Are rotations in perceived visual vertical and body axis after stroke caused by the same mechanism?
OBJECTIVE
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 degrees 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 degrees +/-6 degrees overestimation and SVV 8.8 degrees +/-7.8 degrees toward the body). In patients, SVV (-4.4 degrees +/-4.6 degrees ) and LBA (-4.8 degrees +/-5.3 degrees ) were congruent in upright positions and when patients were ipsilesionally tilted (1.5 degrees +/-7 degrees and 1.9 degrees +/-7 degrees , respectively). In contrast, SVV and LBA were dissociated when the body was tilted to the contralesional side with overestimation of the LBA (-9.2 degrees +/-4.6 degrees ) but no effect on SVV (-4.1 degrees +/-6.4 degrees ).


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.
Barra
Julien
J
Laboratoire de Psychologie et NeuroCognition, Université Pierre Mendès France, Grenoble, France.
Benaim
Charles
C
Chauvineau
Valérie
V
Ohlmann
Théophile
T
Gresty
Michael
M
Pérennou
Dominic
D
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D011434:Proprioception / Q000502:physiology*; D012399:Rotation; D013028:Space Perception / Q000502:physiology*; D020521:Stroke / Q000503:physiopathology*; D014796:Visual Perception / Q000502:physiology*