Fully automated modulation of virtual-body ownership supresses fronto-parietal mu rhythm

After continuously applying spatially and temporally congruent visuo-tactile stimulation to external, body-like objects, healthy humans feel the fake part to be the origin of the touch sensations and feel it to be their own. Incongruent stimulation nullifies both illusory changes. This Rubber Hand Illusion (RHI) is the most used paradigm to experimentally investigate healthy humans’ bodily self-consciousness and the extension of body ownership to foreign objects [1]. Standard RHI setups are limited by physical constraints and suffer the disadvantage of imprecise temporo-spatial stimulus control. Further, little is known about the neural and electrophysiological mechanisms associated with the crossmodal conflict and the induced changes in body ownership during the RHI. Here we recorded 64-channel electroencephalography (EEG) to investigate the electrophysiological changes while exposed to a carefully controlled, bilateral RHI induced by haptics and virtual reality (VR) technology. Methods Participants (n=8) sat at a table with a chin rest. Arms were placed (palms up) underneath the table to rest on the legs. A virtual scene depicting the real-world experimental scene was displayed on an immersive Head Mounted Display (HMD). We employed a 2x2 factorial design (Object, Stroking). Participants saw either two arms or two non-body cylinders (Object) projecting from their shoulders onto a virtual table, seeing the virtual arms or cylinder in a position ~20cm above their real arms. Visuo-tactile stimulation was provided by four vibration motors affixed to the palms of the (unseen) left and right hands and by animation of corresponding virtual motors on the virtual hands. Two visuo-tactile modes were defined (Stroking): 1) synchronous: virtual visual motors were shown to vibrate in temporal and spatial synchrony with the tactile vibration motors and 2) asynchronous: virtual visual motors were shown to vibrate with a temporal delay (100±50ms) and a randomly selected spatial direction with respect to the tactile vibration motor pattern. Two additional baseline conditions were recorded (no visual animation of the virtual motors and no tactile stimulation; no visual animation of the virtual motors with tactile stimulation). Subjective experience of the illusion was gauged by a questionnaire. 64-channel EEG was sampled at 2048Hz. Bipolar electrooculograms were recorded for later artifact removal. EEG analysis consisted of breaking 30s of spontaneous EEG data per condition into epochs of 2s. Epochs contaminated with eye blink artifacts or transient changes in electrode-to-scalp conductance were removed. Spectral power changes were computed in three frequency bands: alpha (8-13 Hz), beta (14-30 Hz) and gamma (30-100 Hz). Statistical analysis was performed at the scalp level and included a suprathreshold cluster permutation test to control for Type I errors. The generators of the significant scalp maps were localized with an inverse solution (sLORETA) [2]. Results Repeated ANOVA analysis of the questionnaire indicated a significant interaction between synchrony and question (F=1.65, p=0.03), and a main synchrony effect (F=40.29, p

Self-grounded vision: hand ownership modulates visual location through cortical beta and gamma oscillations

Javier Bello Ruiz, Fosco Bernasconi, Olaf Blanke, Herberto Dhanis Pedro De Barros Camacho, Nathan Quentin Faivre, Roy Salomon, Michele Scandola

Vision is known to be shaped by context, defined by environmental and bodily signals. In the Taylor illusion, the size of an afterimage projected on one's hand changes according to proprioceptive signals conveying hand position. Here, we assessed whether the Taylor illusion does not just depend on the physical hand position, but also on bodily self-consciousness as quantified through illusory hand ownership. Relying on the somatic rubber hand illusion, we manipulated hand ownership, such that participants embodied a rubber hand placed next to their own hand. We found that an afterimage projected on the participant's hand drifted depending on illusory ownership between the participants' two hands, showing an implication of self-representation during the Taylor illusion. Oscillatory power analysis of electroencephalographic signals showed that illusory hand ownership was stronger in participants with stronger alpha suppression over left sensorimotor cortex, whereas the Taylor illusion correlated with higher beta/gamma power over frontotemporal regions. Higher gamma connectivity between left sensorimotor and inferior parietal cortex was also found during illusory hand ownership. These data show that afterimage drifts in the Taylor illusion do not only depend on the physical hand position but also on subjective ownership, which itself is based on the synchrony of somatosensory signals from the two hands. The effect of ownership on afterimage drifts is associated with beta/gamma power and gamma connectivity between frontoparietal regions and the visual cortex. Together, our results suggest that visual percepts are not only influenced by bodily context but are self-grounded, mapped on a self-referential frame.

2017

Shared electrophysiology mechanisms of body ownership and motor imagery

Olaf Blanke, Nathaniel Evans

Although we feel, see, and experience our hands as our own (body or hand ownership), recent research has shown that illusory hand ownership can be induced for fake or virtual hands and may useful for neuroprosthetics and brain-computer interfaces. Despite the vast amount of behavioral data on illusory hand ownership, neuroimaging studies are rare, in particular electrophysiological studies. Thus, while the neural systems underlying hand ownership are relatively well described, the spectral signatures of body ownership as measured by electroencephalography (EEG) remain elusive. Here we induce illusory hand ownership in an automated, computer-controlled manner using virtual reality while recording 64-channel EEG and found that illusory hand ownership is reflected by a body-specific modulation in the mu-band over fronto-parietal cortex. In a second experiment in the same subjects, we then show that mu as well as beta-band activity in highly similar fronto-parietal regions was also modulated during a motor imagery task often used in paradigms employing non-invasive brain-computer interface technology. These data provide insights into the electrophysiological brain mechanisms of illusory hand ownership and their strongly overlapping mechanisms with motor imagery in fronto-parietal cortex. They also highlight the potential of combining high-resolution EEG with virtual reality setups and automatized stimulation protocols for systematic, reproducible stimulus presentation in cognitive neuroscience, and may inform the design of non-invasive brain-computer interfaces.

Academic Press Inc Elsevier Science2013

Multisensory interactions in peripersonal space and their contributions to bodily self-consciousness

Petr Grivaz

What is the relevance of the body and body-transformed sensory information for subjective experience? In the last two decades, paradigms from cognitive neuroscience have demonstrated that the subjective sensations of possessing a body (body ownership, BO), of being located in space (self-location) and being directed at the world (first-person perspective, 1PP), crucially rely on and can be manipulated by exposure to conflicting sensory information in so called bodily illusions. These aspects of subjective experience that are attached to the body, or bodily self-consciousness (BSC), are therefore malleable in healthy participants and accessible to experimental manipulations. BSC is argued to rely on multisensory integration mechanisms within the space directly surrounding the body (i.e. the peripersonal space, PPS). Amply supported by behavioral evidence, data from the brain is sparse. To help elucidate, in terms of neural activity, the relationship between PPS and an aspect of BSC, namely BO, in the first part of my thesis, I will present the results from an fMRI study and a meta-analysis, whereby I globally show that visual and tactile information presented within PPS is processed predominantly within the fronto-parietal and temporo-parietal regions of the brain whereas BO is processed in fronto-parietal and insular regions. Critically, both PPS and BO processing converges only in the left superior parietal cortex (intraparietal sulcus and area 2), thus suggesting both a level of neural integration and dissociation. The subjective 1PP is also argued to rely on multisensory mechanisms and in particular vestibular signals, but the underlying behavioral and neural mechanisms remain largely unexplored. Thus, in the second part of my thesis, I present a behavioral study and a clinical case report. In the prior, we exposed healthy subjects in a supine posture to touch on their backs and synchronous or asynchronous touch on the back of an observed avatar. We further simulated visual gravity using virtual balls falling either in the same or opposite direction with respect to the pull of physical gravity. In line with our expectations, the latter biased the direction of the 1PP to that suggested by the visual gravity (thus subjects reported looking downwards). The visual gravity information also interacted with the synchrony of stroking to affect 1PP and a more frequent downward 1PP was associated with a higher self-elevation rating. Also in line with the idea that BSC and in particular the 1PP relies on multisensory (in particular visuo-vestibular) integration, in the clinical case report we describe a male patient with peripheral vestibulopathy experiencing out-of-body experiences, who fails to integrate visual and vestibular information and is sensitive to visuo-tactile conflicts in bodily illusions. The results from my thesis collectively reinforce the current view that BSC can be manipulated by and thus crucially relies on multisensory mechanisms within PPS as shown both behaviorally for 1PP and in terms of neural correlates for BO. The results also suggest that different combinations of sensory stimuli manipulate most effectively these aspects, with synchronous visuo-tactile stroking affecting BO whereas asynchronous visuo-tactile stroking and vestibular information affecting 1PP. Apprehending better these mechanisms will be an important milestone to understanding how sensory information shapes subjective experience.

EPFL2017

Multisensory interactions in peripersonal space and their contributions to bodily self-consciousness

Petr Grivaz

EPFL2017