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M E Ioffe

Publications and source records attributed to M E Ioffe.

At least 55 records · Page 3Linked to original sources
PubMedDate not supplied

[Participation of the motor cortex in the bimanual unloading task: a study by transcranial magnetic stimulation].

Motor potentials of m. biceps brachii evoked by transcranial magnetic stimulation of the contralateral motor cortex have been recorded in postural adjustment during arm unloading in humans. During active unloading, the amplitude of the motor evoked potential decreases simultaneously with the decreasing of the muscle activity. During load keeping, the muscle response changes simultaneously with the load changes. When the other arm has lifted the other load during load keeping, the amplitude of the motor evoked potential decreases in the m. biceps of the keeping arm without muscle activity changes. Passive unloading results in the same changes of the motor evoked potential as active unloading. A possible role of the direct corticospinal volley and the motor command mediated by some subcortical structures in the decrease of the muscle activity preceding active unloading (postural adjustment) is discussed.

Arm↗
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[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.

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[The mechanisms of motor learning].

In the paper the general principles of the motor learning are analyzed. A thesis is argued that instrumental conditioning is the basis of the motor learning, but the mechanisms of insight and the apparatus of anticipation of the action result also play an important role. At comparison of some theories of learning a hypothesis is suggested about the possibility of synthetic approach. Two stages can be distinguished in the process of the motor learning: formation of semantic and coordination programs. Formation and realization of learned movements opposite to the initial coordinations are constantly controlled by the motor cortex, which realizes the learned inhibition of the interfering coordinations.

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[Methods for the biomechanical description of different patterns of postural rearrangement in the motor learning of dogs].

The biomechanical description of spatial transfer of quadruped center of gravity is elaborated on the basis of analysis of vertical components of support pressures. The methods of evaluation of posture reconstruction pattern (coefficient of diagonally at all) are presented. The role of motor cortex in postural pattern reorganization in the process of learning in dogs is investigated by mean of this methods.

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[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.

Adult↗
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[The preference for one limb in rats--the result of learning in an experiment or an individual characteristic?].

The problem was studied whether an initial preference of one limb exists in rats connected with interhemispheric asymmetry or it appears during the procedure of testing (the first successful movement of one limb becomes consolidated). The work consisted in obtaining experimental retrograde amnesia after preliminary determination of the preferred limb and in the following testing of the preference after a definite time interval. In this case the trace of preceding learning must not influence the following choice of the limb. It is shown that the preference in rats is not a result of accidental learning in the experiment but initially exists before testing procedure. Retaining of memory trace for a long time (2-4 weeks) is also shown even after a very short learning (one-three successful movements).

Amnesia, Retrograde↗
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[Role of the motor area of the cortex in the performance of the postural escape reaction].

It has been shown on three dogs that unilateral ablation of the cortical motor area temporally disturbs previously acquired and opposite to the innate postural escape reaction to electric stimulation of the contralateral forepaw by increasing its pressure on the support. After 3-4 months of repeated training, compensation is possible. Bilateral ablation of the motor cortex elicits stable and unreversible disturbance of the acquired reaction. In reorganization of postural coordinations, motor cortex functions are connected with the inhibition of innate coordinations preventing performance of the reaction.

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[Motor asymmetry of the forelimbs of the rat].

Preference was studied of one of the forelimbs during performance of different manipulating movements in white rats. High degree of "handedness" was observed in all studied movements. However it was not absolute--no animals performed all movements by one and the same limb. Degree and character of "handedness" were different for different movements, though the number of "righthanded" rats in most tests as a whole exceeded the number of "lefthanded" ones. The "handedness" depends on the individuality of the animal, the character of the motor task, learning and interference of different motor tasks during training.

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[Effect of damage to the parietal associative cortex on the function of acquired motor coordination in dogs].

The effect of ablation of the parietal associative cortex on the performance of a complex food instrumental reaction was studied in dogs. The reaction consisted in two movements of the forelimb which were of similar pattern, but differed by their coordination. The first one was the lifting and holding of the paw at a required level for a required time, with the head in natural position (lifted), and the second one was the same movement of the paw with the head bent down for feeding, i.e. a new coordination, for the natural coordination consists in lowering of the forelimb associated with lowering of the head. During two sessions after the lesion, both reactions became irregular (so that the dogs performed only one of two movements or none). In the course of four months, the precision of the first movement was reduced, the amplitude of lifting the paw and duration of holding it were diminished. The new coordination persisted after ablation of the parietal associative cortex, though the holding (fixation) of the paw was less perfect. As was shown before by one of the present authors (M. E. Ioffe), lesion of the sensorimotor cortex resulted in profound disturbance of acquired coordination.

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[Disruption of elaborated motor coordination after destruction of the parietal and premotor association areas of the dog].

In experiments on seven dogs with a previously elaborated complex food-procuring reflex consisting of two instrumental movements, isolated damage of the parietal and premotor cortical areas deteriorated the achievement of exact movement--lifting and holding of the foreleg at the set level for a certain period of time. A second movement of lifting and holding the leg, similar to the first one, but with simultaneous lowering of the head during eating (altered inborn coordination) remained unaffected through the holding of the leg was also less stable. Successive damage of the parietal and premotor areas, worsening, but not significantly, the exact movement carried out in the natural posture, led to decomposition of the elaborated motor coordination revealed earlier (M. E. Ioffe, 1975) in case of the sensorimotor area damage. The role of the associative cortical areas in organization of elaborated coordination program is discussed.

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