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).