Cooling the Thermal Grill Illusion through Self-Touch

Acute peripheral pain is reduced by multisensory interactions at the spinal level. Central pain is reduced by reorganization of cortical body representations. We show here that acute pain can also be reduced by multisensory integration through self-touch, which provides proprioceptive, thermal, and tactile input forming a coherent body representation. We combined self-touch with the thermal grill illusion (TGI). In the traditional TGI, participants press their fingers on two warm objects surrounding one cool object. The warm surround unmasks pain pathways, which paradoxically causes the cool object to feel painfully hot. Here, we warmed the index and ring fingers of each hand while cooling the middle fingers. Immediately after, these three fingers of the right hand were touched against the same three fingers on the left hand. This self-touch caused a dramatic 64% reduction in perceived heat. We show that this paradoxical release from paradoxical heat cannot be explained by low-level touch-temperature interactions alone. To reduce pain, we often clutch a painful hand with the other hand. We show here that self-touch not only gates pain signals reaching the brain but also, via multisensory integration, increases coherence of cognitive body representations to which pain afferents project

Титульні сторінки та зміст

It has recently been shown that contact between one’s own limbs (self-touch) reduces the perceived intensity of pain, over and above the well-known modulation of pain by simultaneous colocalized tactile input Kammers et al. (Curr Biol 20:1819–1822, 2010). Here, we investigate how self-touch modulates somatosensory evoked potentials (SEPs) evoked by afferent somatosensory input. We show that the P100 SEP component, which has previously been implicated in the conscious perception of a tactile stimulus, is enhanced during self-touch, as compared to when one is touching nothing, an inanimate object, or another person. A follow-up experiment showed that there was no effect of self-touch on SEPs when the body parts in contact were not symmetric. Altogether, our findings suggest the interpretation that the secondary somatosensory cortex might underlie the specific analgesic effect of self-touch

The weight of representing the body: addressing the potentially indefinite number of body representations in healthy individuals

There is little consensus about the characteristics and number of body representations in the brain. In the present paper, we examine the main problems that are encountered when trying to dissociate multiple body representations in healthy individuals with the use of bodily illusions. Traditionally, task-dependent bodily illusion effects have been taken as evidence for dissociable underlying body representations. Although this reasoning holds well when the dissociation is made between different types of tasks that are closely linked to different body representations, it becomes problematic when found within the same response task (i.e., within the same type of representation). Hence, this experimental approach to investigating body representations runs the risk of identifying as many different body representations as there are significantly different experimental outputs. Here, we discuss and illustrate a different approach to this pluralism by shifting the focus towards investigating task-dependency of illusion outputs in combination with the type of multisensory input. Finally, we present two examples of behavioural bodily illusion experiments and apply Bayesian model selection to illustrate how this different approach of dissociating and classifying multiple body representations can be applied

How many motoric body representations can we grasp?

At present there is a debate on the number of body representations in the brain. The most commonly used dichotomy is based on the body image, thought to underlie perception and proven to be susceptible to bodily illusions, versus the body schema, hypothesized to guide actions and so far proven to be robust against bodily illusions. In this rubber hand illusion study we investigated the susceptibility of the body schema by manipulating the amount of stimulation on the rubber hand and the participant’s hand, adjusting the postural configuration of the hand, and investigating a grasping rather than a pointing response. Observed results showed for the first time altered grasping responses as a consequence of the grip aperture of the rubber hand. This illusion-sensitive motor response challenges one of the foundations on which the dichotomy is based, and addresses the importance of illusion induction versus type of response when investigating body representations

What is embodiment? a psychometric approach

What is it like to have a body? The present study takes a psychometric approach to this question. We collected structured introspective reports of the rubber hand illusion, to systematically investigate the structure of bodily self-consciousness. Participants observed a rubber hand that was stroked either synchronously or asynchronously with their own hand and then made proprioceptive judgments of the location of their own hand and used Likert scales to rate their agreement or disagreement with 27 statements relating to their subjective experience of the illusion. Principal components analysis of this data revealed four major components of the experience across conditions, which we interpret as: embodiment of rubber hand, loss of own hand, movement, and affect. In the asynchronous condition, an additional fifth component, deafference, was found. Secondary analysis of the embodiment of runner hand component revealed three subcomponents in both conditions: ownership, location, and agency. The ownership and location components were independent significant predictors of proprioceptive biases induced by the illusion. These results suggest that psychometric tools may provide a rich method for studying the structure of conscious experience, and point the way towards an empirically rigorous phenomenology

Is This Hand for Real? Attenuation of the Rubber Hand Illusion by Transcranial Magnetic Stimulation over the Inferior Parietal Lobule

Contains fulltext : 119588-OA.pdf (publisher's version ) (Open Access)In the rubber hand illusion (RHI), participants incorporate a rubber hand into a mental representation of one's body. This deceptive feeling of ownership is accompanied by recalibration of the perceived position of the participant's real hand toward the rubber hand. Neuroimaging data suggest involvement of the posterior parietal lobule during induction of the RHI, when recalibration of the real hand toward the rubber hand takes place. Here, we used off-line low-frequency repetitive transcranial magnetic stimulation (rTMS) in a double-blind, sham-controlled within-subjects design to investigate the role of the inferior posterior parietal lobule (IPL) in establishing the RHI directly. Results showed that rTMS over the IPL attenuated the strength of the RHI for immediate perceptual body judgments only. In contrast, delayed perceptual responses were unaffected. Furthermore, ballistic action responses as well as subjective self-reports of feeling of ownership over the rubber hand remained unaffected by rTMS over the IPL. These findings are in line with previous research showing that the RHI can be broken down into dissociable bodily sensations. The illusion does not merely affect the embodiment of the rubber hand but also influences the experience and localization of one's own hand in an independent manner. Finally, the present findings concur with a multicomponent model of somatosensory body representations, wherein the IPL plays a pivotal role in subserving perceptual body judgments, but not actions or higher-order affective bodily judgments

Being in the dark about your hand : resolution of visuo-proprioceptive conflict by disowning visible limbs

Conflict between sensory modalities can be resolved by one modality overwriting another. For example, movement of a limb that is visible in a stationary visual afterimage results in selective fading of that limb in the afterimage. We investigated the interaction of these two sensory modalities by inducing a mismatch between visual and proprioceptive hand location. Whereas this discrepancy did not affect the initial appearance of the hand in the afterimage, it did prevent subsequent motion with the hand from affecting the hand's appearance. Location mismatch disconnected the visual and proprioceptive experiences of the hand, "protecting" the visual afterimage from interaction with proprioception. Investigation of subjective higher order bodily experiences showed a strong negative correlation between afterimage disruption and the subjective feeling of ownership, suggesting that the brain can resolve multimodal location mismatch by 'disowning' a visible limb, and that the interaction between proprioception and vision is mediated by higher order bodily experiences.6 page(s

Contraction of body representation induced by proprioceptive conflict

Our body is not only an extended object in external space, but also the basis of our sense of self. Proprioceptive signals from muscle spindle organs, specifying body position, play a key role in this unique dual quality of body representation, as they define a ‘here’ or set of locations, where ‘I’ am located [1]. Position information from muscle spindles can be manipulated by vibrating the muscle tendon, generating illusions of position and movement [2]. For example, biceps vibration generates illusions of elbow extension, while triceps vibration generates illusions of flexion. Here we report that proprioceptive conflict induced by simultaneous vibration of antagonistic biceps and triceps muscle tendons alters representation of the body in a way qualitatively different from single vibrations. Rather than relocation or movement, this incoherent conflict of location produces perceived telescoping of the arm towards the elbow. Loss of coherent information about body position in space seems to produce contraction of the body representation itself. Our result suggests that basic sensory signals about body posture also play an essential role in representing the self as an extended object in space

Talking to Teens about Pain:A Modified Delphi Study of Adolescent Pain Science Education

Background: Persistent pain is a prevalent condition that negatively influences physical, emotional, social and family functioning in adolescents. Pain science education is a promising therapy for adults, yet to be thoroughly investigated for persistent pain in adolescents. There is a need to develop suitable curricula for adolescent pain science education. Methods: An interdisciplinary meeting of 12 clinicians and researchers was held during March 2018 in Adelaide, South Australia. An a priori objective of the meeting was to identify and gain consensus on key learning objectives for adolescent pain science education using a modified-Delphi process. Results and Conclusion: Consensus was reached via a modified Delphi process for seven learning objectives to form the foundation of a curriculum: 1) Pain is a protector; 2) The pain system can become overprotective; 3) Pain is a brain output; 4) Pain is not an accurate marker of tissue state; 5) There are many potential contributors to anyone’s pain; 6) We are all bioplastic and; 7) Pain education is treatment. Recommendations are made for promising areas for future research in adolescent pain science education