title: When your arm becomes mine: pathological embodiment of alien limbs using tools modulates own body representation.
abstract: Previous evidence has shown that active tool-use can reshape one's own body schema, extend peripersonal space and modulate the representation of related body parts. Here we investigate the effect of tool-use training on length representation of the contralesional forearm in brain-damaged hemiplegic patients who manifested a pathological embodiment of other people body parts. Four patients and 20 aged-matched healthy-controls were asked to estimate the mid-point of their contralesional forearm before and after 15 min of tool-use training (i.e. retrieving targets with a garbage plier). In the case of patients, training was always performed by the examiner's (alien) arm acting in two different positions, aligned (where the pathological embodiment occurs; E+ condition) or misaligned (where the pathological embodiment does not occur; E- condition) relative to the patients' shoulder. Healthy controls performed tool-use training either with their own arm (action condition) or observing the examiner's arm performing the task (observation condition), handling (observation with-tool condition) or not (observation without-tool condition) a similar tool. Crucially, in the E+ condition, when patients were convinced to perform the tool-use training with their own paralyzed arm, a significant overestimation effect was found (as in the Action condition with normal subjects): patients mislocated their forearm midpoint more proximally to the hand in the post- than in the pre-training phase. Conversely, in the E- condition, they did not show any overestimation effect, similarly to healthy subjects in the observation condition (neither in the with-tool nor in the without-tool condition significant overestimation effects were found). These findings show the existence of a tight link between spatial, motor and bodily representations and provide strong evidence that a pathological sense of body ownership can extend to intentional motor processes and modulate the sensory map of action-related body parts.
authors.affiliation: SAMBA (SpAtial, Motor & Bodily Awareness) Research Group, Department of Psychology, University of Torino, 10123 Torino, Italy; San Camillo Hospital of Torino, 10152 Torino, Italy. Electronic address: fra.garbarini@gmail.com.
authors.forename: Francesca
authors.initials: F
authors.lastname: Garbarini
authors.affiliation: SAMBA (SpAtial, Motor & Bodily Awareness) Research Group, Department of Psychology, University of Torino, 10123 Torino, Italy.
authors.forename: Carlotta
authors.initials: C
authors.lastname: Fossataro
authors.affiliation: SAMBA (SpAtial, Motor & Bodily Awareness) Research Group, Department of Psychology, University of Torino, 10123 Torino, Italy; Neuroscience Institute of Torino (NIT), University of Torino, 10126 Torino, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Berti
authors.affiliation: SAMBA (SpAtial, Motor & Bodily Awareness) Research Group, Department of Psychology, University of Torino, 10123 Torino, Italy; San Camillo Hospital of Torino, 10152 Torino, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Gindri
authors.affiliation: Department of Psychology, University of Milano-Bicocca, 20126 Milano, Italy; NeuroMi - Milan Center for Neuroscience, University of Milano-Bicocca, 20126 Milano, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Romano
authors.affiliation: SAMBA (SpAtial, Motor & Bodily Awareness) Research Group, Department of Psychology, University of Torino, 10123 Torino, Italy; Neuroscience Institute of Torino (NIT), University of Torino, 10126 Torino, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Pia
authors.affiliation: Department of Philosophy, University of Milan, 20122 Milano, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: della Gatta
authors.affiliation: Department of Psychology, University of Milano-Bicocca, 20126 Milano, Italy; NeuroMi - Milan Center for Neuroscience, University of Milano-Bicocca, 20126 Milano, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Maravita
authors.affiliation: SAMBA (SpAtial, Motor & Bodily Awareness) Research Group, Department of Psychology, University of Torino, 10123 Torino, Italy; Neuroscience Institute of Torino (NIT), University of Torino, 10126 Torino, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Neppi-Modona
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001132:Arm / Q000502:physiology*; D001828:Body Image; D001930:Brain Injuries / Q000150:complications; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006429:Hemiplegia / Q000209:etiology; D018594:Human Body; D006801:Humans; D008297:Male; D008609:Mental Status Schedule; D008875:Middle Aged; D009483:Neuropsychological Tests; D010468:Perceptual Disorders / Q000209:etiology; D011597:Psychomotor Performance / Q000502:physiology*; D013028:Space Perception / Q000502:physiology*
keywords: Action observation; Body metric representation; Brain-damaged patients; Embodiment; Peripersonal space re-mapping; Tool-use training