Biased postural vertical in humans with hemispheric cerebral lesions.

This study was aimed at demonstrating the existence of a biased postural vertical in humans with a recent cerebral lesion. The postural vertical of patients and controls was analysed comparatively using a self-regulated balancing task, performed in sitting posture. Patients displayed a quite constant (19/22) contralesional tilt of the postural vertical (mean -2.6 degrees), varying with the severity of their spatial neglect and hemianaethesia. Eight of them showed a pathological contralesional bias (mean -5.5 degrees) as compared to normals. This result indicates an asymmetric process of somatic graviceptive information due to some cerebral lesions. When patients were subjected to a transcutaneous electrical stimulation applied onto the contralesional side of the neck, body verticality was especially improved in those who showed a pathological bias in the postural vertical. This effect could thus be due to a reduced distortion in the egocentric co-ordinate system for spatial information processing.