The polymodal sensory cortex is crucial for controlling lateral postural stability: evidence from stroke patients.

In modern literature, internal models are considered as a general neural process for resolving sensory ambiguities, synthesising information from disparate sensory modalities, and combining efferent and afferent information. The polymodal sensory cortex, especially the temporoparietal junction (TPJ), is thought to be a nodal point of the network underlying these properties. According to this view, a pronounced disruption of the TPJ functioning should dramatically impair body balance. Surprisingly, little attention has been paid to this possible relationship, which was the subject of investigation in this study. Twenty-two brain-damaged patients and 14 healthy subjects were subjected to a self-regulated lateral balance task, performed while sitting for 8 s on a rocking platform. Their lateral body balance was analysed both with and without vision (darkness). Support displacements in the frontal plane were recorded by means of an accelerometer. Two criteria were taken into account to evaluate body stability in each trial: the number of aborted trials due to balance loss and the angular dispersion of the supporting surface. Lesions involving the temporoparietal junction were found to markedly increase body instability, both with and without vision. Therefore, the temporoparietal junction plays a pivotal role in lateral body stabilisation, irrespective of the sensory condition in which the task is performed. This suggests that body stability is controlled throughout internal model(s).

[Postural balance following stroke: towards a disadvantage of the right brain-damaged hemisphere]. / Posture et équilibre après accident vasculaire cérébral: désavantage de l'hémisphère droit.

In the light of studies published in the last ten years, we have suspected a differential influence of the sides of hemispheric cerebral lesions on posture and balance. A study was aimed at verifying this hypothesis, the method of which being original because many possible confounding factors such as age, sex as well as topography and size of the brain lesion have been taken into account in the statistical analysis. Inclusion criteria were: right-handed patients, first stroke, no previous disease which might have affected balance. Their postural abilities (ranging from 0 to 36) were assessed 90 +/- 3 days after stroke onset on a clinical scale. This clinical assessment was used here because it could be easily performed in all patients, irrespective of the severity of their impairment. Lesion locations were determined using the Atlas by Talairach and Tournoux and the number of cerebral areas altered gave an estimation of the lesion size. The first fifty patients consecutively admitted to rehabilitation and responding to the inclusion criteria were thus examined (25 with a right and 25 with a left hemispheric lesion; 14 women and 36 men; mean age 57.2 = yrs). The main result was lower postural performances in right brain-damaged patients than in left brain damaged patients (21.5 vs 29.4; p = 0.01). Postural abilities were also inversely related to age (r = -0.28; p = 0.04), lesion size (r = -0.41; p = 0.003) and were lower in women than in men (22.1 vs 28.8; p = 0.02). This study therefore confirms the existence of a right hemispheric dominance for postural control. The existence of inverse correlation between postural abilities and the number of omitted targets in cancellation task on one hand (r = -0.63, p < 0.001), the ipsilesional bias in line bissection on the other hand (r = -0.36; p = 0.01), argued for a relationship between the main result of this study and the well known cerebral organization of spatial information processing, based on a right hemisphere dominance for spatial attention and/or representation. The 'postural neglect' concept is discussed.