Evidence that subclinical somatoform dissociation is not characterised by heightened awareness of proprioceptive signals

Introduction: It has been suggested that abnormal perceptual processing and somatosensory amplification may be contributory factors to somatoform symptom reporting. A key source of somatosensory information is proprioception, yet the perception and integration of this sense has not been sufficiently investigated in those prone to somatoform disorders. Methods: Subclinical groups of high- and low-scorers on the Somatoform Dissociation Questionnaire made judgements about the location of their unseen hand following congruent or incongruent visuo-proprioceptive feedback, which was manipulated using a MIRAGE-mediated reality system. Results: No differences were found between groups, with both groups displaying normal proprioceptive accuracy under congruent conditions and equivalent visuo-proprioceptive integration under incongruent conditions. Conclusions: The results suggest that amplification of, or abnormal weighting for, proprioceptive signals is not a contributing factor to somatoform symptom reporting

Spatial compression impairs prism adaptation in healthy individuals

Neglect patients typically present with gross inattention to one side of space following damage to the contralateral hemisphere. While prism-adaptation (PA) is effective in ameliorating some neglect behaviors, the mechanisms involved and their relationship to neglect remain unclear. Recent studies have shown that conscious strategic control (SC) processes in PA may be impaired in neglect patients, who are also reported to show extraordinarily long aftereffects compared to healthy participants. Determining the underlying cause of these effects may be the key to understanding therapeutic benefits. Alternative accounts suggest that reduced SC might result from a failure to detect prism-induced reaching errors properly either because (a) the size of the error is underestimated in compressed visual space or (b) pathologically increased error-detection thresholds reduce the requirement for error correction. The purpose of this study was to model these two alternatives in healthy participants and to examine whether SC and subsequent aftereffects were abnormal compared to standard PA. Each participant completed three PA procedures within a MIRAGE mediated reality environment with direction errors recorded before, during and after adaptation. During PA, visual feedback of the reach could be compressed, perturbed by noise, or represented veridically. Compressed visual space significantly reduced SC and aftereffects compared to control and noise conditions. These results support recent observations in neglect patients, suggesting that a distortion of spatial representation may successfully model neglect and explain neglect performance while adapting to prisms

Spatial compression impairs prism adaptation in healthy individuals

Neglect patients typically present with gross inattention to one side of space following damage to the contralateral hemisphere. While prism-adaptation (PA) is effective in ameliorating some neglect behaviors, the mechanisms involved and their relationship to neglect remain unclear. Recent studies have shown that conscious strategic control (SC) processes in PA may be impaired in neglect patients, who are also reported to show extraordinarily long aftereffects compared to healthy participants. Determining the underlying cause of these effects may be the key to understanding therapeutic benefits. Alternative accounts suggest that reduced SC might result from a failure to detect prism-induced reaching errors properly either because (a) the size of the error is underestimated in compressed visual space or (b) pathologically increased error-detection thresholds reduce the requirement for error correction. The purpose of this study was to model these two alternatives in healthy participants and to examine whether SC and subsequent aftereffects were abnormal compared to standard PA. Each participant completed three PA procedures within a MIRAGE mediated reality environment with direction errors recorded before, during and after adaptation. During PA, visual feedback of the reach could be compressed, perturbed by noise, or represented veridically. Compressed visual space significantly reduced SC and aftereffects compared to control and noise conditions. These results support recent observations in neglect patients, suggesting that a distortion of spatial representation may successfully model neglect and explain neglect performance while adapting to prisms

The Anne Boleyn Illusion is a six-fingered salute to sensory remapping

The Anne Boleyn Illusion exploits the somatotopic representation of touch to create the illusion of an extra digit and demonstrates the instantaneous remapping of relative touch location into body-based coordinates through visuo-tactile integration. Performed successfully on thousands, it is also a simple demonstration of the flexibility of body representations for use at public events, in schools or in the home and can be implemented anywhere by anyone with a mirror and some degree of bimanual coordination

Evidence that subclinical somatoform dissociation is not characterised by heightened awareness of proprioceptive signals

Introduction: It has been suggested that abnormal perceptual processing and somatosensory amplification may be contributory factors to somatoform symptom reporting. A key source of somatosensory information is proprioception, yet the perception and integration of this sense has not been sufficiently investigated in those prone to somatoform disorders.Methods: Subclinical groups of high- and low-scorers on the Somatoform Dissociation Questionnaire made judgements about the location of their unseen hand following congruent or incongruent visuo-proprioceptive feedback, which was manipulated using a MIRAGE-mediated reality system.Results: No differences were found between groups, with both groups displaying normal proprioceptive accuracy under congruent conditions and equivalent visuo-proprioceptive integration under incongruent conditions.Conclusions: The results suggest that amplification of, or abnormal weighting for, proprioceptive signals is not a contributing factor to somatoform symptom reporting

The effect of visual, spatial and temporal manipulations on embodiment and action

The feeling of owning and controlling the body relies on the integration and interpretation of sensory input from multiple sources with respect to existing representations of the bodily self. Illusion paradigms involving multisensory manipulations have demonstrated that while the senses of ownership and agency are strongly related, these two components of bodily experience may be dissociable and differentially affected by alterations to sensory input. Importantly, however, much of the current literature has focused on the application of sensory manipulations to external objects or virtual representations of the self that are visually incongruent with the viewer’s own body and which are not part of the existing body representation. The current experiment used MIRAGE-mediated reality to investigate how manipulating the visual, spatial and temporal properties of the participant’s own hand (as opposed to a fake/virtual limb) affected embodiment and action. Participants viewed two representations of their right hand inside a MIRAGE multisensory illusions box with opposing visual (normal or grossly distorted), temporal (synchronous or asynchronous) and spatial (precise real location or false location) manipulations applied to each hand. Subjective experiences of ownership and agency towards each hand were measured alongside an objective measure of perceived hand location using a pointing task. The subjective sense of agency was always anchored to the synchronous hand, regardless of physical appearance and location. Subjective ownership also moved with the synchronous hand, except when both the location and appearance of the synchronous limb were incongruent with that of the real limb. Objective pointing measures displayed a similar pattern, however movement synchrony was not sufficient to drive a complete shift in perceived hand location, indicating a greater reliance on the spatial location of the real hand. The results suggest that while the congruence of self-generated movement is a sufficient driver for the sense of agency, the sense of ownership is additionally sensitive to cues about the visual appearance and spatial location of one’s own body

An exploratory investigation into the longevity of pain reduction following multisensory illusions designed to alter body perception

BACKGROUND: Previous research suggests that multisensory body illusions that alter the conscious bodily experience can modulate pain in osteoarthritis, which may be a result of modifying cortical misrepresentations of the painful body part. However, the longevity and underlying mechanisms of such illusion-induced analgesia is unknown. OBJECTIVES: This study aimed to investigate the therapeutic potential of body illusions, specifically examining the longevity of pain relief and effects on subjective joint flexibility. We also aimed to test if illusory-induced analgesia was due to limb disownership, which is also thought to be affected by body illusions. METHOD: Multisensory stretch and shrink illusions were used to manipulate mental representations in hand osteoarthritis. Experiment 1 examined longevity of analgesia by comparing pre-illusion pain ratings with post-illusion ratings taken immediately and over a period of four minutes both with and without vision of the manipulated limb. Experiment 2 compared changes in subjective flexibility between the illusion types. Experiment 3 tested whether an illusion that induced a temporary experience of hand loss would indicate limb disownership as a mechanism for modulating pain during body illusions. RESULTS: Illusion-induced analgesia was found to outlast the direct application of both shrink and stretch illusions. Illusory stretching provided more clinically significant pain reduction along with increased subjective flexibility. Disownership of the limb had no effect on pain ratings. CONCLUSIONS: Illusory stretching of the joints in osteoarthritis may have significant clinical potential in development of future pain treatments. The results are also compatible with theories of cortical involvement of pain in osteoarthritis

Transcranial direct current stimulation (tDCS): A beginner’s guide for design and implementation

Transcranial direct current stimulation (tDCS) is a popular brain stimulation method that is used to modulate cortical excitability, producing facilitatory or inhibitory effects upon a variety of behaviors. There is, however, a current lack of consensus between studies, with many results suggesting that polarity-specific effects are difficult to obtain. This article explores some of these differences and highlights the experimental parameters that may underlie their occurrence. We provide a general, practical snapshot of tDCS methodology, including what it is used for, how to use it, and considerations for designing an effective and safe experiment. Our aim is to equip researchers who are new to tDCS with the essential knowledge so that they can make informed and well-rounded decisions when designing and running successful experiments. By summarizing the varied approaches, stimulation parameters, and outcomes, this article should help inform future tDCS research in a variety of fields

Increased somatic sensations are associated with reduced limb ownership

Objective: Medically unexplained symptoms (MUS) are increasingly being thought of as resulting from dysfunctional modulation of interoceptive sensory signals by top-down cognitive processes. The current study investigated whether individuals with a tendency toward MUS would be more susceptible to visual illusions that suggest tactile sensation on the skin in the absence of any actual somatosensory input. Method: Participants viewed real-time mediated reality video images of their own hand, either un-manipulated or digitally altered to display moving pixelated ‘static’ effect; the crawling skin illusion. The strength of various physical sensations during each condition were rated on a numeric scale and compared to standard measures of somatoform dissociation (Somatoform Dissociation Questionnaire 20). Results: Participants reporting a higher degree of somatoform dissociation were found to be more susceptible to somatic sensations across all conditions. Interestingly, participants who reported more visually-induced somatosensory sensations also felt less ownership over their digitally-presented hands. Conclusion: These findings support the proposed link between MUS and disturbances in body representation, and suggest that an over-reliance on top-down knowledge may interfere with current sensory inputs - contributing to symptom formation and maintenance in susceptible individuals

The effect of visual, spatial and temporal manipulations on embodiment and action

The feeling of owning and controlling the body relies on the integration and interpretation of sensory input from multiple sources with respect to existing representations of the bodily self. Illusion paradigms involving multisensory manipulations have demonstrated that while the senses of ownership and agency are strongly related, these two components of bodily experience may be dissociable and differentially affected by alterations to sensory input. Importantly, however, much of the current literature has focused on the application of sensory manipulations to external objects or virtual representations of the self that are visually incongruent with the viewer’s own body and which are not part of the existing body representation. The current experiment used MIRAGE-mediated reality to investigate how manipulating the visual, spatial and temporal properties of the participant’s own hand (as opposed to a fake/virtual limb) affected embodiment and action. Participants viewed two representations of their right hand inside a MIRAGE multisensory illusions box with opposing visual (normal or grossly distorted), temporal (synchronous or asynchronous) and spatial (precise real location or false location) manipulations applied to each hand. Subjective experiences of ownership and agency towards each hand were measured alongside an objective measure of perceived hand location using a pointing task. The subjective sense of agency was always anchored to the synchronous hand, regardless of physical appearance and location. Subjective ownership also moved with the synchronous hand, except when both the location and appearance of the synchronous limb were incongruent with that of the real limb. Objective pointing measures displayed a similar pattern, however movement synchrony was not sufficient to drive a complete shift in perceived hand location, indicating a greater reliance on the spatial location of the real hand. The results suggest that while the congruence of self-generated movement is a sufficient driver for the sense of agency, the sense of ownership is additionally sensitive to cues about the visual appearance and spatial location of one’s own body