Prior history of FDI muscle contraction: different effect on MEP amplitude and muscle activity.

Motor evoked potentials (MEPs) in the right first dorsal interosseous (FDI) muscle elicited by transcranial magnetic stimulation of left motor cortex were assessed in ten healthy subjects during maintenance of a fixed FDI contraction level. Subjects maintained an integrated EMG (IEMG) level with visual feedback and reproduced this level by memory afterwards in the following tasks: stationary FDI muscle contraction at the level of 40 ± 5 % of its maximum voluntary contraction (MVC; 40 % task), at the level of 20 ± 5 % MVC (20 % task), and also when 20 % MVC was preceded by either no contraction (0-20 task), by stronger muscle contraction (40-20 task) or by no contraction with a previous strong contraction (40-0-20 task). The results show that the IEMG level was within the prescribed limits when 20 and 40 % stationary tasks were executed with and without visual feedback. In 0-20, 40-20, and 40-0-20 tasks, 20 % IEMG level was precisely controlled in the presence of visual feedback, but without visual feedback the IEMG and force during 20 % IEMG maintenance were significantly higher in the 40-0-20 task than those in 0-20 and 40-20 tasks. That is, without visual feedback, there were significant variations in muscle activity due to different prehistory of contraction. In stationary tasks, MEP amplitudes in 40 % task were higher than in 20 % task. MEPs did not differ significantly during maintenance of the 20 % level in tasks with different prehistory of muscle contraction with and without visual feedback. Thus, in spite of variations in muscle background activity due to different prehistory of contraction MEPs did not vary significantly. This dissociation suggests that the voluntary maintenance of IEMG level is determined not only by cortical mechanisms, as reflected by corticospinal excitability, but also by lower levels of CNS, where afferent signals and influences from other brain structures and spinal cord are convergent.

[Motor asymmetry and learning new skills in animals].

The aim was to examine the relationship between the ability to learn new motor skills and preference to the right or left front paw when performing manipulation movements in rats. As a new skill used the Morris water maze, in which the animals are initially trained to detect platform hidden under water at the swim of the sector of the opposite platform, and then when sailing from sectors on the left or the right of the platform. Preference paw was determined by using the taking of animal food from a narrow horizontal tube and, accordingly, the rats were divided into left-handedness and right-handedness. We found that when changing the place of launch, that is the first voyage from the left or right of the sector, are right-handed, unlike left-handed, spent significantly more time to find the platform.

[Control of different electromyogram levels of M. abductor pollicis brevis by means of visual feedback in healthy subjects].

We studied voluntary control of integrated electromyogram (IEMG) in the range of 20 +/- 5% and 40 +/- 5% of the IEMG of m. abductor pollicis brevis during its maximum voluntary contraction with and without visual feedback. Healthy subjects performed IEMG control with visual feedback in 5 trials; IEMG control with visual feedback in 5 trials for 5 days, and the reproduction of memorized IEMG value without visual feedback after 5 trials of IEMG under the visual control. The accuracy of IEMG control was estimated by the following parameters: time of IEMG being out of the required 10% range (ERROR); IEMG variability (VARIABILITY), and the bias of IEMG mean level (BIAS) during 30-sec trials. The IEMG control in the range of 20 +/- 5% with visual feedback improved in all subjects over the course of 5 trials. Within 5-day training, ERROR and VARIABILITY reduced on the first day only; during the last 4 days there was no accuracy increase. ERROR increased more than twice when the 20% IEMG level was reproduced without vision. The IEMG control in the range of 40 +/- 5% improved neither during 5 trials, nor during 5 days of training with visual feedback. ERROR increased for about 1.5 times when the 40% IEMG level was reproduced without vision. It was concluded that the motor system, particularly the motor cortex, could control the given level of muscle activity using the visual feedback.

[Regulation of motor behaviour].

The review is devoted to analysis of the basic links of motor behavior control systems: sensorimotor cortex, cerebellum, a red nucleus and striatum. The organization and communications of these structures and their participation in learning and memory processes are described. The synaptic neurotransmitter and nonsynaptic neuromodulatory systems innervating these structures are also described. Hierarchical synaptic networks are formed by GABA and glutamatergic systems. The nonsynaptic dopaminergic system innervates both of these structures, but carries out a modulatory function. The mesocorticolimbic dopaminergic system induces an emotional and motivational state - processes of reinforcement, and participates in realization of purposeful behavior. The nigrostriatal dopaminergic system, through triggering an endocellular signal and the processes ofphosphorylation and dephosphorylation modulates activity ofGABA and glutamatergic receptors ofdorsal striatum spiny neurons and adapted thalamocortical networks.

[Kinematic characteristics of the voluntary cyclic trunk movements in patients at the early stage of Parkinson's disease].

Patients with the initial stage of Parkinson disease (PD) and matched controls performed repetitive bendings and turnings in standing position. Tasks included trunk movements in each of the anatomical planes: sagittal, frontal and axial. Electromagnetic system Flock of Birds was used for movement registration. Sensors were fixed at different segments of subject's body. Joint angles in the ankle, hip and torso as well as coordinates of the center of pressure served as output parameters. The amplitudes of joint angles were found to be lower in PD patients. Performance of the axial rotation revealed most pronounced differences. Thus, the amplitudes of joint angles of trunk movements in different anatomical planes reliably discriminate between PD patients and healthy subjects.

Asymmetry in dopamine levels in the nucleus accumbens and motor preference in rats.

Several studies on mice have demonstrated a correlation between the concentrations of dopamine and its metabolites in the nucleus accumbens and asymmetry in forelimb preference. Dopamine concentrations were greater in the nucleus accumbens ipsilateral in relation to the preferred paw. Limb preference was demonstrated in rats during performance of a response consisting of withdrawing food from a horizontal tube. Brain tissue dopamine concentrations were estimated by high-performance liquid chromatography with electrochemical detection. The results showed that in "left-handed" rats, the dopamine concentration in the left nucleus accumbens was significantly greater than that in "right-handed" rats. In right-handed rats, the dopamine concentration in the right nucleus accumbens was greater than that in the left. The results obtained here are significantly consistent with data obtained in mice and support the suggestion that the dopamine level in rats is greater in the nucleus accumbens ipsilateral to the preferred limb.

[Effect of apomorphine injection into the nucleus accumbens on the limb preference in manipulation movements in rats].

The concentration of dophamine and its derivates is known to correlate with the degree of handedness in manipulative movements in rodents. In this work we studied a possibility to changing handedness in rats by injection of a dopamine agonist into the nucleus accumbens. Retrieving food from a horizontal tube was used to determine the limb preference (10 food retrievals by the preferred limb). Then apomorphine was injected into the n. accumbens ipsilateral to the preferred limb in the course of 7 days. The same volume of buffer solution was injected into the contralateral n. accumbens. Just after the last injection the limb preference was tested. It was shown that the chronic injection of the non-specific agonist of dophamine receptors significantly changed the limb preference.

[Asymmetry in the dopamine content in the nucleus accumbens and the motor preference in rats].

A number of published studies reported a correlation between the paw preference in mice and asymmetry of tissue concentrations of dopamine (DA) and DA metabolites measured in the nucleus accumbens (NAcb) the DA concentration being higher in the nucleus ipsylateral to a preferred paw. This study aimed to investigate whether such asymmetry existed in rats. The paw preference was defined by reaching into a small horizontal tube for a food pellet. Tissue concentration of DA was measured by high-performance liquid chromatography with electrochemical detection. It was shown that the DA concentration in the left NAcb was significantly higher in "left-handed" rats than in "right-handed" animals. Within the group of "right-handers", the DA concentration was significantly higher in the right NAcb than in the left NAcb. The results confirm in part the experimental data obtained in mice and support the hypothesis that the paw preference is paralleled by elevated tissue DA in the ipsylateral NAcb of rodents.

Anticipatory postural adjustment before bimanual unloading reactions: the role of the motor cortex in motor learning.

The role of the motor cortex in forming a learned coordination (stabilization of the forearm on unloading) was studied in humans. Subjects maintained a 1-kg weight with the right (postural) forearm, the weight being attached via an electromagnet. Unloading of the postural arm was initiated by the subjects by lifting a similar load with the left arm. In control experiments, lifting of the load did not lead to unloading of the postural arm. Changes in motor cortex excitability were studied by transcranial magnetic stimulation applied to the representation area of the right biceps muscle in the motor cortex at the beginning and end of the experiments. Repeated unloading tests showed progressive decreases in the amplitude of the movement of the unloaded forearm, which were accompanied by increases in the anticipatory inhibition of the electromyogram of the biceps muscle of the unloaded arm (learning). Muscle responses to transcranial magnetic stimulation during the learning process showed no significant changes. Analysis of normalized muscle responses to transcranial magnetic stimulation (response/baseline) showed that these increased at the end of training and reached a significantly higher level than seen at the beginning of training. These results lead to the conclusion that the motor cortex plays a fundamental role in inhibiting synergies and coordinations which would interfere with the formation of the new coordination during motor learning.

Role of cerebellum in learning postural tasks.

For a long time, the cerebellum has been known to be a structure related to posture and equilibrium control. According to the anatomic structure of inputs and internal structure of the cerebellum, its role in learning was theoretically reasoned and experimentally proved. The hypothesis of an inverse internal model based on feedback-error learning mechanism combines feedforward control by the cerebellum and feedback control by the cerebral motor cortex. The cerebellar cortex is suggested to acquire internal models of the body and objects in the external world. During learning of a new tool the motor cortex receives feedback from the realized movement while the cerebellum produces only feedforward command. To realize a desired movement without feedback of the realized movement, the cerebellum needs to form an inverse model of the hand/arm system. This suggestion was supported by FMRi data. The role of cerebellum in learning new postural tasks mainly concerns reorganization of natural synergies. A learned postural pattern in dogs has been shown to be disturbed after lesions of the cerebral motor cortex or cerebellar nuclei. In humans, learning voluntary control of center of pressure position is greatly disturbed after cerebellar lesions. However, motor cortex and basal ganglia are also involved in the feedback learning postural tasks.

[Anticipatory postural adjustment in bimanual unloading: role of the motor cortex in motor learning].

The role of the motor cortex was investigated during learning unusual postural adjustment. Healthy subjects held their right (postural) forearm in a horizontal position while supporting a 1-kG load via an electromagnet. The postural forearm position was perturbed by the load release triggered by other elbow voluntary movement. Repetition of the imposed unloading test resulted in a progressive reduction of the maximal forearm rotation, accompanied by the anticipatory decrease in m. biceps brachii activity (learning). Control situation consisted of the voluntary forearm loading. Using the transcranial magnetic stimulation we examined changes in the motor evoked potential of the m. biceps brahii at the beginning and at the end of learning. The evoked potential amplitude did not significantly change in process of the decrease of m. biceps brachii activity. At the end of learning, motor evoked potential / baseline electromyogram ratio increased as compared to the beginning of learning and to the control situation. The results highlight the fundamental role of the motor cortex in suppression of synergies which interfere with formation of a new coordination during motor learning.

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.

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.

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.

[Recovery of motor skills after the caudate lesion in rats with the different prefered forelimb: the role of intense retraining].

Rats were trained for instrumental reaching (17 mm) of a sunflower seed from a horizontal tube 12 mm in diameter. After training, rats were divided into groups, "right-" and "left-handers", by the forelimb preference. Unilateral electrolytic lesions of the head of the caudate nucleus contralateral to the prefered forelimb were performed. After surgery, animals were retrained to perform the food-retrieval reaction by the same forelimb (reaching reaction by the "intact" forelimb was prohibited by a special bracelet). Both right- and left-handers were divided into groups of rare and intense retraining. Over the course of five months, animals of the groups of rare training were tested once a week, whereas the intense retraining was performed three or four times a week. Rats with right and left forelimb preference were shown to recover the reaching skill with different rates. In general, animals with left-side caudate lesion (right-handers) recovered the skill better both under condition of spontaneous recovery (rare testing) and intense retraining. The results suggest different mechanism of skill recovery after the right- and left-side brain lesion.

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.

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.

[Effects of prefrontal ablations on the reaction of the active choice of feeder under different probability and value of the reinforcement on dog]. / Vliianie kachestva i veroiatnosti podkrepleniia na vybor kormushek lobéktomirovannymi sobakami.

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.

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.

[Voluntary postural control learning with a use of visual bio-feedback in patients with spinocerebellar degenerations]. / Obuchenie proizvol'nomu kontroliu pozy s ispol'zovaniem zritel'noi obratnoi sviazi u bol'nykh spinotserebelliarnymi degeneratsiiami.

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.