Vestibular signal processing in a subject with somatosensory deafferentation: The case of sitting posture

Jean Blouin¹ , Normand Teasdale²^,3 and Laurence Mouchnino¹

¹Laboratoire de Neurobiologie de la Cognition, CNRS and Aix Marseille Université, 3 Place Victor Hugo, 13331 Marseille, France

²Faculté de Médecine, Division de kinésiologie, Université Laval, Québec, Canada

³Centre de recherche du CHA et Centre d'excellence sur le vieillissement, Hôpital Saint-Sacrement, Québec

author email corresponding author email

BMC Neurology 2007, 7:25doi:10.1186/1471-2377-7-25


Published:	29 August 2007

Abstract

Background

The vestibular system of the inner ear provides information about head translation/rotation in space and about the orientation of the head with respect to the gravitoinertial vector. It also largely contributes to the control of posture through vestibulospinal pathways. Testing an individual severely deprived of somatosensory information below the nose, we investigated if equilibrium can be maintained while seated on the sole basis of this information.

Results

Although she was unstable, the deafferented subject (DS) was able to remain seated with the eyes closed in the absence of feet, arm and back supports. However, with the head unconsciously rotated towards the left or right shoulder, the DS's instability markedly increased. Small electrical stimulations of the vestibular apparatus produced large body tilts in the DS contrary to control subjects who did not show clear postural responses to the stimulations.

Conclusion

The results of the present experiment show that in the lack of vision and somatosensory information, vestibular signal processing allows the maintenance of an active sitting posture (i.e. without back or side rests). When head orientation changes with respect to the trunk, in the absence of vision, the lack of cervical information prevents the transformation of the head-centered vestibular information into a trunk-centered frame of reference of body motion. For the normal subjects, this latter frame of reference enables proper postural adjustments through vestibular signal processing, irrespectively of the orientation of the head with respect to the trunk.