Defective reproduction of passive meaningless gestures in right brain damage: a perceptual disorder of one's own body knowledge?

Right Hemisphere Damaged Patients (RHDP) with left hemiparesis are known to experience motor programming difficulties and to have poorer functional outcome when compared with Left Hemisphere Damaged Patients (LHDP). The role played by body-related cognitive disorders remains unclear. In this study we investigate whether reproduction of passive meaningless gestures may contribute to a further development of this question. Ten RHDP with neglect, 10 RHDP without neglect, 10 LHDP, and 10 controls were given a battery of tasks requiring reproduction of passive meaningless gestures. The gestures were passively applied by the examiner on either the ipsilesional or the contralesional upper limb of the subject who was asked to reproduce them with his ipsilesional- non-paretic -limb. LHDP performed virtually as well as controls when the influence of deafferentation was controlled. The performance of RHDP with and without neglect did not differ from each other but both groups were significantly impaired when compared with either controls or LHDP, whether the gestures were applied on the contralesional or ipsilesional limb. RHDP performed defectively whether they had closed or open eyes, which tends to indicate a perceptual multimodal integration disorder rather than a modality-related sensory disorder. The left hemisphere is generally considered dominant for deliberate motor control of both sides of the body, not only for symbolic gestures but also for (visual) imitation of meaningless gestures. The results of this study raise the question of why reproduction of meaningless gestures is more impaired for LHDP than RHDP when stimulus presentation is visual and vice versa when stimulation is passively applied upon the subject's body. One reason may be that in visual imitation, the model is given by another person's body, whereas passive gestures, directly applied upon one's body, place demands on perceptual analysis of one's own body experience. These results might give evidence for a disorder of bilateral, perceptual, multimodal integration of knowledge about one's own body in RHDP.