Neuronal correlates of kinematics-to-dynamics transformation in the supplementary motor area

It is widely acknowledged that movements are planned at the level of the kinematics. However, the central nervous system must ultimately transform kinematic plans into dynamics-related commands. How, when, and where the kinematics-to-dynamics (KD) transformation is processed represent fundamental and unanswered questions. We recorded from the supplementary motor area (SMA) of two monkeys as they executed visually instructed reaching movements. We specifically analyzed a delay period following the instruction but prior to the go signal (motor planning). During the delay, a group of neurons in the SMA progressively came to reflect the dynamics rather than the desired kinematics of the upcoming movement. This finding suggests that some neurons in the SMA participate in the KD transformation.     

Creation of steady alterations of motor activity in chick embryos under conditions of controlled experiments]

Steady alterations of motor activity in chick embryos were demonstrated under conditions of a controlled experiment, in production regimens of various directions. During controlled support by electrocutaneous stimulation of threshold amplitudes of the movements, the following characteristic time periods were distinguished: transitional, of steady alterations of motor activity with minimization of the amount of electrostimuli, and of the period of aftereffect. The conclusion is drawn about the united adaptive effect (minimization of biologically adverse influences) provided by the biorhythm of motor activity with directional potentiation of the activity of the components, which are not supported by adverse effects.     

The control of mandible movements in the ant Odontomachus

Ants use their mandibles to manipulate many different objects including food, brood and nestmates. Different tasks require the modification of mandibular force and speed. Besides normal mandible movements the trap-jaw ant Odontomachus features a particularly fast mandible reflex during which both mandibles close synchronously within 3 ms. The mandibular muscles that govern mandible performance are controlled by four opener and eight closer motor neurons. During slow mandible movements different motor units can be activated successively, and fine tuning is assisted by co-activation of the antagonistic muscles. Fast and powerful movements are generated by the additional activation of two particular motor units which also contribute to the mandible strike. The trap-jaw reflex is triggered by a fast trigger muscle which is derived from the mandible closer. Intracellular recording reveals that trigger motor neurons can generate regular as well as particularly large postsynaptic potentials, which might be passively propagated over the short distance to the trigger muscle. The trigger motor neurons are dye-coupled and receive input from both sides of the body without delay, which ensures the synchronous release of both mandibles.     

Activity in the lateral prefrontal cortex reflects multiple steps of future events in action plans

To achieve a behavioral goal in a complex environment, we must plan multiple steps of motor behavior. On planning a series of actions, we anticipate future events that will occur as a result of each action and mentally organize the temporal sequence of events. To investigate the involvement of the lateral prefrontal cortex (PFC) in such multistep planning, we examined neuronal activity in the PFC of monkeys performing a maze task that required the planning of stepwise cursor movements to reach a goal. During the preparatory period, PFC neurons reflected each of all forthcoming cursor movements, rather than arm movements. In contrast, in the primary motor cortex, most neuronal activity reflected arm movements but little of cursor movements during the preparatory period, as well as during movement execution. Our data suggest that the PFC is involved primarily in planning multiple future events that occur as a consequence of behavioral actions.     

The central connections and actions during walking of tibial campaniform sensilla in the locust

Strain acting on the exoskeleton of insects is monitored by campaniform sensilla. On the tibia of a mesothoracic leg of the locust (Schistocerca gregaria) there are three groups of campaniform sensilla on the proximo-dorsal surface. This study analyses the responses of the afferents from one group, their connections with central neurones and their actions during walking.The afferents of the campaniform sensilla make direct excitatory connections with flexor tibiae motor neurones. They also make direct connections with particular spiking local interneurones that make direct inhibitory output connections with the slow extensor tibiae motor neurone.During walking extension movements of the tibiae during stance produce longitudinal tensile forces on the dorsal tibia that peak during mid stance before returning to zero prior to swing. This decline in tension can activate the campaniform sensilla. In turn this would lead to an inhibition of the extensor tibiae motor neurone and an excitation of the flexor tibiae motor neurones. This, therefore, aids the transition from stance to swing. During turning movements, the tibia is flexed and the dorsal surface is put under compression. This can also activate some of campaniform sensilla whose effect on the flexor motor neurones will reinforce the flexion of the tibia.     

Impedance characteristics of a neuromusculoskeletal model of the human arm II. Movement control

The modulation of neuromusculoskeletal impedance during movements is analysed using a motor control model of the human arm. The motor control system combines feedback and feedforward control and both control modes are determined in one optimization process. In the model, the stiffness varies at the double movement frequency for 2-Hz oscillatory elbow movements and has high values at the movement reversals. During goal-directed two-degrees-of-freedom arm movements, the stiffness is decreased during the movement and may be increased in the initial and final phases, depending on the movement velocity. The stiffness has a considerable curl during the movement, as was also observed in experimental data. The dynamic stiffness patterns of the model can be explained basically by the α−γ coactivation scheme where feedback gains covary with motor control signals. In addition to the modulation of the gain factors, it is argued that the variation of the intrinsic stiffness has a considerable effect on movement control, especially during fast movements. Received: 14 October 1997 / Accepted in revised form: 18 May 1999     

Interlimb interactions during cyclic in-phase and antiphase movements of arms and legs and their dependence on afferent influences

Coordinated arm and leg movements imply neural interactions between the rhythmic generators of the upper and lower extremities. In ten healthy subjects in the lying position, activity of the muscles of the upper and lower extremities was recorded during separate and joint cyclic movements of the arms and legs with different phase relationships between the movements of the limbs and under various conditions of the motor task. Antiphase active arm movements were characterized by higher muscle activity than during the inphase mode. The muscle activity during passive arm movements imposed by the experimentalist was significantly lower than muscle activity during passive arm movements imposed by the other arm. When loading one arm, the muscle activity in the other, passively moving, arm increased independently from the synergy of arm movements. During a motor task implementing joint antiphase movements of both upper and lower extremities, compared to a motor task implementing their joint in-phase movements, we observed a significant increase in activity in the biceps brahii muscle, the tibialis anterior muscle, and the biceps femoris muscle. Loading of arms in these motor tasks has been accompanied by increased activity in some leg muscles. An increase in the frequency of rhythmic movements resulted in a significant growth of the muscle activity of the arms and legs during their cooperative movements with a greater rate of rise in the flexor muscle activity of the arms and legs during joint antiphase movements. Thus, both the spatial organization of movements and the type of afferent influences are significant factors of interlimb interactions, which, in turn, determine the type of neural interconnections that are involved in movement regulation.     

Unitary activity in the cat motor cortex during a conditioned postural adjustment reflex

Unitary activity in the motor cortex (area 4) during a conditioned postural adjustment reflex was investigated in cats. Responses of the overwhelming majority of neurons connected with conditioned-reflex placing movements were activational in type. They consisted of several components and preceded the movements themselves by 50–600 msec. During realization of incorrect responses to presentation of a differential stimulus and of "spontaneous" interstimulus movements, the unitary responses were similar in direction but differed in their lower intensity and, in most cases, they appeared simultaneously with these movements. In the course of extinction both the conditioned-reflex movements and the corresponding unitary responses disappeared simultaneously. The technique of formation of a conditioned postural adjustment reflex suggested in this paper can be used to from natural, well-coordinated forelimb movements in animals in response to conditioned stimulation which are necessary initial components of more complex behavioral motor responses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 745–753, November–December, 1984.     

fMRI responses of the brain during active and passive movements in left-handed subjects

The hemodynamic (magnetic resonance imaging, fMRI, 3T) brain responses were studied in 15 left-handed healthy subjects performing active and passive movements of the dominant and non-dominant hands. Group and individual fMRI responses to the motor load were analyzed. It was found that, during the active movements of dominant and non-dominant hands, the main activation cluster appeared in the preand postcentral gyrus of the contralateral hemisphere and which topographically similar during active and passive movements. The activation cluster of greater volume was identified in these areas; the response was more diffused during the non-dominant hand movements in comparison with the dominant hand. During passive movements, the cortical activation clusters of a smaller volume in comparison with the active movements were found, which was expressed most clearly during the performance of non-dominant hand movements and could reflect the weakening of the control from the cortical structures in these conditions.     

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.     

Catecholaminergic and cholinergic regulation of swimming motility development in free embryos of Cichlasoma Nigrofasciatum

The divergence of progeny from the same spawners of Cichlasoma nigrofasciatum into two groups by duration of embryogenesis and the level of motor activity was studied close to the end of the embryonic period. Free embryos were also studied. During the study, eggs were treated with agents, modifying the activity of catecholaminergic and cholinergic systems. 3-Hydroxytyramine and L-Tyrosine were found to exert a weak influence on embryonic motility. After hatching, these substances modify swimming performance of free embryos, approximating movements of fish at later stages. 6-Hydroxydopamine and, still more, alpha-Bungarotoxin, decrease embryonic motility and postpone the hatching. The influence of these substances on the development of embryo motility increases during early ontogenesis, as indicated by decreased concentration of the substance, necessary for adequate reaction. Neither L-Tyrosine nor 6-Hydroxydopamine influenced the divergence of the progeny into two groups. Injection of the perivitelline fluid with high concentration of hatching enzyme from pre-hatching embryos into the perivitelline space of earlier embryos was found to induce the appearance of rotation movements, typical for more advanced embryos. Changes of correlation between the miogenic and neurogenic motor activity during early development of fish are discussed.     

A kinematic analysis of the formation of precise instrumental movements in cats

Kinematic parameters of cats local manipulating movements have been studied in the process of formation and stabilization of precise habit of moving and holding the lever in the zone of "working" space signalled by sound. It is shown that change of activity of the motor control system in the course of training is connected with the transfer from current correction of performed reaction to optimization of controlled parameters of pre-paired movements. It has been established that the formed precise coordination is realized owing to rapid movements with monomodal asymmetric profile of speed. During habit stabilization time to peak velocity significantly dropped from 274.6 +/- 84.7 to 211.0 +/- 22.9 ms and its value increased from 119.5 +/- 27.8 to 182.2 +/- 44.4 degrees/s. The stabilized habit is provided by uniform movements of ballistic type and characterized by independence from sound indication of final position, its reaching time becoming a function of amplitude-temporal values of speed maximum. It has been found that in the process of motor learning the relation of the duration of acceleration growth to the beginning of movement inhibition becomes an invariant parameter of the central program of precise reactions.     

Control of climbing behavior in the cockroach, Blaberus discoidalis. II. Motor activities associated with joint movement

Deathhead cockroaches employ characteristic postural strategies for surmounting barriers. These include rotation of middle legs to re-direct leg extension and drive the animal upward. However, during climbing the excursions of the joints that play major roles in leg extension are not significantly altered from those seen during running movements. To determine if the motor activity associated with these actions is also unchanged, we examined the electromyogram activity produced by the slow trochanteral extensor and slow tibial extensor motor neurons as deathhead cockroaches climbed over obstacles of two different heights. As they climbed, activity in the slow trochanteral extensor produced a lower extension velocity of the coxal-trochanteral joint than the same frequency of slow trochanteral extensor activity produces during horizontal running. Moreover, the pattern of activity within specific leg cycles was altered. During running, the slow trochanteral extensor generates a high-frequency burst prior to foot set-down. This activity declines through the remainder of the stance phase. During climbing, motor neuron frequency no longer decreased after foot set-down, suggesting that reflex adjustments were made. This conclusion was further supported by the observation that front leg amputees generated even stronger slow trochanteral extensor activity in the middle leg during climbing movements.     

Specificity of nuclear elements of the motor region of the cortex in organizing a precise motor response

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.     

Les mouvements révolutifs des feuilles deMimosa pudica L

The nutational movements performed by the leaves of the “Sensitive plant”,Mimosa pudica L., result from periodical turgor variations taking place in the parenchymatous cells of specialized motor organs. The trajectories in the three kinds of leaf motor organs usually show irregular elliptical paths with a period ranging from 10 to 60 min. The morphological analogy of these turgor movements is discussed in relation to nutational movements observed in growing organs.      

Modular organization of finger movements by the human central nervous system

The motor system may generate automated movements, such as walking, by combining modular spinal motor synergies. However, it remains unknown whether a modular neuronal architecture is sufficient to generate the unique flexibility of human finger movements, which rely on cortical structures. Here we show that finger movements evoked by transcranial magnetic stimulation (TMS) of the primary motor cortex reproduced distinctive features of the spatial representation of voluntary movements as identified in previous neuroimaging studies, consistent with naturalistic activation of neuronal elements. Principal component analysis revealed that the dimensionality of TMS-evoked movements was low. Principal components extracted from TMS-induced finger movements resembled those derived from end-postures of voluntary movements performed to grasp imagined objects, and a small subset of them was sufficient to reconstruct these movements with remarkable fidelity. The motor system may coordinate even the most dexterous movements by using a modular architecture involving cortical components.     

Functional organization of the cortex of the large hemispheres during voluntary movement performance: Age aspect

The method of estimation of the coherence (Coh) function values of EEG rhythmic components disclosed the specific features of functional associations of cortical regions during the performance of voluntary graphic cyclic movements under usual and unusual conditions. A significant increase in the Coh function values of the α-rhythm was observed both in the contralateral hemisphere and the symmetrical central and parietal cortical regions in adult subjects during right-hand movement performance with open eyes (usual conditions); in this case the resulting functional associations included motor zone and cortical regions responsible for visual information analysis and perception. During right- and left-hand movement performance with closed eyes (unusual conditions), the mature-type functional organization had a bilateral character with interrelated activity focused in the frontal regions that clearly demonstrated the function of these structures during formation of new motor programs. The significant changes in cortical mechanisms of voluntary graphic movements were disclosed in young 7- to 8- and 9- to 10-year-old schoolchildren.     

Fast ballistic food-procuring movements in rats: Phenomenology and probable controlling mechanisms

Parameters of fast ballistic food-procuring movements were studied in albino rats. With the use of video and photorecording, the number of attempts used by an animal, to get the food globula, duration of the movements, and their phasic structure were analyzed within the whole learning period and certain experimental days. When the motor skill had been formed, programed ballistic components characterized by hard-to-modify parameters and components with a considerable impact of reverse afferentation in their formation and performance were analyzed. The experimental data are interpreted in terms of the expediency of using the operant motor reactions performed by rats getting food from a narrow manger as a model of voluntary motor activity in electrophysiological, behavioral, neurochemical, and morphological studies. The regularities in formation of motor programs, initiation, realization, and control of the movements, and central mechanisms of these phenomena are discussed.     

Effects of vanadate, N2 and light on the membrane potential of motor cells and the lateral leaflet movements of Desmodium motorium

The lateral leaflets of Desmodium motorium (Houtt.) Merr. exhibit ultradian up- and down movements, which are paralleled by oscillations of the membrane potential of motor cells in the pulvinus. By different treatments we have tested the hypothesis that both that both oscillation-types are causally related. The reactions of the leaflet movement and the membrane potential were evaluated by the following approaches. (1) Application of vanadate. an inhibitor of the proton pump in the plasmalemma. and N₂ suppressed leaflet movements and finally arrested the leaflet in the lower position. Before the oscillations damped out, a strong lengthening in period was found. This indicates that the pump is part of the ultradian clock. A period lenthening and a final suppression of the rhythm by vanadate was also seen in the extracellular electric potential of the pulvinus. Intracellular recordings in situ showed that vanadate application depolarized the motor cells. (2) Light of high fluence rates diminished the amplitude of the oscillations of the membrane potential of single motor cells and shortened the period. The same effects were observed when monitoring the lateral leaflet movement. The leaflet always moved towards the direction of the light. whether it was applied from the abaxial or from the adaxial part of the pulvinus. (3) When light was applied to the pulvinus of lateral leaflets. which had spontancously stopped moving in an upper position. oscillations were induced transiently. This effect was also found for the membrane potential of motor cells in the pulvinus. - Our results thus provide further evidence that the membrane potential controls the volume state of the motor cells in the pulvinus of lateral leaflets of Desmodium motorium .