Bimanual non-congruent actions in motor neglect syndrome: A combined behavioral/fMRI study

In Motor Neglect (MN) syndrome, a specific impairment in non-congruent bimanual movements has been described. In the present case-control study, we investigated the neuro-functional correlates of this behavioral deficit. Two right-brain-damaged (RBD) patients, one with (MN+) and one without (MN−) MN, were evaluated by means of functional Magnetic Resonance Imaging (fMRI) in a bimanual Circles-Lines (CL) paradigm. Patients were requested to perform right-hand movements (lines-drawing) and, simultaneously, congruent (lines-drawing) or non-congruent (circles-drawing) left-hand movements. In the behavioral task, MN− patient showed a bimanual-coupling-effect, while MN+ patient did not. The fMRI study showed that in MN−, a fronto-parietal network, mainly involving the pre-supplementary motor area (pre-SMA) and the posterior parietal cortex (PPC), was significantly more active in non-congruent than in congruent conditions, as previously shown in healthy subjects. On the contrary, MN+ patient showed an opposite pattern of activation both in pre-SMA and in PPC. Within this fronto-parietal network, the pre-SMA is supposed to exert an inhibitory influence on the default coupling of homologous muscles, thus allowing the execution of non-congruent movements. In MN syndrome, the described abnormal pre-SMA activity supports the hypothesis that a failure to inhibit ipsilesional motor programs might determine a specific impairment of non-congruent movements

The anatomo-clinical picture of the pathological embodiment over someone else's body part after stroke

Recently, a monothematic delusion of body ownership due to brain damage (i.e., the embodiment of someone else's body part within the patient's sensorimotor system) has been extensively investigated. Here we aimed at defining in-depth the clinical features and the neural correlates of the delusion. Ninety-six stroke patients in a sub-acute or chronic phase of the illness were assessed with a full ad-hoc protocol to evaluate the embodiment of an alien arm under different conditions. A sub-group of seventy-five hemiplegic patients was also evaluated for the embodiment of the movements of the alien arm. Fifty-five patients were studied to identify the neural bases of the delusion by means of voxel-based lesion-symptom mapping approach. Our results show that, in forty percent of the whole sample, simply viewing the alien arm triggered the delusion, but only if it was a real human arm and that was seen from a 1st person perspective in an anatomically-correct position. In the hemiplegic sub-group, the presence of the embodiment of the alien arm was always accompanied by the embodiment of its passive and active movements. Furthermore, the delusion was significantly associated to primary proprioceptive deficits and to damages of the corona radiata and the superior longitudinal fasciculus. To conclude, we show that the pathological embodiment of an alien arm is well-characterized by recurrent and specific features and might be explained as a disconnection deficit, mainly involving white matter tracts. The proposed exhaustive protocol can be successfully employed to assess stroke-induced disorders of body awareness, unveiling even their more undetectable or covert clinical forms