[Impairment of the accuracy of tracking movements in lesions of the cerebellum and pyramidal system in man]. / Narusheniia tochnostnykh slediashchikh dvizhenii pri porazhenii mozzhechka i piramidnoi sistemy u cheloveka.

Kinematic and electromyographic characteristics of step-tracking movements performed with and without visual guidance have been studied in 3 groups of patients suffering from hereditary lesions of intermedial and lateral systems of the cerebellum and pyramidal tract. Lesions of the intermedial cerebellum not changing parameters of the first preprogrammed component altered deeply the maintenance phase that was performed as large oscillations around a required level. Lesions of the lateral cerebellum, on the contrary, were followed by inability to control accurately the amplitude of steps which were performed with a constant hypermetric error; the maintenance phase of movement was not disturbed in this group. In patients suffering from pyramidal lesions the initial rapid limb position adjustment was replaced by slow approximating tracking; the maintenance component of the movement was performed with fluctuations and constant drift towards the ground. It is concluded that whereas the lateral cerebellar system is involved in central motor program mechanisms, the intermedial cerebellum is essential for accurate postural maintenance.

[Characteristics of program-type movements in lesions of various cerebellar systems in man]. / Kharakteristiki dvizhenii programmnogo tipa pri porazhenii razlichnykh sistem mozzhechka u cheloveka.

Mechanisms of participation of two main cerebellar systems, i.e. lateral and intermedial ones, in control of preprogrammed voluntary movements have been studied in man. Related movements were analyzed in healthy subjects and in groups of patients suffering from different forms of cerebellar and pyramidal disorders. The task consisted of series of dorsal or plantar flexions of foot of increasing amplitudes with minimal amplitude of neighbouring movements. It was shown that both the lateral and intermedial cerebellar lesions were followed by deep alterations in program motor control mechanisms, however the intensity and specific features of alterations in two groups under study differed significantly. In patients suffering from pyramidal lesions the ability to perform programmed movements was lost completely.

[A wave nature of the central regulation of the trajectory of the articular angle in man]. / O volnovoi prirode tsentral'nogo protsessa formirovaniia traektorii izmeneniia sustavnogo ugla u cheloveka.

It is supposed that muscles of a single joint are controlled by a wave propagation of excitation along a central line-ordered neuronal ensemble. The number of steady active output ensemble neurons increases with wave-front displacement and the neurons discretely contribute to the motor command that is defined in terms of shifts of the so-called invariant muscle force-length characteristics. The terminal position of the wave front is responsible for the final angular limb position, whereas the wave velocity responsible for the peak movement speed. To verify the wave model, human time-angle trajectories of rapid arm movements to different positions in the horizontal plane were analysed. The trajectories fall into groups having the following properties: 1) The initial profiles of the trajectories that belong to one group are identical; 2) the duration of the coincidence of any two grouped trajectories increases with their extent; 3) summation of two or more grouped trajectories with a certain time delay between them again gives a trajectory which belongs to the same group. The data obtained are in good agreement with the wave model.

On the functions of the cortical motor area in precise movement organization.

The effects of unilateral ablation of the cortical motor forelimb area on instrumental avoidance responses consisting of lifting the forelimb and holding it within a 4 cm wide "safety zone" were studied in dogs. It was found that the surgery irreversibly impaired the search for the safety zone, while the ability to maintain the limb at a certain height was not affected. The surgery also impaired the corrective movements, especially if their direction was opposite to the inborn unconditioned reaction. The ability to perform corrective movements of small amplitude was also transiently diminished Widening of the safety zone markedly improved the post-operative performance.

[Specificity of nuclear elements of the motor region of the cortex in organizing a precise motor response]. / O spetsifike iadernykh élementov motornoi oblasti kory v organizatsii tochnostnoi dvigatel'noi reaktsii.

After elaboration and consolidation of precise instrumental avoidance reflexes in dogs (lifting of a fore-leg to a 4-centimeters wide "safety zone"), a part of motor cortex in the area of moving leg was ablated. After the operation the search for "safety zone" i. e. the precision of estimating the position of the leg was irreversibly impaired, but the animal was still able to hold its extremity at the same level for a long period of time. Artifically elaborated motor coordination--antagonistic to the innate one--also showed irreversible impairment. However, in case of an extremely "drilled" reaction (5.000 pairings) the elaborated coordination persisted. Minimal amplitude of correction movements increased too (i. e. subtlety of movements decreased), but during retraining this parameter of the movement became compensated. The data obtained suggest that the specificity of central cellular elements of the cortical motor area consists in estimation of extremity position which is necessary for finding a given point in space.