Modulation of Bodily Self-Consciousness by Self and External Touch

The full body illusion (FBI) is a bodily illusion based on the application of multisensory conflicts inducing changes in bodily self-consciousness (BSC), which has been used to study cognitive brain mechanisms underlying body ownership and related aspects of self-consciousness. Typically, such paradigms have employed external passive multisensory stimulation, thus neglecting possible contributions of self-generated action and haptic cue to body ownership. The present paper examined the effects of both external and voluntary self-touch on the BSC with a robotics-based FBI paradigm. We compared the effects of classical passive visuo-tactile stimulation and active self-touch (in which experimental participants have the sense of agency over the tactile stimulation) on the FBI. We evaluated these effects by a questionnaire, a crossmodal congruency task, and measurements of changes in self-location. The results indicated that both the synchronous passive visuo-tactile stimulation and synchronous active self-touch induced illusory ownership over a virtual body, without significant differences in their magnitudes. However, the FBI induced by the active self-touch was associated with larger drift in self-location towards the virtual body. These results show that movement-related signals arising from self-touch impact the BSC not only for hand ownership, but also for torso-centered body ownership and related aspects of BSC.

Neuroscience robotics to investigate multisensory integration and bodily awareness

Olaf Blanke, Dominique Chapuis, Julio Duenas, Roger Gassert, Silvio Ionta, Roberto Martuzzi, Christian Pfeiffer

Humans experience the self as localized within their body. This aspect of bodily self-consciousness can be experimentally manipulated by exposing individuals to conflicting multisensory input, or can be abnormal following focal brain injury. Recent technological developments helped to unravel some of the mechanisms underlying multisensory integration and self-location, but the neural underpinnings are still under investigation, and the manual application of stimuli resulted in large variability difficult to control. This paper presents the development and evaluation of an MR-compatible stroking device capable of presenting moving tactile stimuli to both legs and the back of participants lying on a scanner bed while acquiring functional neuroimaging data. The platform consists of four independent stroking devices with a travel of 16-20 cm and a maximum stroking velocity of 15 cm/s, actuated over non-magnetic ultrasonic motors. Complemented with virtual reality, this setup provides a unique research platform allowing to investigate multisensory integration and its effects on self-location under well-controlled experimental conditions. The MR-compatibility of the system was evaluated in both a 3 and a 7 Tesla scanner and showed negligible interference with brain imaging. In a preliminary study using a prototype device with only one tactile stimulator, fMRI data acquired on 12 healthy participants showed visuo-tactile synchrony-related and body-specific modulations of the brain activity in bilateral temporoparietal cortex.

2012

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

Olaf Blanke, Nathaniel Evans

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

2010

Bodily ownership and self-location: Components of bodily self-consciousness

Christophe Lopez, Andrea Serino

Recent research on bodily self-consciousness has assumed that it consists of three distinct components: the experience of owning a body (body ownership); the experience of being a body with a given location within the environment (self-location); and the experience of taking a first-person, body-centered, perspective on that environment (perspective). Here we review recent neuroimaging studies suggesting that at least two of these components-body ownership and self-location-are implemented in rather distinct neural substrates, located, respectively, in the premotor cortex and in the temporo-parietal junction. We examine these results and consider them in relation to clinical evidence from patients with altered body perception and work on a variety of multisensory, body-related illusions, such as the rubber hand illusion, the full body illusion, the body swap illusion and the enfacement illusion. We conclude by providing a preliminary synthesis of the data on bodily self-consciousness and its neural correlates.

2013

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

Olaf Blanke, Nathaniel Evans

2010