Cardio-visual full body illusion alters bodily self-consciousness and tactile processing in somatosensory cortex.

Prominent theories highlight the importance of bodily perception for self-consciousness, but it is currently not known whether this is based on interoceptive or exteroceptive signals or on integrated signals from these anatomically distinct systems, nor where in the brain such integration might occur. To investigate this, we measured brain activity during the recently described 'cardio-visual full body illusion' which combines interoceptive and exteroceptive signals, by providing participants with visual exteroceptive information about their heartbeat in the form of a periodically illuminated silhouette outlining a video image of the participant's body and flashing in synchrony with their heartbeat. We found, as also reported previously, that synchronous cardio-visual signals increased self-identification with the virtual body. Here we further investigated whether experimental changes in self-consciousness during this illusion are accompanied by activity changes in somatosensory cortex by recording somatosensory evoked potentials (SEPs). We show that a late somatosensory evoked potential component (P45) reflects the illusory self-identification with a virtual body. These data demonstrate that interoceptive and exteroceptive signals can be combined to modulate activity in parietal somatosensory cortex.

Turning body and self inside out: visualized heartbeats alter bodily self-consciousness and tactile perception.

Prominent theories highlight the importance of bodily perception for self-consciousness, but it is currently not known whether bodily perception is based on interoceptive or exteroceptive signals or on integrated signals from these anatomically distinct systems. In the research reported here, we combined both types of signals by surreptitiously providing participants with visual exteroceptive information about their heartbeat: A real-time video image of a periodically illuminated silhouette outlined participants' (projected, "virtual") bodies and flashed in synchrony with their heartbeats. We investigated whether these "cardio-visual" signals could modulate bodily self-consciousness and tactile perception. We report two main findings. First, synchronous cardio-visual signals increased self-identification with and self-location toward the virtual body, and second, they altered the perception of tactile stimuli applied to participants' backs so that touch was mislocalized toward the virtual body. We argue that the integration of signals from the inside and the outside of the human body is a fundamental neurobiological process underlying self-consciousness.

Experimental changes in bodily self-consciousness are tuned to the frequency sensitivity of proprioceptive fibres.

Several lines of evidence suggest an important implication of proprioceptive signals in bodily self-consciousness. By manipulating proprioceptive signals using muscle vibration, here, we investigated whether such effects depend on the vibration frequency by testing three different vibratory stimuli applied at the lower limbs (20, 40 and 80 Hz). We thus explored whether frequency-specific proprioceptive interference that has been reported in postural or motor tasks will also be found for measures of bodily self-consciousness. Self-identification (questionnaires) and visuotactile integration (asking participants to make tactile discriminations) were quantified during synchronous and asynchronous stroking conditions that are known to manipulate bodily self-consciousness. We found that even though muscle vibrations were applied at the same body location in all cases, 20 Hz vibrations did not alter the magnitude of self-identification and visuotactile integration, whereas 40 and 80 Hz vibrations did. These frequency-specific effects extend earlier vibration effects on motor and postural tasks to bodily self-consciousness. We suggest that the observed changes in bodily self-consciousness are due to altered proprioceptive signals from the lower limbs and that these changes depend on the tuning of Ia fibres to muscle vibration.

Seeing the body modulates audiotactile integration.

Audiotactile integration has been studied using various experimental setups but so far crossmodal congruency effects (CCEs) have not been found for tactile targets paired with auditory distractors. In the present study we investigated whether audiotactile CCEs exist and, if so, whether these CCEs have similar characteristics to those found by previous authors with visual distractors. We measured audiotactile CCEs by attaching four vibrators to the backs of participants and presented auditory stimuli from four loudspeakers placed, in separate blocks, at different distances in front of or behind the participant's body. Participants discriminated the elevation of tactile stimuli while ignoring the auditory distractors. CCEs were found only when participants were provided with noninformative vision of their own body, as seen from behind via a camera and head-mounted display; they were absent when participants did not view their body. Furthermore, in contrast to visuotactile CCEs, audiotactile CCEs did not depend on whether the distractors were presented on the same or different side as the tactile targets. The present study provides the first demonstration of an audiotactile CCE: incongruent auditory distractors impaired performance on a tactile elevation discrimination task relative to performance with congruent distractors. We show that audiotactile CCEs differ from visuotactile CCEs as they do not appear to be as sensitive to the spatial relations between the distractors and the tactile stimuli. We also show that these CCEs are modulated by vision of the body.