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The aim of the study reported here was to investigate impairments on the learning of voluntary control of the center of pressures using visual feedback in patients with lesions of the corticospinal and nigrostriatal systems. Participants were 33 patients with Parkinson's disease and 20 patients with hemipareses due to circulatory lesions in the basin of the middle cerebral artery. Subjects stood on a stabilometric platform and used two computer games over 10 days to learn to shift the body relative to the foot to move the centre of pressures, indicated by the position of a cursor on the screen, with the target and to move the target to a specified part of the screen. The games differed in terms of the postural tasks. In one, the direction of movement of the center of pressures was not known to the subjects, and subjects learned a general strategy for posture control; the other formed a strictly defined postural coordination. Both groups of patients were found to have impairments of voluntary control of the position of the center of pressures. There were no differences between groups of patients, in terms of the severity of the initial performance deficit in the task involving shifts of the center of pressures in different directions (the general strategy for controlling the center of pressures), while learning of this task was more difficult for patients with Parkinson's disease. The initial deficit in the fine postural coordination task was more marked in patients with Parkinsonism, though learning in these patients was significantly better than in patients with hemipareses. It is suggested that the mechanisms of involvement of the nigrostriatal and corticospinal systems in learning the voluntary control of posture have elements in common as well as unique elements. [ABSTRACT FROM AUTHOR]

The capability for the unconscious control of the upright posture in elderly people is impaired, which increases the risk of falls and traumata. The impairment of the unconscious control of posture is partially compensated by the fixation of voluntary attention on the maintenance of an appropriate posture. Elderly people fall predominantly during the performance of movements that demand additional voluntary postural control, for example, unstable support conditions. Thus, voluntary postural control assumes importance in elderly persons. Since it is unclear whether this function changes with age, the aim of this work was to study age-related features of the learning voluntary postural control using visual feedback by center-of-pressure position. The results of the study showed that voluntary postural control is a complex multicomponent process that includes, at least, the following functions: selection of a strategy of postural control, its actualization, and precision of its regulation. With aging, strategy selection in healthy people impairs, but both elderly and middle-aged people can learn this function as successfully as the young. At the same time, despite the absence of an initial deficit in the accuracy of postural setting in elderly people, training of this function becomes substantially more difficult with age. [ABSTRACT FROM AUTHOR]

Characteristic features of upright posture maintenance and mechanisms of postural disorders in poststroke hemiparetic patients were studied using a bilateral force platform. The following features of postural disorders were revealed in the patients tested: an increase in the velocity and amplitude of the center-of-pressure (CP) sway as compared to in healthy subjects, an absolute decrease in the half-cycles of the CP sway, asymmetry of weight bearing by both feet, and a shift of the center of pressure of an affected foot towards the toe. The disturbance of stability of the vertical posture in such patients is to a greater extent associated with weight-bearing asymmetry. It was shown that the character of the CP sway is mainly determined by a disorder of the sensory motor control, whereas damage to the efferent pathways is responsible for the postural asymmetry. Increase in the muscle tone restricts the sway amplitude. Thus, several forms of postural instability are characteristic of hemiparetic patients. Predominantly sensory, motor, or tonic disorders are responsible for these disturbances of stability. [ABSTRACT FROM AUTHOR]