A major problem for human standing posture is a high centre of gravity (COG) maintained over a relatively small base of support. The body, therefore, has a high potential energy, leading to priority of equilibrium control during almost all motor tasks including quiet standing. Research on postural control has focused mainly on two types of study. One type evaluates balance with respect to external conditions. Unexpected external disturbances reveal centrally programmed stereotyped postural responses. Afferent feedback also influences posture when the initial setting is disturbed. The second type evaluates postural adjustments to anticipated internal disturbances of balance and reveals feedforward postural adjustments (for review, see Oddson, 1990;Dietz, 1992). By feedforward, we mean that the controller predicts an external input or behaves using higherorder processing rather than simple negative feedback of a variable. Fewer studies have dealt with the problem of maintaining balance during quiet relaxed stance. Hellebrandt (1938) introduced the concept of the stretch reflex strategy, or 'geotropic reflex' where the shift of the COG constantly stimulated stretch afferents of postural muscles that then contracted reflexively. This strategy was questioned since the angular motion at the ankle was less than necessary to elicit a stretch reflex (Kelton & Wright, 1949). Subsequent studies supported a central organization of posture that did not regulate the ankle angle or muscle length but a more global parameter such as the position of the COG (Gurfinkel et al. 1980;Dietz, 1992). Thus, the system strategy replaced the stretch reflex strategy whose role was then limited to Journal of Physiology (1999) 1. We studied quiet stance investigating strategies for maintaining balance. Normal subjects stood with natural stance and with feet together, with eyes open or closed. Kinematic, kinetic and EMG data were evaluated and cross-correlated. 2. Cross-correlation analysis revealed a high, positive, zero-phased correlation between anteroposterior motions of the centre of gravity (COG) and centre of pressure (COP), head and COG, and between linear motions of the shoulder and knee in both sagittal and frontal planes. There was a moderate, negative, zero-phased correlation between the anteroposterior motion of COP and ankle angular motion. 3. Narrow stance width increased ankle angular motion, hip angular motion, mediolateral sway of the COG, and the correlation between linear motions of the shoulder and knee in the frontal plane. Correlations between COG and COP and linear motions of the shoulder and knee in the sagittal plane were decreased. The correlation between the hip angular sway in the sagittal and frontal planes was dependent on interaction between support and vision. 4. Low, significant positive correlations with time lags of the maximum of cross-correlation of 250-300 ms were found between the EMG activity of the lateral gastrocnemius muscle and anteroposterior motions of the COG and COP during normal stance. Narrow ...

A substantial body of work within the last decade has demonstrated that there is a variety of oscillatory phenomena that occur in the basal ganglia and in associated regions of the thalamus and cortex. Most of the earlier studies focused on recordings in rodents and primates. More recently, significant advances have been made in this field of research through the analysis of basal ganglia field potentials recorded from implanted deep brain stimulation electrodes in the basal ganglia of human patients with Parkinson's disease and other disorders. It now appears that oscillatory activity may play a significant role in the pathogenesis of these diseases. The most significant finding is that in Parkinson's disease synchronized oscillatory activity in the 10- to 35-Hz band (often termed "beta-band") is prevalent in the basal ganglia-thalamocortical circuits, and that such activity can be reduced by dopaminergic treatments. The entrainment of large portions of these circuits may disrupt information processing in them and may lead to parkinsonian akinesia (and perhaps tremor). Although less firmly established than the role of oscillations in movement disorders, oscillatory activities at higher frequencies may also be a component of normal basal ganglia physiology.

Buspirone may be effective in treating mild to moderate cerebellar ataxia. A double-blind study of the efficacy of buspirone in cerebellar ataxia is warranted.

We studied the postural stability of 23 canoeing and kayaking young athletes and 15 healthy untrained age matched subjects during quiet and sensory conflicted stance (standing on stable and foam support with open and closed eyes). We measured with a force platform the center of pressure excursions and applied mean sway amplitude (MA), mean sway velocity (SV) and their Romberg ratios, and sway dispersion index to evaluate standing balance. During standing with eyes open, the athletes in comparison to non-athletes showed in sagittal and frontal plane greater MA and SV when the support was stable and smaller MA and SV when it was unstable. During standing with eyes closed, there were no differences between groups when the support was stable, however, the athletes sway faster and have smaller MA than controls while standing on the foam support. During standing on stable support, Romberg ratios for MA and SV revealed that unlike non-athletes the athletes' MA and SV were vision independent. However, while standing on unstable support the athletes' MA and SV became vision dependent and even greater for the medio-lateral sway. Canoeists' SV vision dependency in both planes was greater than for other groups. These results are in line with our hypothesis that young kayaking and canoeing athletes have a different from non-athletes model of sensory integration due to their specific sporting activity. One possible mechanism of this model may be a subtle re-adaptation deficit after disembarking to stable ground with diminished sensitivity of vision and vestibular apparatus.