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Biomedical subjects

M E Ioffe

Publications and source records attributed to M E Ioffe.

At least 37 records · Page 2Linked to original sources
PubMed1981

[Postural support for local movements in cats and dogs].

A comparative analysis of adjustment of posture for performance of different kinds of local movements (movements elicited by electrical stimulation of the motor cortex; proprioceptive reaction of placing the paw on a support, conditioned lifts of the paw) was made in cats and dogs. The present experimental data were obtained in two laboratories independent of each other. For their quantitative analysis a number of criteria was elaborated which allow to obtain characteristics of the posture at concrete moments and differential characteristics based on the measurement of vertical forces of the limbs support. It was shown that the general characteristics of posture adjustment (the so called diagonal pattern) are identical in cats and dogs and in different kinds of movements; the degree of diagonality, however, depends considerably on the kind of movement. During conditioned movements the diagonality coefficient is higher in dogs than in cats.

Animals↗
PubMed1979

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.

Animals↗
PubMed1973

Supraspinal influences on spinal mechanisms activated prior to learned movement.

Dogs were trained to perform an instrumental avoidance reflex of lifting and holding a limb above a pre-determined level to prevent or to interrupt painful stimulation of the same limb. A tone preceding the stimulation by 0.5 s served as the CS. During the CS the excitability of the motoneuronal pools involved in the execution of the instrumental motor response was monitored as the magnitude of the response of knee flexors to single stimuli applied to sciatic nerve. For 70-80 ms preceding the onset of the EMG of the conditioned instrumental movement, the amplitude of the muscle response progressively increased. This phenomenon is apparently analogous to that of "motor presetting" described by others for man. Bilateral pyramidotomy at the medullary level was performed following the elaboration of instrumental reflexes. It produced obvious changes in the motor performance: the latencies of conditioned movements became longer and the speed of limb lifting decreased. It did not, however, alter the preparatory increase in motoneuronal excitability. On the other hand pyramidotomy prior to elaboration of the conditioned reflex strongly affected the preparatory changes, Destruction of the red nucleus contralateral to the conditioned limb in pyramidotomized dogs resulted in disappearance for 1.5 months of the conditioned motor response to the CS. After the response had been restored, the latency of movement showed a further increase, and the presetting of the spinal system was essentially absent.

Animals↗
PubMedDate not supplied

Mechanisms of motoric learning.

The basic principles of motoric learning are analyzed in this paper. Arguments are given for the position that instrumental conditioning is the basis for motoric learning, but that the mechanisms of insight as well as the system of foresight in analysis of the result also play a substantial role in it. The hypothesis is advanced, in comparing certain theories of learning, of the possibility of a synthetic approach. Two stages can be distinguished in the process of motoric learning, the formation of notional and coordinational programs. The formation and realization of learned movements which are antagonistic to the initial coordinations takes place under the constant control of the motor cortex, which effects the inhibition of interfering coordinations that develop in the course of learning.

Animals↗
PubMedDate not supplied

Certain methods of biomechanical description of various postural adjustment patterns during motoric learning in dogs.

Methods for the biomechanical description of spatial displacements of the center of mass of quadruped animal (dog), developed by the authors on the basis of an assessment of the vertical constituents of support pressures, as well as methods for the assessment of the postural adjustment pattern (coefficient of diagonality), are presented in this paper. The results are presented of an investigation of the role of the motor cortex in the accomplishment of the postural adjustment pattern of dogs, reorganized during learning, in the performance of an instrumental movement.

Animals↗
PubMedDate not supplied

Impairment of learning the voluntary control of posture in patients with cortical lesions of different locations: the cortical mechanisms of pose regulation.

The process of learning to produce voluntary changes in the position of the center of pressures using biological feedback was studied by stabilography in patients with hemipareses due to cerebrovascular lesions in the zone supplied by the middle cerebral artery. There were significant impairments to learning in all groups of patients, who had lesions in different sites, demonstrating that cortical mechanisms are involved in learning to control posture voluntarily. These studies showed that patients with lesions in the right hemisphere had rather greater deficits in performing the task than those with lesions in the left hemisphere. There were significant differences in the initial deficit in performing the task on the first day of training depending on the side of the lesion. All groups of patients differed from healthy subjects in that significant learning occurred only at the initial stages of training (the first five days). Learning at the initial stage in patients with concomitant lesions of the parietal-temporal area and with combined lesions with motor, premotor, and parietal-temporal involvement was significantly worse and the level of task performance at the end of the initial stage was significantly worse than in patient with local lesions of the motor cortex. The level of learning was independent of the severity of the motor deficit (paresis, spasticity), but was associated with the severity of impairment of the proprioceptive sense and the severity of disruption to the upright posture (asymmetry in the distribution of support pressures, amplitude of variation in the position of the center of pressures). The learning process had positive effects on the severity of motor impairment and on the asymmetry of the distribution of support pressures in the standing posture. Reorganization of posture during bodily movements occurred mainly because of impairment to the developed "non-use" stereotype of the paralyzed lower limb.

Biomechanical Phenomena↗
PubMedDate not supplied

Somatosensory evoked potentials during natural and learning rearrangements of posture accompanied by limb elevation in dogs.

Changes in the functional state of the sensorimotor cortex associated with reorganization of the natural pattern of postural rearrangement before limb elevation (the "diagonal" patten and of an artificial rearrangement (the "unilateral" pattern) were studied in dogs. The state of cortical structures on postural rearrangement was assessed in terms of the pattern of somatosensory evoked potentials produced in response to stimulation of the forelimb during postural preparation of the animal for elevating the hindlimb (acquired avoidance response to a sound signal). Evoked potentials during the natural postural preparation (the "diagonal" pattern) were compared with those during the altered pattern of postural preparation (the "unilateral" pattern), this preparation taking place prior to elevation of the limb. Controls consisted of evoked potentials in the resting state. Decreases were seen in the latencies and amplitudes of most components of evoked potentials during postural rearrangement. In general, changes in evoked potentials were less marked in the "unilateral" pattern than in the "diagonal" pattern, though the differences were significant only for the amplitude of the first negative component. Changes in evoked potentials were similar regardless of whether the supporting forces of the limb to which the test stimulus was applied increased or decreased during postural rearrangement. It is suggested that differences in evoked potentials may reflect changes in the interaction between neuronal populations within the sensorimotor cortex during reorganization of the pattern of postural rearrangement associated with learning.

Animals↗
PubMedDate not supplied

[Deficit of learning of posture voluntary control in patients with cortical lesions of various locations: cortical mechanisms of posture regulation].

Forty two hemiparetic patients after cerebrovascular accidents were trained to change the position of the center of pressure according to a target on the screen with the visual feedback control. The learning was substantially impaired in comparison with the group of healthy subjects. Patients with the right-hemispheric lesions showed somewhat greater learning deficit than patients with lesions in the left hemisphere. Lesion localization also affected the process of learning. The learning was disturbed to a greater extent in patients with lesions involving not only motor but also premotor and parietal cortical areas. In patients with parieto-temporal lesions the learning reached a very low level after three initial days of training, possibly, because of the deficit of sensory integration and of body scheme in the extra-personal space. Patients with combined lesions of the motor, premotor, and parietal areas showed the lowest results. The learning was shown to depend on the deficit of proprioception and extent of postural disturbances (asymmetry of body weight distribution and amplitude of the center of pressure oscillations) rather than on the extent of motor deficit (paresis and spasticity). However, the learning itself improved some motor disturbances.

Biofeedback, Psychology↗
PubMedDate not supplied

[Somatosensory evoked potentials during natural and learned patterns of postural adjustment, accompanying limb movements in dogs].

A goal of the study was to investigate cortical reorganization corresponding to inhibition of innate motor patterns during motor learning. Functional changes in the sensorimotor cortex during learned rearrangement of the natural diagonal pattern of postural adjustment (PA) accompanying a hindlimb movement into a new one, the so-called unilateral pattern, were studied in dogs by testing somatosensory evoked potentials (SEP) in response to stimulation of a forelimb during PA immediately before the limb movement onset. During PA the latency and the amplitude of several SEP components decreased. In general, changes in SEP were less pronounced in the learned unilateral pattern of postural adjustment in comparison with the innate diagonal pattern, but the difference was significant only for some SEP components. The SEP late positivity in the learned postural pattern was replaced by a negativity. The SEP changes were similar independently of whether the test stimulus was applied on the forelimb loaded or unloaded during postural adjustment. The data suggest that changes in interrelations between different neuronal populations in the sensorimotor cortex during formation and realization of a learned motor program can be reflected in SEP changes.

Animals↗
PubMedDate not supplied

[Nature of functional motor asymmetry in animals: state of the problem].

Handedness in skilled movements of animals is a result of interaction of innate motor preference and learning. The nature of the innate preference is not clear. Breeding of right-handed and left-handed mice revealed that the degree rather than direction of motor preference is an inherited feature. There is, however, a correlation between the direction of preference and a number of morphological, functional, and neurochemical characters. Shifts of a preference direction were found in some strains of mice. Differences between right-handed and left-handed rats were revealed in social behavior, learning, and resistance to forced retraining. Strains of rats with different forms of genetic epilepsy were characterized by the predominance of animals with a certain direction of the motor preference. This evidence suggests some genetic influence on a direction of the motor preference. Perhaps, genetic and environmental factors closely interact in determining motor preference in animals.

Animals↗
PubMedDate not supplied

[Neural basis of learning new movements: evolution of classical concepts].

According to classical consepts, the role of the motor cortex in performance of skilled movements of distal parts of extremities is confined to control of appropriate motoneurons by the "point-to-point" principle. However, much evidence of plasticity of the motor cortex and its active role in motor learning appeared in last decade. Fos-gene expression in the motor cortex was found to accompany learning a skill. Strengthening of horizontal pathways in layers II-III was revealed, and cholinergic input to tese layers was found to be important. The imaging data show that activity of the motor cortex increases during motor practice as well. This raises the question of specificity of the motor cortex in the motor learning per se. During acquisition of new movements some previously used synergies prevent the necessary coordination from being learned, so they must be suppressed in the process of motor learning. Investigations of central mechanisms of coordination interference in humans are still at the beginning. However, there are some animal models of reorganization and suppression of interfering synergies. The reorganization and suppression of coordination preventing realization of a new movement is shown to be a specific function of the motor cortex. After automation of new synergies the cortical control is still present, as distinct from the learned movements, which do not require suppression of interfering synergies. However, it does not mean that the conscious control of the performance is still present.

Brain↗
PubMedDate not supplied

[Features of learning voluntary control of posture after pyramidal and nigrostriatal lesions].

The study was aimed at investigation of a deficit of learning the center-of-pressure voluntary control in patients with lesions of corticospinal and nigrostriatal systems. Thirty three patients with Parkinson's disease and 20 patients with hemiparesis after cerebrovascular accidents in the MCA participated in the investigation. The subjects stood on a force platform and in the form of a computer game were trained to match the projection of the center of pressure (a cursor) with a target on the screen under the visual feedback control. Two different postural tasks were presented. In the first task the direction of the center-of-pressure shift was not known before, so the subject learned the general strategy of the center-pressure control. In the other task a precise postural coordination should be formed. The voluntary control of the center-of-pressure position was found to be impaired in both groups of patients. In the task of moving the center of pressure in various directions (general strategy), no differences in the initial deficit of the task performance were found between the groups, but the learning was more efficient in the group of hemiparetic patients. However, in the task with precise postural coordination, despite the greater initial deficit in the parkinsonian patients, the learning in this group of patients was substantially more efficient than in hemiparetic patients. The results suggest both common and different features of the involvement of the corticospinal and nigrostriatal systems in learning voluntary control of posture.

Aged↗
PubMedDate not supplied

[Effects of prefrontal ablations on the reaction of the active choice of feeder under different probability and value of the reinforcement on dog].

The role of the prefrontal cortex was investigated on the reaction of the active choice of the two feeders under changes value and probability reinforcement. The experiments were performed on 2 dogs with prefrontal ablation (g. proreus). Before the lesions the dogs were taught to receive food in two different feeders to conditioned stimuli with equally probable alimentary reinforcement. After ablation in the inter-trial intervals the dogs were running from the one feeder to another. In the answer to conditioned stimuli for many times the dogs choose the same feeder. The disturbance of the behavior after some times completely restored. In the experiments with competition of probability events and values of reinforcement the dogs chose the feeder with low-probability but better quality of reinforcement. In the experiments with equal value but different probability the intact dogs chose the feeder with higher probability. In our experiments the dogs with prefrontal lesions chose the each feeder equiprobably. Thus in condition of free behavior one of different functions of the prefrontal cortex is the reactions choose with more probability of reinforcement.

Animals↗