No abstract

In two experiments we explore the structure of complex sequences of drawing movements. We find that in these movements a single parameter--the velocity gain factor--relates the geometrical and kinematic aspects of the movement trajectory via a two-thirds power law. In Experiment 1 we investigate the relation between the velocity gain factor and the linear extent of the trajectory. In Experiment 2 we demonstrate that the gain factor provides a criterion for segmenting the movement into distinct units of motor action, and we investigate the effects of the speed of execution on this segmentation. A theoretical analysis shows that the results of both Experiments 1 and 2 can be given a unitary interpretation by assuming a coupling function of variable strength between segments. The general problem of representing motor programs is discussed within this theoretical framework.

Gamma knife surgery was effective in controlling the growth of residual NPA after previously performed maximal surgical debulking. The major advantage of GKS compared with fractionated radiotherapy seems to be a lower risk of side effects, especially a lower risk of hypopituitarism.

Our results indicate that structural alterations of small cerebral vessels are present in hypertensive patients compared with normotensive individuals, similar to those previously observed in subcutaneous small arteries.

The clinical state before treatment is certainly relevant in predicting outcome. Age and duration of the symptoms before treatment have no direct relation to the chances of improvement with treatment, particularly when motor improvement is considered. The modality of onset of symptoms and location of the fistula play significant roles, also: a fistula in the lower thoracic segment was associated with more severe symptoms but tended to improve more (83%, P = 0.04) after treatment. Midthoracic and lumbar fistulae showed a lower incidence of improvement (<50%).