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Biomedical subjects

M E Ioffe

Publications and source records attributed to M E Ioffe.

At least 19 recordsLinked to original sources
PubMed2006

Involvement of the motor cortex in the bimanual unloading reaction: a transcranial magnetic stimulation study.

The responses of the biceps brachii muscle of the upper arm to magnetic stimulation of the motor cortex during the postural pretuning and forearm unloading tasks were studied in humans. On active unloading, the amplitude of the evoked response decreased in parallel with a decrease in muscle activity. During stationary holding of the load, the muscle response changed in proportion to the load. When, on the background of stationary holding of the load, the other arm took on the same load, the amplitude of the evoked response in the biceps muscle of the arm holding the load decreased without any change in the muscle activity. Passive unloading was accompanied by similar changes in the response evoked by magnetic stimulation as seen with active unloading. The question of whether the decrease in muscle activity (postural pretuning) in active unloading may be associated with both direct corticospinal influences and influences mediated via subcortical structures is discussed.

Evoked Potentials, Motor↗
PubMed2006

Recovery of a motor skill in rats with different forelimb preferences after lesioning of the caudate nucleus: the role of intense training.

The aim of the present work was to study the effects of training on the restoration of a lateralized motor skill (a food-procuring forelimb movement) in Wistar rats (n = 83) after lesioning of the caudate nucleus in conditions of infrequent testing and intensive retraining. On the basis of the training results, the rats were divided into those preferring the right (right-handers) or left (left-handers) limb. Testing was followed by lesioning of the head of the caudate nucleus on the side contralateral to the preferred paw. Animals with identical initial preferences were then divided into two groups: an infrequently tested group in which recovery of the skill was tested once weekly for five months, and an intensive retraining group, in which experiments were performed 3-4 times weekly, again for five months. After surgery, animals had to perform the food-procuring skill only with the "impaired" paw. Differences in the recovery of the skill were seen in animals with different limb preferences both in conditions of spontaneous recovery and in those recovering with training. Overall, animals with lesions of the left caudate nucleus (right-handers) showed better recovery than animals with lesions of the right caudate nucleus (left-handers) in both spontaneous recovery and in recovery with training. These findings suggest that the central neural mechanisms of recovery of a lateralized motor skill after unilateral lesioning of the caudate nucleus are different after lesions to the right and left hemispheres.

Animals↗
PubMed2005

Supervised learning of postural tasks in patients with poststroke hemiparesis, Parkinson's disease or cerebellar ataxia.

Supervised learning of different postural tasks in patients with lesions of the motor cortex or pyramidal system (poststroke hemiparesis: 20 patients), nigro-striatal system (Parkinson's disease: 33 patients) and cerebellum (spinocerebellar ataxia: 37 patients) was studied. A control group consisted of 13 healthy subjects. The subjects stood on a force platform and were trained to change the position of the center of pressure (CP) presented as a cursor on a monitor screen in front of the patient. Subjects were instructed to align the CP with the target and then move the target by shifting the CP in the indicated direction. Two different tasks were used. In "Balls", the target (a ball) position varied randomly, so the subject learned a general strategy of voluntary CP control. In "Bricks", the subject had to always move the target in a single direction (downward) from the top to the bottom of the screen, so that a precise postural coordination had to be learned. The training consisted of 10 sessions for each task. The number of correctly performed trials for a session (2 min for each task) was scored. The voluntary control of the CP position was initially impaired in all groups of patients in both tasks. In "Balls", there were no differences between the groups of the patients on the first day. The learning course was somewhat better in hemiparetic patients than in the other groups. In "Bricks", the initial deficit was greater in the groups of parkinsonian and cerebellar patients than in hemiparetic patients. However, learning was more efficient in parkinsonian than in hemiparetic and cerebellar patients. After 10 days of training, the hemiparetic and cerebellar patients completed the acquisition at a certain level whereas the parkinsonian patients showed the ability for further improvement. The results suggest that motor cortex, cerebellum, and basal ganglia are involved in voluntary control of posture and learning different postural tasks. However, these structures play different roles in postural control and learning: basal ganglia are mainly involved in learning a general strategy of CP control while the function of the motor cortex chiefly concerns learning a specific CP trajectory. The cerebellum is involved in both kinds of learning.

Adult↗
PubMed2005

The effects of the quality and probability of reinforcement on feeder selection by lobectomized dogs.

The role of the prefrontal cortex was studied in an active selection situation in which dogs had to choose one of two feeders, with changes in the quality and probability of the reinforcement provided in one of the feeders. The study was performed in two stages. Before surgery, animals were trained to place themselves on a start area during the interstimulus interval. Dogs were presented with a conditioned stimulus for investigation of the sequence of selection of feeders with identical reinforcements. After bilateral extirpation of the prefrontal areas (the proreal gyrus), dogs continuously ran from one feeder to the other during the interstimulus period. In response to the conditioned stimulus, the animals repeated the reaction of selecting the same feeder on many occasions during the first few (7-9) days. When there was a conflict between the probability and quality of reinforcement, the dogs came to prefer the feeder with the greater reinforcement quality despite its lower probability of presentation. In our experiments, operated animals presented with food at probabilities of 30% and 100% performed feeder selections with different probabilities. One of the functions of the prefrontal cortex in intact animals would appear to be to support the reaction of selecting the greater probability of reinforcement.

Animals↗
PubMed2004

Brain mechanisms for the formation of new movements during learning: the evolution of classical concepts.

Current concepts hold that the role of the motor cortex is limited to the control of the appropriate motoneurons on the "point-to-point" principle during the performance of specialized movements of the distal parts of the limbs. However, the last decade has seen the appearance of many data on the plasticity of the motor cortex and its active participation in the process of motor learning. Expression of fos genes has been observed in the motor cortex during the formation of specialized movements. Increases in intracortical horizontal connections in layers II-III during learning fine movements has been seen. The cholinergic input to layers II-III of the motor cortex plays a significant role in this. At the same time, data obtained by functional brain mapping have provided evidence that the activity of the motor cortex also increases during the practice of previously learned movements. This raises the question of the specific function of the motor cortex in the process of motor learning. During the formation of new movements during motor training, a number of previously used synergies interfere with the performance of newly formed coordinations and must be inhibited. The central mechanisms of interference of coordinations in humans have only just started to receive study. At the same time, there is an experimental model for the reorganization and inhibition of interfering synergies in animals. Reorganization of coordinations and inhibition of synergies interfering with the performance of a new movement have been shown to be a specific function of the motor area of the cortex. Cortical control persists during the automation of these synergies, which is not the case in other types of learned movements, though this in itself does not mean that conscious control of their performance also persists.

Animals↗
PubMed2004

Characteristics of learning voluntary control of posture in lesions of the pyramidal and nigrostriatal systems.

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.

Adult↗
PubMed2004

[Voluntary postural control learning with a use of visual bio-feedback in patients with spinocerebellar degenerations].

The study aimed at evaluation of possibility and features of voluntary postural control learning using biofeedback from a force platform in patients with spinocerebellar ataxias. Thirty-seven patients with different forms of spinocerebellar degenerations and 13 age-matched healthy subjects were trained to shift the center of pressure (CP) during several stabilographic computer games which tested an ability to learn 2 different types of voluntary postural control: general strategy and precise coordination of CP shifting. Despite the disturbances of static posture and ability for voluntary control of CP position, patients with spinocerebellar degenerations can learn to control a vertical posture using biofeedback on stabilogram. In contrast to healthy subjects, improvement of coordination in the training process does not exert a significant influence on the static posture characteristics, in particular on lateral CP oscillations. The results obtained suggest involvement of the cerebellum in both types of postural control that distinguishes them from pathology caused by motor cortex and nigro-striatal system involved only in one type of postural control.

Adolescent↗
PubMed2003

Specific functions of the motor cortex in reorganizing coordinations during motor training in animals and humans.

The involvement of the motor cortex in learning movements has recently attracted much attention. One aspect of motor learning is the inhibition of innate synergies which interfere with performance of the acquired movement. Various models of operant responses in dogs have demonstrated the critical role of the motor cortex in the reorganization and inhibition of interfering synergies during learning. The role of the motor cortex and corticospinal influences in the formation of new coordinations in humans was studied here in patients with organic lesions of the cerebral circulation involving the internal capsule, using postural coordination and movements in a bimanual unloading response as an example. Formation of the forearm stabilization response was deeply lesioned on the afflicted side. Some degree of impairment was also seen on the ipsilateral side, but it was no different from the level of learning impairment in patients with lesions not involving the internal capsule or in patients with parkinsonism. The existence of specific contralateral influences of the motor cortex and non-specific descending influences on the process of motor learning is proposed.

Aged↗
PubMed2001

[A specific function of the motor cortex in the reorganization of coordination in motor learning in animals and humans].

The findings suggest that a particular function of MCx in motor learning involves suppression of synergies and co-ordination which interferes with acquisition of new motor patterns. Experimental animal models based on inhibition of certain natural synergies or reflexes in the process of learning new co-ordination have been developed where the MCx is responsible for inhibition of natural motor patterns. Following the MCx lesion the natural synergies dominate again and the learned movement cannot be adequately performed. Similar disturbances occur after combined lesions of the premotor and parietal associative cortex or after lesions of the cerebellar nuclei. However, after the associative cortex or cerebellar lesions the recovery of learned co-ordinations is possible. This suggests the inhibition of inappropriate synergies or co-ordination during motor learning is a specific function of the MCx, the latter taking part in organisation of new co-ordination between posture and movement in humans as well.

Aged↗
PubMed2000

The use of neural transplantation for suppression of seizure activity in genetically epilepsy-prone rats.

The possibility of correcting seizure activity with neural transplantation was studied in Wistar rats with audiogenic seizures and in Krushinskii-Molodkina rats with high level of audiogenic seizures. In Wistar rats seizures were absent during 24 weeks after combined bilateral transplantation of striatal and cerebellar tissue from newborn rats into the parietal cortex. The same transplantation performed in Krushinskii--Molodkina rats increased the latency of audiogenic seizures. In some rats the intensity of seizures decreased, but they did not completely disappeared. Suppression of seizure activity in Krushinskii-Molodkina rats was observed after transplantation of striatal and cerebellar tissue simultaneously into the parietal cortex and inferior colliculi.

Animals↗
PubMed1999

Forearm postural control during unloading: anticipatory changes in elbow stiffness.

In this study, the equilibrium-point hypothesis of muscle-torque generation is used to evaluate the changes in central control parameters in the process of postural-maintenance learning. Muscle torque is described by a linear spring equation with modifiable stiffness, viscosity, and equilibrium angle. The stiffness is considered to be the estimation of the central command for antagonist-muscle coactivation and the equilibrium angle to be the estimation of the reciprocal command for a shift of invariant characteristics of the joint. In the experiments, a load applied to the forearm was released. The subjects were instructed to maintain their forearm in the initial horizontal position. Five sessions of approximately twenty trials each were carried out by eight subjects. During two "control" series, the load release was triggered by the experimenter. During three "learning" series, the load supported by one forearm was released by the subject's other hand. The elbow-joint angle, the angular acceleration, and the external load on the postural forearm were recorded. These recordings as well as anthropometric forearm characteristics were used to calculate the elbow-joint torque (which we called "experimental"). Linear regression analysis was performed to evaluate the equilibrium angle, joint stiffness, and viscosity at each trial. The "theoretical" torque was calculated using a linear spring equation with the found parameters. The good agreement observed between experimental and theoretical joint-torque time courses, apart from the very early period following unloading, argues in favor of the idea that the movement was mainly performed under a constant central command presetting the joint stiffness and the equilibrium angle. An overall increase in the stiffness occurred simultaneously with a decrease in the equilibrium angle during the "learning" series in all the subjects. This suggests that subjects learn to compensate for the disturbing effects of unloading by increasing the joint stiffness. The mechanism possibly responsible for the presetting of the central control parameters is discussed.

Cognition↗
PubMed1997

The ground reaction forces of postural adjustments during skilled reaching in unilateral dopamine-depleted hemiparkinson rats.

Rats with unilateral dopamine (DA) depletions (hemiParkinson analogue rats) produced by intracerebral 6-hydroxydopamine injection are impaired in using the contralateral (bad) limbs for postural adjustments. This article examines whether the bad limbs are impaired in applying the forces required to initiate postural adjustments that anticipate and accompany voluntary movements. The rats were trained to reach for food using their good paw while standing on small platforms, each of which measured force changes produced by an individual limb. In one condition the force platforms were aligned to support the limb placement of normal rats and in the second they were aligned to permit the DA-depleted rats to use a compensatory reaching stance. It was found that the bad limbs of the DA-depleted rats produced normal supporting reactions but did not initiate adjustments in posture. Postural adjustments were initiated with the good limbs and preceded rather than accompanied the reaching movements. When constrained to use the posture of normal rats, the DA-deplete rats could not reach successfully, but when allowed to adjust their stance to increase reliance on the good limbs, reaching performance improved. Measures of ground reaction forces confirm that DA-depleted rats can support posture but cannot initiate postural adjustments with their impaired limbs.

Adaptation, Physiological↗
PubMed1993

Differences in the recovery rate of a learned forelimb movement after ablation of the motor cortex in right and left hemisphere in white rats.

After ablation of the motor cortex contralateral to the preferred limb, rats were forced to use this limb in grasping food out of a horizontal tube by restraining the non-preferred foreleg with a bracelet. In a right-handed rat the motor behaviour is less impaired and the recovery is better after a left hemisphere lesion in comparison with a left-handed rat after a right hemisphere lesion. This difference is primarily the time needed to use the limb in reaching for seed (testperiod 3) and the total time needed for 10 successive seizings of seed (testperiod 5). Surprisingly, the differences in the course of recovery do not correlate with the degree of preoperative limb preference: the initially ambidextrous rate also show the same differences in results of the motor cortex ablation in left and right hemisphere. However, in the group of initially consistent ambidextrous rats, after 10 weeks of tests with a restrained forelimb, the testing under unrestrained free conditions shows a gradual decrease in the induced limb preference and a shift to the use of the foreleg contralateral to the intact hemisphere, while in contrast the initially consistent left- or right-handed rats preserve the limb preference under the unrestrained testing conditions. Therefore the degree of initial preference still influences the choice of limb after motor cortex ablation and intensive training to use the 'damaged' limb.

Animals↗
PubMed1991

Innate versus learned factors determining limb preference in the rat.

The basic factors determining forelimb preference in the performance of different skilled movements were studied in white rats. To analyse whether limb preference actually reflects an initial individual motor asymmetry or is a result of instrumental learning (the first successful movement becoming fixed), the method of retrograde amnesia from electroconvulsive shock was used. It was shown that limb preference is initial and not a results of learning and, evidently, is due to intrinsic factors. The preferred limb can be identified in as few as 3 successful movements. There is a gradation among animals according to the degree of initial limb preference and its resistance to rearrangement of the motor task. The differences of limb preference in different movements were also analysed. Dependence of the preference on the character of the required movement was shown. Four basic types of movement were revealed by factor analysis. As different muscular groups (distal and proximal), controlled by different descending motor systems can be involved in the performance of different movements, it is assumed that the initial motor asymmetry in each movement is a result of asymmetry of central motor structures involved in the realization of the movement. In the same animal asymmetry of different motor structures might be different. This could explain different limb preference in different movements.

Animals↗
PubMed1985

Analysis of vertical displacements of the center of gravity in the cat during limb flexion induced by cortical stimulation.

A limb movement and the associated postural adjustment result in a displacement of the center of gravity of the body. The vertical component of this displacement has been calculated from the variations in the sum of vertical forces at each limb. Through these variations, it is possible to measure the vertical acceleration of the center of gravity. Velocity and displacement are then obtained by two successive integrations of acceleration values. The magnitude of displacement of the center of gravity depends on the magnitude of limb displacement, and hindlimb flexion induces larger displacement than forelimb flexion. It is also directly linked to the time course of the vertical force variations recorded at each limb. The feed-forward character of the postural adjustment appears to minimize this amplitude, which leads us to discuss the functional significance of this postural adjustment.

Journal Article↗
PubMed1985

The learned rearrangement of an inborn postural pattern.

The postural displacement accompanying a learned movement was studied in the dog. Dogs were trained to change the diagonal postural pattern into an ipsilateral one. Such a rearrangement of inborn postural pattern is very difficult and requires several hundred trials. A biomechanical model connecting the changes of pressure of different limbs with kinematics of different part of the body is proposed.

Animals↗
PubMed1982

Biomechanical study of the mechanisms of postural adjustment accompanying learned and induced limb movements in cats and dogs.

Trajectories of the center of pressure and center of gravity projections were studied in dynamic conditions during learned movement and movement evoked by the motor cortex stimulation (induced movement) in dogs and cats. The learned movement began with initial displacement of the center of pressure towards the limb performing movement. It corresponded often with initial increasing of the performing limb pressure on support and it was a reason of initial acceleration of the center of gravity in the opposite direction. Induced movement began with decrease of the performing limb pressure on support. It could result in the initial displacement of the center of pressure in the wrong direction but usually it was corrected quickly and the general trajectories of the center of pressure and the center of gravity were similar to ones observed during learned movement. Results suggest different programs for movement and appropriate postural adjustment.

Animals↗