Unveiling covert disownership after stroke: a neuropsychological and neural approach.

Self-awareness can be impaired in different forms, including bodily features, following brain lesions. Such as other complex symptoms, these disorders seem not being localized in one brain area but may occur following the impairment of different parts of a network. One of the most disrupting body awareness disorder for people's functioning is the feeling that one or more body parts do not belong to the person anymore, the so-called 'body part disownership'. This symptom can be undetected, with recent findings suggesting that subtle signs of body disownership are revealed using an assessment with a non-verbal response, instead of a verbal interview. In the present study, by exploiting a large clinical dataset and state-of-the art analyses of lesion-induced disconnectivity, we have investigated this newly detected entity, called covert disownership, in the early phase post-stroke. 105 hospitalized stroke patients and 55 healthy controls were recruited over 2 years. Patients underwent a neurological and cognitive evaluation, including various measures of body ownership. We also assessed upper limb functions, using routine occupational therapy measures such as hand dexterity, strength, sensitivity and proprioception. To unveil its neural correlates, we ran innovative and robust region- and network-based lesion analyses. Our results indicate that about 30% of our sample exhibited covert disownership, involving either hands, arms, legs or face portions contralateral to the lesion, which affected the right- or the left-hemisphere. Lesion analyses confirmed the key role of structures such as the right insula, and basal ganglia, for upper limb ownership. Network-based structural connectivity data highlighted disconnections between temporo-occipital and parietal bilateral networks associated with disownership for the upper limb, as well as bilateral disconnections between fronto-basal and occipital parcels. Damage affecting the left superior longitudinal fasciculus was also linked to the right hand disownership. Altogether, we shed new light on the neural interconnections that, when perturbed, lead to body awareness disorders. Large-scale bilateral disconnections at the level of temporo-parietal and fronto-occipital networks explain covert disownership, with specific pathways as a function of the body part involved. We demonstrate that in the early phase of a brain damage this disorder may be underestimated but still affect patients' self-perception. This underscores the importance of sensitive tools to overcome the limitations of standard clinical examination, as well as of modelling brain damage in terms of networks rather than focal lesions. A better understanding of post-stroke disownership disorders may improve rehabilitation programs and predict optimal clinical outcome.