Functional contribution of brain regions in a body-ownership illusion: A lesion study

Abstract

The feeling of ownership of our limbs is a fundamental aspect of self-consciousness. This experience can be experimentally manipulated by a paradigm based on intersensory correlations. Subjects may acquire feelings of body-ownership of a rubber hand placed in front of them, if the viewed rubber hand and the subject's covered own hand are repeatedly stricken simultaneously. In a previous functional imaging study this “rubber hand illusion“ (RHI) was associated with activity in bilateral premotor, contralateral parietal and cerebellar areas, but which of these activations was essential to the perceptual experience remained unknown. It is also unknown whether RHI is correlated with a disturbance of the primary perceptual experience of body-ownership. To address these questions we correlated the ability to elicit a RHI with lesion location in 60 acute stroke patients. Lesion analysis was performed on diffusion weighted MR imaging using freely available software tools. The presence of anosognosia and asomatognosia was also assessed. RHI was also tested in 120 healthy controls of different age. Ischemic lesions in each patient's diffusion-weighted MRI scan were marked manually as regions of interest (ROI) and transformed to the structural standard space of the MNI152 template by full affine registartion. Right-hemispheric lesions were mirrored across the midline. We used subtraction analysis to outline regions which might be essential for the RHI. In the control group, the illusion occurred in 86% on both sides, in 12% only on one side. There were no significant effects of age, body side or handedness with regard to the probability to elicit a RHI. Of 60 patients, RHI could not be elicited exclusively contralesionally in 8 (13%), and bilaterally in 7 (12%) patients. Loss of RHI did not correlate with asomatognosia or anosognosia. Unilateral loss of RHI was associated with enhanced lesion probability in caudal basal ganglia and in parietal regions while bilateral loss of RHI was associated with enhanced lesion probability in caput of the caudate nucleus, the insula and subcortical regions bordering the premotor area. The results are compatible with a role for premotor area and its connections for generation of the RHI. Because impairment of RHI did not correlate with disturbance of elementary perceptual experience of body ownership different brain regions may contribute to these perceptual experiences.