The feeling of " ownership " over an external dummy/virtual body (or body part) has been proven t... more The feeling of " ownership " over an external dummy/virtual body (or body part) has been proven to have both physiological and behavioural consequences. For instance, the vision of an " embodied " dummy or virtual body can modulate pain perception. However, the impact of partial or total invisibility of the body on physiology and behaviour has been hardly explored since it presents obvious difficulties in the real world. In this study we explored how body transparency affects both body ownership and pain threshold. By means of virtual reality, we presented healthy participants with a virtual co-located body with four different levels of transparency, while participants were tested for pain threshold by increasing ramps of heat stimulation. We found that the strength of the body ownership illusion decreases when the body gets more transparent. Nevertheless, in the conditions where the body was semi-transparent, higher levels of ownership over a see-through body resulted in an increased pain sensitivity. Virtual body ownership can be used for the development of pain management interventions. However, we demonstrate that providing invisibility of the body does not increase pain threshold. Therefore, body transparency is not a good strategy to decrease pain in clinical contexts, yet this remains to be tested. Visual feedback has been shown to effectively modulate pain sensations in experimental studies with both healthy participants and chronic pain patients 1–4. In particular, there is increasing evidence from pain studies showing how vision of the body may lead to effective pain relief 5–10. For instance, in a seminal study by Longo and co-workers, it was shown that the vision of one's hand produces analgesic effects compared to when the gaze is oriented toward an object or another's hand 5. In the same study the authors demonstrated that the attenuated behavioural response was paralleled by a significant decrease in the brain response elicited by the nociceptive stimuli. Further experimental research has confirmed that there is an effective interaction between the vision of the body and the sensation of pain. For example Mancini and co-workers demonstrated that the visual size of someone's own hand manipulated through mirrors leads to modulation of the pain threshold. In particular these authors reported that the vision of a smaller hand seen through a concave mirror leads to a higher pain threshold, while the vision of
Chronic pain is often associated with sleep disruption, fatigue, cognitive deficits and mood alte... more Chronic pain is often associated with sleep disruption, fatigue, cognitive deficits and mood alterations. In particular a bidirectional relationship exists between pain and mood disorders, for example chronic pain and depression. When these morbidities co-occur, the patient’s quality of life can significantly decrease. Different pharmacological solutions have been proposed to target both symptom atologies but misuse, addiction and side effects may limit their adoption. Non-pharmacological interventions like psychotherapy and physical activity have been shown to yield promising results in the management of both chronic pain and mood disorders. In the last twenty years multisensory feedback approaches based on body representation have also been shown to be a valid method to treat different forms of chronic pain. However, comorbid mood disorders have not been taken in consideration by this latter approach. The advances in the treatment of chronic pain with comorbid depression may benefit from future studies using multisensory feedback approaches based on body representation.
Previous studies have demonstrated that the vision of one's own body, or of external embodied lim... more Previous studies have demonstrated that the vision of one's own body, or of external embodied limbs, can lead to pain relieving outcomes. Analgesic effects have also been related to the vision of illusory limb movements. Nonetheless, whether these two processes can be put together to obtain a summatory analgesic effect is not yet clear. The aim of this work was to investigate if it is possible to combine the analgesic effects of looking at one's own body with those deriving from the illusion that one's own limb is moving. Thirty-eight healthy participants underwent four visual conditions in immersive virtual reality while their heat pain thresholds were measured. In different conditions the subject watched from a first-person perspective: i) a still virtual arm, ii) a moving virtual arm, iii) a still non-corporeal object, and iv) a moving non-corporeal object. All participants were asked to keep their arms completely still during the visual exposures. After each condition, participants answered questions about their illusory experience. Our results show that the vision of the 'own' body significantly increased participants' pain threshold as compared to the vision of the non-corporeal object. However, no statistically significant analgesic effect of vision of the virtual arm movement was found. The implications and limitations of this study are discussed.
It has been demonstrated that visual inputs can modulate pain. However, the influence of skin col... more It has been demonstrated that visual inputs can modulate pain. However, the influence of skin color on pain perception is unknown. Red skin is associated to inflamed, hot and more sensitive skin, while blue is associated to cyanotic, cold skin. We aimed to test whether the color of the skin would alter the heat pain threshold. To this end, we used an immersive virtual environment where we induced embodiment of a virtual arm that was co-located with the real one and seen from a first-person perspective. Virtual reality allowed us to dynamically modify the color of the skin of the virtual arm. In order to test pain threshold, increasing ramps of heat stimulation applied on the participants' arm were delivered con-comitantly with the gradual intensification of different colors on the embodied avatar's arm. We found that a reddened arm significantly decreased the pain threshold compared with normal and bluish skin.This effect was specific when red was seen on the arm, while seeing red in a spot outside the arm did not decrease pain threshold. These results demonstrate an influence of skin color on pain perception. This top-down modulation of pain through visual input suggests a potential use of embodied virtual bodies for pain therapy.
Despite the increasing interest in twin studies and the stunning amount of research on face recog... more Despite the increasing interest in twin studies and the stunning amount of research on face recognition, the ability of adult identical twins to discriminate their own faces from those of their co-twins has been scarcely investigated. One's own face is the most distinctive feature of the bodily self, and people typically show a clear advantage in recognizing their own face even more than other very familiar identities. Given the very high level of resemblance of their faces, monozygotic twins represent a unique model for exploring self-face processing. Herein we examined the ability of monozygotic twins to distinguish their own face from the face of their co-twin and of a highly familiar individual. Results show that twins equally recognize their own face and their twin's face. This lack of self-face advantage was negatively predicted by how much they felt physically similar to their co-twin and by their anxious or avoidant attachment style. We speculate that in monozygotic twins, the visual representation of the self-face overlaps with that of the co-twin. Thus, to distinguish the self from the co-twin, monozygotic twins have to rely much more than control participants on the multi-sensory integration processes upon which the sense of bodily self is based. Moreover, in keeping with the notion that attachment style influences perception of self and significant others, we propose that the observed self/co-twin confusion may depend upon insecure attachment.
Understanding the mental states of others entails a number of cognitive processes known as Theory... more Understanding the mental states of others entails a number of cognitive processes known as Theory of Mind (ToM). A relationship between ToM deficits and executive disorders has been hypothesized in individuals with Parkinson's disease (PD). The present study was aimed at investigating the effect of dysexecutive deficits on ToM abilities in PD patients without dementia. Participants included 30 PD patients and 30 healthy subjects (HC). PD patients were divided into two groups according to their executive test performance: patients with poor (dysexecutive group; n=15) and normal (executively unimpaired group; n=15) performance. All participants were administered faux pas recognition written stories. The dysexecutive PD patients performed less accurately than both HC and executively unimpaired PD individuals on all faux pas story questions (p< 0.05); the executively unimpaired PD group performed as accurately as the HC group on the ToM tasks. Results of the study clearly demonstrate that PD is not tout court associated with ToM impairments and that these may occur in PD patients as a function of the degree of their executive impairment. Our findings also indirectly confirm previous data on the role of the prefrontal regions in mediating ToM capacities.
The feeling of " ownership " over an external dummy/virtual body (or body part) has been proven t... more The feeling of " ownership " over an external dummy/virtual body (or body part) has been proven to have both physiological and behavioural consequences. For instance, the vision of an " embodied " dummy or virtual body can modulate pain perception. However, the impact of partial or total invisibility of the body on physiology and behaviour has been hardly explored since it presents obvious difficulties in the real world. In this study we explored how body transparency affects both body ownership and pain threshold. By means of virtual reality, we presented healthy participants with a virtual co-located body with four different levels of transparency, while participants were tested for pain threshold by increasing ramps of heat stimulation. We found that the strength of the body ownership illusion decreases when the body gets more transparent. Nevertheless, in the conditions where the body was semi-transparent, higher levels of ownership over a see-through body resulted in an increased pain sensitivity. Virtual body ownership can be used for the development of pain management interventions. However, we demonstrate that providing invisibility of the body does not increase pain threshold. Therefore, body transparency is not a good strategy to decrease pain in clinical contexts, yet this remains to be tested. Visual feedback has been shown to effectively modulate pain sensations in experimental studies with both healthy participants and chronic pain patients 1–4. In particular, there is increasing evidence from pain studies showing how vision of the body may lead to effective pain relief 5–10. For instance, in a seminal study by Longo and co-workers, it was shown that the vision of one's hand produces analgesic effects compared to when the gaze is oriented toward an object or another's hand 5. In the same study the authors demonstrated that the attenuated behavioural response was paralleled by a significant decrease in the brain response elicited by the nociceptive stimuli. Further experimental research has confirmed that there is an effective interaction between the vision of the body and the sensation of pain. For example Mancini and co-workers demonstrated that the visual size of someone's own hand manipulated through mirrors leads to modulation of the pain threshold. In particular these authors reported that the vision of a smaller hand seen through a concave mirror leads to a higher pain threshold, while the vision of
Chronic pain is often associated with sleep disruption, fatigue, cognitive deficits and mood alte... more Chronic pain is often associated with sleep disruption, fatigue, cognitive deficits and mood alterations. In particular a bidirectional relationship exists between pain and mood disorders, for example chronic pain and depression. When these morbidities co-occur, the patient’s quality of life can significantly decrease. Different pharmacological solutions have been proposed to target both symptom atologies but misuse, addiction and side effects may limit their adoption. Non-pharmacological interventions like psychotherapy and physical activity have been shown to yield promising results in the management of both chronic pain and mood disorders. In the last twenty years multisensory feedback approaches based on body representation have also been shown to be a valid method to treat different forms of chronic pain. However, comorbid mood disorders have not been taken in consideration by this latter approach. The advances in the treatment of chronic pain with comorbid depression may benefit from future studies using multisensory feedback approaches based on body representation.
Previous studies have demonstrated that the vision of one's own body, or of external embodied lim... more Previous studies have demonstrated that the vision of one's own body, or of external embodied limbs, can lead to pain relieving outcomes. Analgesic effects have also been related to the vision of illusory limb movements. Nonetheless, whether these two processes can be put together to obtain a summatory analgesic effect is not yet clear. The aim of this work was to investigate if it is possible to combine the analgesic effects of looking at one's own body with those deriving from the illusion that one's own limb is moving. Thirty-eight healthy participants underwent four visual conditions in immersive virtual reality while their heat pain thresholds were measured. In different conditions the subject watched from a first-person perspective: i) a still virtual arm, ii) a moving virtual arm, iii) a still non-corporeal object, and iv) a moving non-corporeal object. All participants were asked to keep their arms completely still during the visual exposures. After each condition, participants answered questions about their illusory experience. Our results show that the vision of the 'own' body significantly increased participants' pain threshold as compared to the vision of the non-corporeal object. However, no statistically significant analgesic effect of vision of the virtual arm movement was found. The implications and limitations of this study are discussed.
It has been demonstrated that visual inputs can modulate pain. However, the influence of skin col... more It has been demonstrated that visual inputs can modulate pain. However, the influence of skin color on pain perception is unknown. Red skin is associated to inflamed, hot and more sensitive skin, while blue is associated to cyanotic, cold skin. We aimed to test whether the color of the skin would alter the heat pain threshold. To this end, we used an immersive virtual environment where we induced embodiment of a virtual arm that was co-located with the real one and seen from a first-person perspective. Virtual reality allowed us to dynamically modify the color of the skin of the virtual arm. In order to test pain threshold, increasing ramps of heat stimulation applied on the participants' arm were delivered con-comitantly with the gradual intensification of different colors on the embodied avatar's arm. We found that a reddened arm significantly decreased the pain threshold compared with normal and bluish skin.This effect was specific when red was seen on the arm, while seeing red in a spot outside the arm did not decrease pain threshold. These results demonstrate an influence of skin color on pain perception. This top-down modulation of pain through visual input suggests a potential use of embodied virtual bodies for pain therapy.
Despite the increasing interest in twin studies and the stunning amount of research on face recog... more Despite the increasing interest in twin studies and the stunning amount of research on face recognition, the ability of adult identical twins to discriminate their own faces from those of their co-twins has been scarcely investigated. One's own face is the most distinctive feature of the bodily self, and people typically show a clear advantage in recognizing their own face even more than other very familiar identities. Given the very high level of resemblance of their faces, monozygotic twins represent a unique model for exploring self-face processing. Herein we examined the ability of monozygotic twins to distinguish their own face from the face of their co-twin and of a highly familiar individual. Results show that twins equally recognize their own face and their twin's face. This lack of self-face advantage was negatively predicted by how much they felt physically similar to their co-twin and by their anxious or avoidant attachment style. We speculate that in monozygotic twins, the visual representation of the self-face overlaps with that of the co-twin. Thus, to distinguish the self from the co-twin, monozygotic twins have to rely much more than control participants on the multi-sensory integration processes upon which the sense of bodily self is based. Moreover, in keeping with the notion that attachment style influences perception of self and significant others, we propose that the observed self/co-twin confusion may depend upon insecure attachment.
Understanding the mental states of others entails a number of cognitive processes known as Theory... more Understanding the mental states of others entails a number of cognitive processes known as Theory of Mind (ToM). A relationship between ToM deficits and executive disorders has been hypothesized in individuals with Parkinson's disease (PD). The present study was aimed at investigating the effect of dysexecutive deficits on ToM abilities in PD patients without dementia. Participants included 30 PD patients and 30 healthy subjects (HC). PD patients were divided into two groups according to their executive test performance: patients with poor (dysexecutive group; n=15) and normal (executively unimpaired group; n=15) performance. All participants were administered faux pas recognition written stories. The dysexecutive PD patients performed less accurately than both HC and executively unimpaired PD individuals on all faux pas story questions (p< 0.05); the executively unimpaired PD group performed as accurately as the HC group on the ToM tasks. Results of the study clearly demonstrate that PD is not tout court associated with ToM impairments and that these may occur in PD patients as a function of the degree of their executive impairment. Our findings also indirectly confirm previous data on the role of the prefrontal regions in mediating ToM capacities.
Uploads
Papers by M. Martini