Abstract
Brain damage may induce a dysfunction of upright body position termed “pusher syndrome”. Patients with such disorder suffer from an alteration of their sense of body verticality. They experience their body as oriented upright when actually tilted nearly 20 degrees to the ipsilesional side. Pusher syndrome typically is associated with posterior thalamic stroke; less frequently with extra-thalamic lesions. This argued for a fundamental role of these structures in our control of upright body posture. Here we investigated whether such patients may show additional functional or metabolic abnormalities outside the areas of brain lesion. We investigated 19 stroke patients with thalamic or with extra-thalamic lesions showing versus not showing misperception of body orientation. We measured fluid-attenuated inversion-recovery (FLAIR) imaging, diffusion-weighted imaging (DWI), and perfusion-weighted imaging (PWI). This allowed us to determine the structural damage as well as to identify the malperfused but structural intact tissue. Pusher patients with thalamic lesions did not show dysfunctional brain areas in addition to the ones found to be structurally damaged. In the pusher patients with extra-thalamic lesions, the thalamus was neither structurally damaged nor malperfused. Rather, these patients showed small regions of abnormal perfusion in the structurally intact inferior frontal gyrus, middle temporal gyrus, inferior parietal lobule, and parietal white matter. The results indicate that these extra-thalamic brain areas contribute to the network controlling upright body posture. The data also suggest that damage of the neural tissue in the posterior thalamus itself rather than additional malperfusion in distant cortical areas is associated with pusher syndrome. Hence, it seems as if the normal functioning of both extra-thalamic as well as posterior thalamic structures is integral to perceiving gravity and controlling upright body orientation in humans.
Highlights
Human species is the only obligate biped among primates
While TTP is a parameter that depicts the arrival time of blood in the brain tissue, maximal signal reduction (MSR) measures the amount of blood flow reaching the different regions of the brain and is closely related to relative cerebral blood flow in stroke patients [43,44]
By using the anatomical parcellation of the MNI single-subject brain by Tzourio-Mazoyer et al [45] implemented in MRIcron software [33] and the Julich probabilistic cytoarchitectonic atlas for the white matter fiber tracts [46,47], we found the center of lesion overlap for the patients with pusher syndrome affecting the insula, frontal and rolandic operculum, inferior frontal gyrus, pre- and postcentral gyri, as well as part of the corticospinal tract, inferior occipitofrontal and uncinate fasciculi
Summary
Human species is the only obligate biped among primates. Our brain has become remarkably efficient in stabilizing the upright body position in space. The perception of our body orientation is achieved by the convergence of inputs from multiple sources, including vestibular, visual, and somatosensory information [1]. When these sensory channels work properly, their inputs and their integration indicate verticality in a congruent manner. Damage to this system causes diverse disorders of posture and of balance control [2,3,4,5,6,7]. A very intriguing and severe disorder of upright body position is the ‘‘pusher syndrome’’ A very intriguing and severe disorder of upright body position is the ‘‘pusher syndrome’’ (for review ref. [8])
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