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We studied the extent to which automatic postural actions in standing human subjects are organized by a limited repertoire of central motor programs. Subjects stood on support surfaces of various lengths, which forced them to adopt different postural movement strategies to compensate for the same external perturbations. We assessed whether a continuum or a(More)
Freezing of gait (FoG) is a unique and disabling clinical phenomenon characterised by brief episodes of inability to step or by extremely short steps that typically occur on initiating gait or on turning while walking. Patients with FoG, which is a feature of parkinsonian syndromes, show variability in gait metrics between FoG episodes and a substantial(More)
Postural control is no longer considered simply a summation of static reflexes but, rather, a complex skill based on the interaction of dynamic sensorimotor processes. The two main functional goals of postural behaviour are postural orientation and postural equilibrium. Postural orientation involves the active alignment of the trunk and head with respect to(More)
This study examines the roles of somatosensory and vestibular information in the coordination of postural responses. The role of somatosensory information was examined by comparing postural responses of healthy control subjects prior to and following somatosensory loss due to hypoxic anesthesia of the feet and ankles. The role of vestibular information was(More)
Emergence of postural patterns as a function of vision and translation frequency. We examined the frequency characteristics of human postural coordination and the role of visual information in this coordination. Eight healthy adults maintained balance in stance during sinusoidal support surface translations (12 cm peak to peak) in the anterior-posterior(More)
Subjects with Parkinson's disease exhibit abnormally short compensatory steps in response to external postural perturbations. We examined whether: (1) Parkinson's disease subjects exhibit short compensatory steps due to abnormal central proprioceptive-motor integration, (2) this proprioceptive-motor deficit can be overcome by visual-motor neural circuits(More)
1. This study investigates the effects of parkinsonism and of dopamine replacement therapy (levodopa) on scaling the magnitude of automatic postural responses based on sensory feedback and on predictive central set. Surface reactive torques and electromyographic (EMG) activity in response to backward surface translations were compared in patients with(More)
The role of basal ganglia output via the globus pallidus (GP) was examined in monkeys trained to make rapid arm-reaching movements to a visual target in a reaction-time task. When neurons in the globus pallidus were destroyed by injection of kainic acid (KA) during task execution, contralateral arm movement times (MT) were increased significantly, with(More)
We tested whether human postural responses can be described in terms of feedback control gains, and whether these gains are scaled by the central nervous system to accommodate biomechanical constraints. A feedback control model can describe postural responses for a wide range of perturbations, but biomechanical constraints-such as on the torque that can be(More)