Pain and Body Awareness: Evidence from Brain-Damaged Patients with Delusional Body Ownership

A crucial aspect for the cognitive neuroscience of pain is the interplay between pain perception and body awareness. Here we report a novel neuropsychological condition in which right brain-damaged patients displayed a selective monothematic delusion of body ownership. Specifically, when both their own and the co-experimenter's left arms were present, these patients claimed that the latter belonged to them. We reasoned that this was an ideal condition to examine whether pain perception can be "referred" to an alien arm subjectively experienced as one's own. Seventeen patients (11 with, 6 without the delusion), and 10 healthy controls were administered a nociceptive stimulation protocol to assess pain perception. In the OWN condition, participants placed their arms on a table in front of them. In the ALIEN condition, the co-experimenter's left (or right) arm was placed alongside the participants' left (or right) arm, respectively. In the OWN condition, left (or right) participants' hand dorsum were stimulated. In the ALIEN condition, left (or right) co-experimenter's hand dorsum was stimulated. Participants had to rate the perceived pain on a 0-5 Likert scale (0\u2009=\u2009no pain, 5\u2009=\u2009maximal imaginable pain). Results showed that healthy controls and patients without delusion gave scores higher than zero only when their own hands were stimulated. On the contrary, patients with delusion gave scores higher than zero both when their own hands (left or right) were stimulated and when the co-experimenter's left hand was stimulated. Our results show that in pathological conditions, a body part of another person can become so deeply embedded in one's own somatosensory representation to effect the subjective feeling of pain. More in general, our findings are in line with a growing number of evidence emphasizing the role of the special and unique perceptual status of body ownership in giving rise to the phenomenological experience of pain

Bodily ownership modulation in defensive responses: Physiological evidence in brain-damaged patients with pathological embodiment of other's body parts

Do conscious beliefs about the body affect defensive mechanisms within the body? To answer this question we took advantage from a monothematic delusion of bodily ownership, in which brain-damaged patients misidentify alien limbs as their own. We investigated whether the delusional belief that an alien hand is their own hand modulates a subcortical defensive response, such as the hand-blink reflex. The blink, dramatically increases when the threated hand is inside the defensive peripersonal-space of the face. In our between-subjects design, including patients and controls, the threat was brought near the face either by the own hand or by another person’s hand. Our results show an ownership-dependent modulation of the defensive response. In controls, as well as in the patients’ intact-side, the response enhancement is significantly greater when the threat was brought near the face by the own than by the alien hand. Crucially, in the patients’ affected-side (where the pathological embodiment occurs), the alien (embodied) hand elicited a response enhancement comparable to that found when the threat is brought near the face by the real hand. These findings suggest the existence of a mutual interaction between our conscious beliefs about the body and the physiological mechanisms within the body

Multisensory-driven facilitation within the peripersonal space is modulated by the expectations about stimulus location on the body

Compelling evidence from human and non-human studies suggests that responses to multisensory events are fastened when stimuli occur within the space surrounding the bodily self (i.e., peripersonal space; PPS). However, some human studies did not find such effect. We propose that these dissonant voices might actually uncover a specific mechanism, modulating PPS boundaries according to sensory regularities. We exploited a visuo-tactile paradigm, wherein participants provided speeded responses to tactile stimuli and rated their perceived intensity while ignoring simultaneous visual stimuli, appearing near the stimulated hand (VTNear) or far from it (VTFar; near the non-stimulated hand). Tactile stimuli could be delivered only to one hand (unilateral task) or to both hands randomly (bilateral task). Results revealed that a space-dependent multisensory enhancement (i.e., faster responses and higher perceived intensity in VTNear than VTFar) was present when highly predictable tactile stimulation induced PPS to be circumscribed around the stimulated hand (unilateral task). Conversely, when stimulus location was unpredictable (bilateral task), participants showed a comparable multisensory enhancement in both bimodal conditions, suggesting a PPS widening to include both hands. We propose that the detection of environmental regularities actively shapes PPS boundaries, thus optimizing the detection and reaction to incoming sensory stimuli