Brain Advance Access originally published online on August 4, 2008
Brain 2008 131(9):2401-2413; doi:10.1093/brain/awn170
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Lateropulsion, pushing and verticality perception in hemisphere stroke: a causal relationship?
1Clinique de Médecine Physique et Réadaptation, Hôpital Nord-CHU Grenoble, Université Grenoble 1°, 2Unité de Rééducation Neurologique du Grau du Roi, CHU Nîmes, France, 3Neuro-otology Unit, Division of Neuroscience and Mental health, Imperial College London, Charing Cross Hospital, Fulham Palace Road, 4Acute Stroke and Brain Injury Unit and 5Sobell Department of Neurophysiology, Institute of Neurology, The National Hospital for Neurology and Neurosurgery, Queen Square, London, UK
Correspondence to: Prof. D. A. Pérennou, Clinique de Médecine Physique et Réadaptation, Hôpital Nord-CHU BP 217 38043 Grenoble, Université Grenoble 1°, France E-mail: DPerennou{at}chu-grenoble.fr
The relationships between perception of verticality by different sensory modalities, lateropulsion and pushing behaviour and lesion location were investigated in 86 patients with a first stroke. Participants sat restrained in a drum-like framework facing along the axis of rotation. They gave estimates of their subjective postural vertical by signalling the point of feeling upright during slow drum rotation which tilted them rightwards–leftwards. The subjective visual vertical was indicated by setting a line to upright on a computer screen. The haptic vertical was assessed in darkness by manually setting a rod to the upright. Normal estimates ranged from –2.5° to 2.5° for visual vertical and postural vertical, and from –4.5° to 4.5° for haptic vertical. Of six patients with brainstem stroke and ipsilesional lateropulsion only one had an abnormal ipsilesional postural vertical tilt (6°); six had an ipsilesional visual vertical tilt (13 ±.4°); two had ipsilesional haptic vertical tilts of 6°. In 80 patients with a hemisphere stroke (35 with contralesional lateropulsion including 6 ‘pushers’), 34 had an abnormal contralesional postural vertical tilt (average –8.5 ± 4.7°), 44 had contralesional visual vertical tilts (average –7 ± 3.2°) and 26 patients had contralesional haptic vertical tilts (–7.8 ± 2.8°); none had ipsilesional haptic vertical or postural vertical tilts. Twenty-one (26%) showed no tilt of any modality, 41 (52%) one or two abnormal modality(ies) and 18 (22%) a transmodal contralesional tilt (i.e. PV + VV + HV). Postural vertical was more tilted in right than in left hemisphere strokes and specifically biased by damage to neural circuits centred around the primary somatosensory cortex and thalamus. This shows that thalamo-parietal projections have a functional role in the processing of the somaesthetic graviceptive information. Tilts of the postural vertical were more closely related to postural disorders than tilts of the visual vertical. All patients with a transmodal tilt showed a severe lateropulsion and 17/18 a right hemisphere stroke. This indicates that the right hemisphere plays a key role in the elaboration of an internal model of verticality, and in the control of body orientation with respect to gravity. Patients with a ‘pushing’ behaviour showed a transmodal tilt of verticality perception and a severe postural vertical tilt. We suggest that pushing is a postural behaviour that leads patients to align their erect posture with an erroneous reference of verticality.
Key Words: space representation; verticality perception; body orientation; lateropulsion; pushing; stroke
Abbreviations: RH, Right hemisphere; PV, postural vertical; HV, haptic vertical; VV, visual vertical; ipsilist, the patients with an ipsilesional lateropulsion; contralist, the patients with a contralesional lateropulsion; SCP, Scale for Contraversive Pushing; ANOVA, analysis of variance; PCA, principal component analysis
Received October 31, 2007. Revised June 16, 2008. Accepted July 2, 2008.
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