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Somatosensory signals and the “I” of conscious experience in healthy subjects and neurological patients

Final Report Summary - SELF-CONSCIOUSNESS (Somatosensory signals and the 'I' of conscious experience in healthy subjects and neurological patients)

The present project addressed key questions on how the representation of the body by the brain contributes to the sense of self. I studied the contribution of somatosensory inputs to bodily self-consciousness in healthy subjects and polyneuropathic patients by using virtual reality and cognitive science in combination with muscle tendon vibrations and brain imaging techniques (EEG). I investigated this in the context of the recently described 'full body illusion' (FBI) that uses visuo-tactile conflicts to alter crucial aspects of bodily self-consciousness such as 'what we feel as our body' (self-identification) and 'where we experience our body to be' (self-location). For the first study, the FBI was associated with vibrations applied at the lower and the upper limbs in order to determine whether bodily self-consciousness was altered by such somatosensory noise in healthy subjects. The data were compatible with our hypothesis of increased visual capture of touch and the integration of proprioceptive signals from the lower limbs with vision and touch for bodily self-consciousness (Palluel et al., 2011).

I carried out a complementary study by investigating whether such effects depended on the vibration frequency. Three different vibratory stimuli applied at the lower limbs (20, 40 and 80 Hz) were used. I explored whether frequency-specific proprioceptive interference that has been reported in postural or motor tasks could also be found for measures of bodily self-consciousness. The results suggested that the observed changes in bodily self-consciousness at 40 and 80 Hz (but not at 20 Hz) were due to altered proprioceptive signals from the lower limbs and that these changes depended on the tuning of Ia fibres to muscle vibration (Palluel et al., 2012).

I also investigated whether experimental changes in self-identification during the FBI were accompanied by activity changes in somatosensory cortex by recording somatosensory evoked potentials (SEPs). Tibial nerve SEPs were recorded during the FBI and analysed using evoked potential (EP) mapping. The data showed that changes in bodily self-consciousness modulated activity in primary and higher-tier somatosensory cortex at two distinct processing steps. Activation at 30-50 ms (corresponding to the P40 component) in primary somatosensory cortex was stronger in the illusion condition. A later activation at approximately 110-200 ms, likely originating in higher-tier somatosensory regions in parietal cortex, was stronger and lasted longer in the control condition. We presented arguments that early modulations of primary somatosensory cortex may be a consequence of a functional deafferentation resulting from loss of self-identification with the physical body while the SEP effects at longer latencies in higher-tier regions may be related to the detection of greater visuo-tactile incongruency in the asynchronous control condition. (Aspell et al., 2012).

This proposal was highly original in its combination of high-quality quantitative psychophysical and neuroimaging studies of fundamental body perception with deep neuroscientific and philosophical questions about the neural basis of the self. We are now extending this research line to paraplegic patients to understand the brain's body representation and address the question whether and how the sense of the bodily self is altered in this population. We are also investigating whether pain in paraplegic patients depends differently on body representation and the bodily self than in control subjects.

Aspell JE, Palluel E and Blanke O. (2012). Early and late activity in somatosensory cortex reflects changes in bodily self-consciousness: An evoked potential study. Neuroscience.

Palluel E, Aspell JE and Blanke O. (2011). Leg muscle vibration modulates bodily self-consciousness: integration of proprioceptive, visual, and tactile signals. J Neurophysiol 105, 2239-2247.

Palluel E, Aspell JE, Lavanchy T and Blanke O. (2012). Experimental changes in bodily self-consciousness are tuned to the frequency sensitivity of proprioceptive fibres. Neuroreport 23, 354-359.