pain matrix", is viewed as representing the activity by which the intensity and unpleasantness of the perception elicited by a nociceptive stimulus are represented. However, recent experiments have reported (i) that pain intensity can be dissociated from the magnitude of responses in the "pain matrix", (ii) that the responses in the "pain matrix" are strongly influenced by the context within which the nociceptive stimuli appear, and (iii) that non-nociceptive stimuli can elicit cortical responses with a spatial configuration similar to that of the "pain matrix". For these reasons, we propose an alternative view of the functional significance of this cortical network, in which it reflects a system involved in detecting, orienting attention towards, and reacting to the occurrence of salient sensory events. This cortical network might represent a basic mechanism through which significant events for the body's integrity are detected, regardless of the sensory channel through which these events are conveyed. This function would involve the construction of a multimodal cortical representation of the body and nearby space. Under the assumption that this network acts as a defensive system signaling potentially damaging threats for the body, emphasis is no longer on the quality of the sensation elicited by noxious stimuli but on the action prompted by the occurrence of potential threats

When Inequality is Equitable: Validity, Propriety and Third Party Allocations

The author summarizes theories of equity and distributive justice that predict actors use legitimate distribution rules to act to maintain or to restore equity. He elaborates those ideas, distinguishing legitimacy based on validity (socially supported) from propriety (acceptance by the focal actor). Experimental research showed strong effects of both types of legitimacy on behavior, with validity having slightly stronger effects.This research was supported by a grant from the National Science Foundation (SOC #7817^3<»), Morris Zelditch, Jr.» Principal Investigator. Computations were supported by a grant from the Office of the Dean of Graduate Studies and Research at Stanford University

Looking at the hand modulates the brain responses to nociceptive and non-nociceptive somatosensory stimuli but does not necessarily modulate their perception

Previous studies have suggested that looking at the hand can reduce the perception of pain and the magnitude of the ERPs elicited by nociceptive stimuli delivered onto the hand. In contrast, other studies have suggested that looking at the hand can increase tactile sensory discrimination performance, and enhance the magnitude of the ERPs elicited by tactile stimulation. These opposite effects could be related to differences in the crossmodal effects between vision, nociception, and touch. However, these differences could also be related to the use of different experimental designs. Importantly, most studies on the effects of vision on pain have relied on a mirror to create the illusion that the reflected hand is a direct view of the stimulated hand. Here, we compared the effects of direct versus mirror vision of the hand versus an object on the perception and ERPs elicited by non-nociceptive and nociceptive stimuli. We did not observe any significant effect of vision on the perceived intensity. However, vision of the hand did reduce the magnitude of the nociceptive N240 wave, and enhanced the magnitude of the non-nociceptive P200. Our results confirm that vision of the body differentially affects nociceptive and non-nociceptive processing, but question the robustness of visual analgesia.status: publishe

The role of working memory in the attentional control of pain

Attention is acknowledged as an important factor in the modulation of pain. A recent model proposed that an effective control of pain by attention should not only involve the disengagement of selective attention away from nociceptive stimuli, but should also guarantee that attention is maintained on the processing of pain-unrelated information without being recaptured by the nociceptive stimuli. This model predicts that executive functions are involved in the control of selective attention by preserving goal priorities throughout the achievement of cognitive activities. In the present study, we tested the role of working memory in the attentional control of nociceptive stimuli. In the control condition, participants had to discriminate the color of visually presented circles preceded by tactile distracters. In some trials (20%), tactile stimuli were replaced by novel nociceptive distracters in order to manipulate the attentional capture. In the working memory condition, participants had to respond to the visual stimulus presented one trial before, and were thus required to maintain the color of the visual stimulus in working memory during the entire inter-trial time interval. Results showed that, while novel nociceptive stimuli induced greater distraction than regular tactile stimuli in the control condition, the distractive effect was suppressed in the working memory condition. This suggests that actively rehearsing the feature of painunrelated and task-relevant targets successfully prevents attention from being captured by novel nociceptive distracters, independently of general task demands.status: publishe

Capturing with EEG the neural entrainment and coupling underlying sensorimotor synchronization to the beat

Synchronizing movements with rhythmic inputs requires tight coupling of sensory and motor neural processes. Here, using a novel approach based on the recording of steady-state-evoked potentials (SS-EPs), we examine how distant brain areas supporting these processes coordinate their dynamics. The electroencephalogram was recorded while subjects listened to a 2.4-Hz auditory beat and tapped their hand on every second beat. When subjects tapped to the beat, the EEG was characterized by a 2.4-Hz SS-EP compatible with beat-related entrainment and a 1.2-Hz SS-EP compatible with movement-related entrainment, based on the results of source analysis. Most importantly, when compared with passive listening of the beat, we found evidence suggesting an interaction between sensory- and motor-related activities when subjects tapped to the beat, in the form of 1) additional SS-EP appearing at 3.6 Hz, compatible with a nonlinear product of sensorimotor integration; 2) phase coupling of beat- and movement-related activities; and 3) selective enhancement of beat-related activities over the hemisphere contralateral to the tapping, suggesting a top-down effect of movement-related activities on auditory beat processing. Taken together, our results are compatible with the view that rhythmic sensorimotor synchronization is supported by a dynamic coupling of sensory and motor related activities

Dishabituation of Laser-evoked EEG Responses: Dissecting the Effect of Certain and Uncertain Changes in Stimulus Modality

The repetition of nociceptive stimuli of identical modality, intensity, and location at short and constant interstimulus intervals (ISIs) determines a strong habituation of the corresponding EEG responses, without affecting the subjective perception of pain. To understand what determines this response habituation, we (i) examined the effect of introducing a change in the modality of the repeated stimulus, and (ii) dissected the relative contribution of bottom-up, stimulus-driven changes in modality and top-down, cognitive expectations of such a change, on both laser-evoked and auditory-evoked EEG responses. Multichannel EEG was recorded while participants received trains of three stimuli (S1-S2-S3, a triplet) delivered to the hand dorsum at 1-sec ISI. S3 belonged either to the same modality as S1 and S2 or to the other modality. In addition, participants were either explicitly informed or not informed of the modality of S3. We found that introducing a change in stimulus modality produced a significant dishabituation of the laser-evoked N1, N2, and P2 waves; the auditory N1 and P2 waves; and the laser- and auditory-induced event-related synchronization and desynchronization. In contrast, the lack of explicit knowledge of a possible change in the sensory modality of the stimulus (i.e., uncertainty) only increased the ascending portion of the laser-evoked and auditory-evoked P2 wave. Altogether, these results indicate that bottom-up novelty resulting from the change of stimulus modality, and not top-down cognitive expectations, plays a major role in determining the habituation of these brain responses.status: publishe

The effect of heterotopic noxious conditioning stimulation on A-, C- and A-fibre brain responses in humans

Human studies have shown that heterotopic nociceptive conditioning stimulation (HNCS) applied to a given body location reduces the percept and brain responses elicited by noxious test stimuli delivered at a remote body location. It remains unclear to what extent this effect of HNCS relies on the spinal-bulbar-spinal loop mediating the effect of diffuse noxious inhibitory controls (DNICs) described in animals, and/or on top-down cortical mechanisms modulating nociception. Importantly, some studies have examined the effects of HNCS on the brain responses to nociceptive input conveyed by Aδ-fibres. In contrast, no studies have explored the effects of HNCS on the responses to selective nociceptive C-fibre input and non-nociceptive Aβ-fibre input. In this study, we measured the intensity of perception and event-related potentials (ERPs) to stimuli activating Aδ-, C- and Aβ-fibres, before, during and after HNCS, obtained by immersing one foot in painful cold water. We observed that (i) the perceived intensity of nociceptive Aδ- and C-stimuli was reduced during HNCS, and (ii) the ERPs elicited by Aδ- and Aβ- and C-stimuli were also reduced during HNCS. Importantly, because Aβ-ERPs are related to primary afferents that ascend directly through the dorsal columns without being relayed at spinal level, the modulation of these responses may not be explained by an influence of descending projections modulating the transmission of nociceptive input at spinal level. Therefore, our results indicate that, in humans, HNCS should be used with caution as a direct measure of DNIC-related mechanisms.status: publishe

TREKiSM Issue 39

November-December 198

Theta Burst Stimulation Applied over Primary Motor and Somatosensory Cortices Produces Analgesia Unrelated to the Changes in Nociceptive Event-Related Potentials

Continuous theta burst stimulation (cTBS) applied over the primary motor cortex (M1) can alleviate pain although the neural basis of this effect remains largely unknown. Besides, the primary somatosensory cortex (S1) is thought to play a pivotal role in the sensori-discriminative aspects of pain perception but the analgesic effect of cTBS applied over S1 remains controversial. To investigate cTBS-induced analgesia we characterized, in two separate experiments, the effect of cTBS applied either over M1 or S1 on the event-related brain potentials (ERPs) and perception elicited by nociceptive (CO2 laser stimulation) and non-nociceptive (transcutaneous electrical stimulation) somatosensory stimuli. All stimuli were delivered to the ipsilateral and contralateral hand. We found that both cTBS applied over M1 and cTBS applied over S1 significantly reduced the percept elicited by nociceptive stimuli delivered to the contralateral hand as compared to similar stimulation of the ipsilateral hand. In contrast, cTBS did not modulate the perception of non-nociceptive stimuli. Surprisingly, this side-dependent analgesic effect of cTBS was not reflected in the amplitude modulation of nociceptive ERPs. Indeed, both nociceptive (N160, N240 and P360 waves) and late-latency non-nociceptive (N140 and P200 waves) ERPs elicited by stimulation of the contralateral and ipsilateral hands were similarly reduced after cTBS, suggesting an unspecific effect, possibly due to habituation or reduced alertness. In conclusion, cTBS applied over M1 and S1 reduces similarly the perception of nociceptive inputs originating from the contralateral hand, but this analgesic effect is not reflected in the magnitude of nociceptive ERPs.status: publishe