Body representations and brain damage

We review changes in body representation in patients with brain hemisphere damage and discuss their relationship with impaired limb movements in peripersonal space, navigation between objects/obstacles and control of the body's general posture and balance. The egocentric representation of the body's median sagittal axis (considered as the main zone around which movements are anchored) has been studied in most detail. This reference is distorted in patients with spatial neglect and involves a combination of ipsilesional translation and contralesional tilt. There are clear links with the patients' difficulties in egocentric tasks, activities of daily living and postural control. In both healthy subjects and patients, this reference axis can be modulated by somaesthetic, vestibular and visual stimulations; these phenomena have been used in rehabilitation programmes to reduce disease-induced deviations. A few studies have analyzed other lateral body reference (at the shoulders, in particular). These references were found to be more severely affected than the body midline (notably on the contralesional side). The severity of the distortion was related to the presence of lesions that mainly affected the parietal, somatosensory and multimodal association cortex (notably around the intraparietal sulcus) and, to a lesser extent, the middle temporal and frontal dorsolateral premotor cortex. These convergent results suggested that patients (notably those with neglect) have a complex distortion of the body schema and the perceptive representations of the body, that does not simply correspond to poor awareness of the contralateral hemicorpus.