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(Stroke. 2008;39:3099.)
© 2008 American Heart Association, Inc.

Research Letters

Are Rotations in Perceived Visual Vertical and Body Axis After Stroke Caused by the Same Mechanism?

Julien Barra, PhD; Charles Benaim, MD, PhD; Valérie Chauvineau, MD; Théophile Ohlmann, PhD; Michael Gresty, PhD Dominic Pérennou, MD, PhD

From the Laboratoire de Psychologie et NeuroCognition (J.B., T.O.), Université Pierre Mendès France, Grenoble, France; Clinique de MPR-CHU et Université Joseph Fourrier (J.B., V.C., D.P.), Grenoble, France; Service de Rééducation Neurologique (C.B., D.P.), CHU Dijon, France; and the Divisions of Neuroscience & Mental Health (M.G.), Imperial College London, London, UK.

Correspondence to Dominic Pérennou, MD, PhD, Clinique MRP-CHU, BP217 38043 Grenoble cedex, France. E-mail DPerennou{at}chu-grenoble.fr

Background and Purpose— The aim of this study was to investigate whether allocentric and egocentric coordinate systems are congruently biased after hemisphere stroke, which would suggest a single underlying mechanism.

Methods— The perception of the long body axis (LBA), an egocentric reference, and that of the subjective visual vertical (SVV), an allocentric reference, was assessed in both the upright position and with 30° lateral body tilts in 15 patients with a hemisphere stroke and 12 control subjects.

Results— In control subjects, estimates were accurate in upright but rotated in tilted positions (LBA 7°±6° overestimation and SVV 8.8°±7.8° toward the body). In patients, SVV (–4.4°±4.6°) and LBA (–4.8°±5.3°) were congruent in upright positions and when patients were ipsilesionally tilted (1.5°±7° and 1.9°±7°, respectively). In contrast, SVV and LBA were dissociated when the body was tilted to the contralesional side with overestimation of the LBA (–9.2°±4.6°) but no effect on SVV (–4.1°±6.4°).

Conclusions— Because rotations in egocentric and allocentric reference systems found after stroke are differently modulated by lateral tilts, they are not due to a single underlying mechanism. However, they share common bases and can be simultaneously reduced by ipsilesional body tilt. Differences in the way somesthetic information is integrated may explain the differences in LBA and SVV.

Key Words: longitudinal body axis • pushing • spatial representation • stroke • subjective visual vertical

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