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Experiencing the body as a coherent, stable, entity involves the dynamic integration of information from several internal (i.e. interoceptive) and external (i.e. exteroceptive) sensory sources, to produce a feeling that the body is mine (sense of body ownership), that I am in control (sense of agency) and I am aware of its movements (motor awareness). However, the exact contribution of these different sensory sources to self-consciousness, as well as the context in which we experience them, is still a matter of debate. This thesis aimed to investigate the neurocognitive mechanisms of body ownership, agency and motor awareness, including interoceptive (via affective touch), proprioceptive, exteroceptive (visuo-spatial) and vestibular contributions to body representation, in both healthy subjects and brain damaged patients. To examine the role of the vestibular and interoceptive systems in body ownership, a series of studies in healthy subjects was devised, using multisensory illusions (i.e. the rubber hand illusion; RHI), that involve the integration of interoceptive and exteroceptive sensory sources, and using electrical stimulation of the vestibular system (i.e. Galvanic Vestibular Stimulation; GVS). To investigate ownership, agency and motor awareness in neuropsychological patients with disorders of ownership and/or unawareness of motor deficits, behavioural manipulation of body ownership (via a rubber hand) and visual perspective (via a mirror) were tested. Finally, to explore underlying mechanisms of awareness of one’s own performance (i.e. meta-cognition), two studies were carried out in healthy subjects using behavioural manipulations of spatial reference frames (either centred on the subject, i.e. egocentric, or world-centred, i.e. allocentric). The results of these studies indicate that the vestibular system balances vision and proprioception according to contextual relevance: when there is no tactile stimulation, visual cues are stronger than proprioceptive ones (i.e. proprioceptive drifts are greater); when touch is delivered synchronously, this effect is enhanced (even more when touch is affective rather than neutral). However, when touch is only felt but not seen, the vestibular system downregulates vision in favour of proprioception (i.e. proprioceptive drifts are smaller), whilst the opposite happens when touch is only vicariously perceived via vision. Nevertheless, when the rubber hand is positioned in a non-biomechanically possible fashion, there appears to be no difference in proprioceptive drifts in comparison with anatomically plausible positions, suggesting that such rebalancing may be more related to basic multisensory integration processes underlying body representation. In patients with disorders of the self, visual cues seem to dominate over proprioceptive ones, leading to strong feelings of ownership of a rubber hand following mere exposure to it; however, the same is not true for agency, which seems to be more susceptible to changes in the environment (i.e. presence or absence of a visual feedback following attempted movement). Moreover, manipulating visual perspective using a mirror (from 1st to 3rd) seem to lead to a temporary remission of dis-ownership but not motor unawareness, suggesting that awareness may not be influenced by online changes in visual perspectives. Finally, when judging their own performance in a visuo-proprioceptive task from an egocentric rather than an allocentric perspective, healthy subjects appear less objective prospectively rather than during the task (i.e. their belief updating is biased when judging their ability to complete a task egocentrically). In sum, the work described above adds to the evidence that the sense of self derives from a complex integration of several sensory modalities, flexibly adjusting to the environment. Following brain damage, such flexibility may be impaired, even though it can be influenced by spatial perspective. Similarly, the point of reference from which we perceive stimuli affects the way we judge our own perceptual choices. Hence, the way we represent our bodily self is a dynamic process, constantly updated by exteroceptive and interoceptive incoming stimuli, regulated by the vestibular system. These findings could provide new avenues in rehabilitating disorders of the self (such as unawareness and dis-ownership).

In the last decade, neuroscience and psychology alike have paid increasing attention to the study of affective touch, which refers to the emotional and motivational facets of tactile sensation. Some aspects of affective touch have been linked to a neurophysiologically specialised system, namely the C tactile (CT) system. While the role of this system for affiliation, social bonding and communication of emotions have been investigated, less is known about the potential role of affective touch in the awareness of the body as our own, i.e. as belonging to our psychological 'self'. This thesis attempted to contribute to the knowledge on affective touch and its relation to body awareness, by exploring the potential role of this modality to the way we perceive and make sense of our body as our own. Specifically, this work aimed to advance the current state of knowledge by investigating: 1) the effect of affective touch on the sense of body ownership, which is a fundamental aspect of body awareness; 2) the relation between interoceptive modalities, originating both internally (i.e. cardiac awareness) and peripherally (i.e. affective touch), and exteroception in body awareness; 3) the effect of intranasal oxytocin on the perception of affective touch and bodily awareness; 4) the perception and social modulation of affective touch in psychiatric patients who show difficulties in body awareness, namely patients with Anorexia Nervosa, and 5) the modulating role of self-other distinction and of self-other relation in the perception of affective touch and body awareness. In a first experiment (N = 52) the rubber hand illusion paradigm was used to investigate the role played by CT-optimal, affective touch in the sense of body ownership. The results showed that slow, pleasant touch enhanced the experience of embodiment in comparison to faster, neutral touch, suggesting that affective touch might uniquely contribute to the sense of body ownership. The following study (N = 75), used a similar methodology to test whether interoceptive sensitivity as measured by a heartbeat counting task would modulate the extent to which affective touch influences the multisensory process taking place during the rubber hand illusion. The results could not confirm a systematic relation between interoceptive sensitivity and the perception of affective touch, nor its influence on body ownership. The next study (N = 41) included a double-blind, placebo-controlled, randomised, cross-over design testing the effect of intranasal oxytocin on the perception of affective touch and body ownership, as measured by means of the rubber hand illusion. There was no evidence supporting the hypothesis that intranasal oxytocin could influence the CT system as tested in this study. The next study (N = 55) applied some of the above methodologies to investigate the perception of CT-optimal touch in patients with anorexia nervosa and its emotional modulation by top-down factors. The results confirmed the hypothesis that people with anorexia nervosa show a reduced perception of affective touch compared to healthy controls, but its perception was not influenced by top-down affective modulation, in the sense that both patients and healthy controls perceived touch as more pleasant when presented concurrently with positive facial expressions compared to neutral and negative faces. Finally, the last two studies (N = 76 and 35 healthy volunteers, respectively) focused on the relationship between affective touch and body awareness in the context of social cognition. These studies used both online and offline social modulation paradigms to investigate the role of self-other distinction and of self-other relation in the perception of affective touch. The results showed that positive top-down social information can enhance the perceived pleasure of tactile stimulation. Taken together, these studies point to the central role of affective touch in body awareness and social cognition. Finally, they also pave the way for future studies examining the role of disruptions of the CT system in the development of neuropsychiatric impairments of body awareness and social cognition.