A lesion mapping study of anosognosia for contralesional hemiplegia in patients with right and left hemispheric lesions.

Anosognosia for hemiplegia (AHP) is defined as the total or partial lack of awareness about the own motor deficit contralateral to a brain lesion. According to the literature, this self-awareness deficit is mainly related to the right hemisphere functioning and concerns the left part of the body, even if some cases of AHP due to selective left-brain lesions have been described in the literature. It’s been hypothesized that the frequency of AHP due to left hemispheric lesions could have been underestimated since a left-brain lesion involves comprehensive and productive language deficits (aphasia), which makes more difficult, if not impossible, the assessment of the motor awareness deficit. Our study aims to verify the frequency of AHP in patients with left brain lesions and to compare the anatomical bases of anosognosia for hemiplegia in left and right brain-damaged patients using Voxel-Based Lesion Symptom Mapping (VLSM) analysis. Our study evaluated a cohort of 10 hemiplegic patients after a first focal stroke: five patients with unilateral right brain damage and five patients with unilateral left lesions. Based on the AHP assessment performed using Bisiach’s questionnaire and the VATAm test, we identified two anosognosic patients with unilateral right brain lesions. The lesion analysis showed that the two patients with AHP (patients P2 and P4) had a lesion in the classical regions associated with AHP, including the motor (BA4) and the premotor cortex (BA6) and the somatosensory area (BA3; Patient P2), the insular cortex, the basal ganglia (patient P4), confirming the anatomo-clinical association described in the literature. These results were also confirmed by the subtraction plots analysis between AHP and non-AHP patients. Unfortunately, considering the extremely small sample of the present study and the limited number of patients with AHP was not possible to conduct more in-depth and sophisticated lesion analyses. The main difference between the two groups lies in the extent of the lesions: indeed, RBD patients exhibited damage to extensive brain networks, while LBD patients had significantly more focal lesions. This is in accordance with the growing opinion that AHP is a multi-component network syndrome including different neuro-cognitive networks, suggesting that the presence of AHP is not merely dependent on a focal lesion in a specific brain area but requires damage to more extensive brain circuits and that different forms of AHP can be associated to discrete anatomical correlates. The present study also confirms the difficulty in studying populations of left-brain-injured patients with a lesion extension similar to that of the RBD patients and the need to develop motor awareness assessment procedures capable of bypassing the linguistic problems of these patients.