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PubMed1992

The effects of objectives and constraints on motor control strategy in reciprocal aiming movements.

The goal of this study was to examine how the kinematics of reciprocal aiming movements were affected by both the objective of the movement and the constraints operating on that movement. In Experiment 1, the objective of the movement was indirectly manipulated by capitalizing on the fact that subjects determine their own accuracy and speed limits, despite uniform task instructions to move as quickly and accurately as possible. A Fitts' type reciprocal aiming paradigm was employed, in which 69 subjects were asked to move a stylus repetitively between two spatially separated targets. Four target widths were orthogonally combined with four movement amplitudes, resulting in 16 conditions. Movements were made on an X-Y digitizing tablet. Based on the mean variable error produced on both targets, subjects were differentiated post hoc into three movement objective groups: speed, accuracy, and speed-plus-accuracy. Kinematic analyses revealed that the programming and execution of movements were systematically influenced by both the movement objective and the movement constraints. That is, movement time, peak velocity, dwell time, acceleration and deceleration time, normalized acceleration and normalized deceleration varied systematically as a function of both the speed-accuracy movement objective and the movement constraints of target size and movement distance. Moreover, the consequences of changing the constraints of the movement were affected by an interaction with the objective of the movement. In Experiment 2, the objective of the movement was directly manipulated by varying speed and/or accuracy instructions to subjects. The basic results of Experiment 1 were substantiated. Overall, the results were consistent with the view that motor control is dependent upon sensory consequences.

Journal Article↗
PubMed2006

Comparison of visual and objective quantification of elbow and shoulder movement in children with obstetric brachial plexus palsy.

BACKGROUND: The Active Movement Scale is a frequently used outcome measure for children with obstetric brachial plexus palsy (OBPP). Clinicians observe upper limb movements while the child is playing and quantify them on an 8 point scale. This scale has acceptable reliability however it is not known whether it accurately depicts the movements observed. In this study, therapist-rated Active Movement Scale grades were compared with objectively-quantified range of elbow flexion and extension and shoulder abduction and flexion in children with OBPP. These movements were chosen as they primarily assess the C5, C6 and C7 nerve roots, the most frequently involved in OBPP. Objective quantification of elbow and shoulder movements was undertaken by two-dimensional motion analysis, using the v-scope. METHODS: Young children diagnosed with OBPP were recruited from the Royal Children's Hospital (Melbourne, Australia) Brachial Plexus registry. They participated in one measurement session where an experienced paediatric physiotherapist facilitated maximal elbow flexion and extension, shoulder abduction and extension through play, and quantified them on the Active Movement Scale. Two-dimensional motion analysis captured the same movements in degrees, which were then converted into Active Movement Score grades using normative reference data. The agreement between the objectively-quantified and therapist-rated grades was determined using percentage agreement and Kappa statistics. RESULTS: Thirty children with OBPP participated in the study. All were able to perform elbow and shoulder movements against gravity. Active Movement Score grades ranged from 5 to 7. Two-dimensional motion analysis revealed that full range of movement at the elbow and shoulder was rarely achieved. There was moderate percentage agreement between the objectively-quantified and therapist-rated methods of movement assessment however the therapist frequently over-estimated the range of movement, particularly at the elbow. When adjusted for chance, agreement was equal to chance. CONCLUSION: Visual estimates of elbow and shoulder movement in children with OBPP may not provide true estimates of motion. Future work is required to develop accurate, clinically-acceptable methods of quantifying upper limb active movements. Since few children attained full range of motion, elbow and shoulder movement should be monitored and maintained over time to reduce disability later in life.

Journal Article↗
PubMed2004

Predictive strategies in interception tasks: differences between eye and hand movements.

To investigate how the sensorimotor systems of eye and hand use position, velocity, and timing information of moving targets, we conducted a series of three experiments. Subjects performed combined eye-hand catch-up movements toward visual targets that moved with step-ramp-like velocity profiles. Visual feedback of the hand was prevented by blanking the target at the onset of the hand movement. A multiple regression was used to determine the effects of position, velocity, and timing accessed before each movement on the movement amplitudes of eye and hand. The following results were obtained: 1. The predictive strategy of eye movements could be modeled by a linear regression on the basis of the position error and the target velocity. This was not the case for hand movements, for which there was a significant partial correlation between the movement amplitude and the product of target velocity and movement duration. This correlation was not observed for eye movements suggesting that the predictive strategy of hand movements takes movement duration into account, in contrast to the strategy used in eye movements. 2. To determine whether the movement amplitudes of eye and hand depend on a categorical classification between a discrete number of movement types, we compared an experiment in which target position and velocity were distributed continuously with an experiment using only four different combinations of target position and velocity. No systematic differences between these experiments were observed. This shows that the system output is a function of continuous, interval-scaled variables rather than a function of discrete categorical variables. 3. We also analyzed the component of the movement amplitudes not explained by the regression, i.e., the residual error. The residual errors between subsequent trials were correlated more strongly for eye than for hand movements, suggesting that short-term temporal fluctuations of the predictive strategy were stronger for the eye than for the hand.

Adult↗
PubMed2006

Adapting movement planning to motor impairments: the motor-scanning system.

Previous studies have reported a similar duration for movement execution (real movement) and its internal simulation with motor imagery (virtual movement). The present work has studied the real movement-virtual movement relationship for complex sequences of finger movements after different acute and chronic brain lesions and after a long-lasting restriction of right-hand movements. Age, hand-movement restriction and lesions of pyramidal system, basal ganglia and cerebellum did not prevent the high real movement-virtual movement correlation. The data suggest that movement execution and its internal simulation share the same neuronal basis. However, the calculation of virtual delay (a useful procedure for detecting small real movement-virtual movement differences) showed significant real movement-virtual movement mismatches, suggesting the existence of a separate and selective system that, continuously scanning the competence of the different elements participating in motor behavior, adjusts the planning of future movements to the real capability of the motor system.

Adult↗
PubMed1990

Single unit analysis of the human ventral thalamic nuclear group. Activity correlated with movement.

During neurosurgical operations for the relief of movement disorders, single thalamic neurons (n = 107) were identified with activity which was related to verbally cued active movements (movement-related cells). The activity of each neuron was examined during different contralateral movements in order to determine the movement which was associated with the most consistent and pronounced change in firing rate (the optimal response). The optimal response was determined by analysis of histograms of neuronal activity which were constructed by using the onset of EMG activity to synchronize successive repetitions of the active movement. Movement-related cells exhibited optimal responses associated with such movements as making a fist, extension or flexion of the wrist, flexing or extending the elbow, pointing with the entire upper extremity, extending the tongue and lifting the leg. Most movement-related cells recorded in a single parasagittal plane in an individual patient had optimal responses related to movements involving the same part of the body. Movement-related cells were classified into those that were activated in response to somatosensory stimulation (combined cells, n = 20) and those which were not (voluntary cells, n = 87). Combined cells were activated in advance of EMG activity during active movement and so could be distinguished from cells responding only to sensory stimulation (sensory cells). Movement-related cells (combined and voluntary cell types) were located anterior to sensory cells and tended to show a mediolateral somatotopic organization parallel to that of sensory cells with cutaneous receptive fields. Combined cells responded to somatosensory stimulation of the same part of the body as that involved in the active movement related to the optimal response of the cell. Combined cells responding to passive movements of a joint always had their optimal response during active movement about the same joint. The activity of combined cells during parkinsonian tremor may clarify the role of sensory feedback in tremor.

Electric Stimulation↗
PubMed1989

Deficits in reaction times and movement times as correlates of hypokinesia in monkeys with MPTP-induced striatal dopamine depletion.

1. We quantitatively assessed deficits in the initiation and execution of arm movements occurring after destruction of nigrostriatal dopamine neurons by systemic administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) (Sigma). Three monkeys performed a reaction time task in which they reached toward a single and constant target for food reward. 2. After administration of MPTP, all three monkeys showed hypokinesia necessitating dopamine precursor or receptor agonist treatment. The partial recovery of one animal from initial akinesia after 19 days permitted discontinuation of dopaminergic drug therapy, although marked hypokinesia remained present. The two other animals displayed additional, intermittent phases of rigidity and activation tremor and needed continuous dopaminergic drug therapy for most of the postlesion period. 3. Administration of MPTP significantly prolonged EMG reaction time in prime mover muscles and arm movement reaction time by 47-225% and 18-129%, respectively, on the six sides of the three animals, compared with control measurements before the lesion. EMG and arm movement reaction time increased over consecutive trials in most sessions comprising 110-130 movements, the first 20 movements showing almost normal values. The delay time between onsets of EMG and arm movement showed unsystematic changes. These deficits in movement initiation were observed both with and without dopamine precursor therapy. They lasted during the whole testing period of several months. 4. Linear correlations between arm movement onset and EMG onset in the two prime mover muscles, the extensor digitorum communis and the biceps, showed coefficients of mostly 0.7-0.9, both before and after MPTP. These data suggest that the temporal relationship between onsets of arm movement and EMG were not substantially affected by MPTP. 5. Arm movement time was divided into two phases. The duration of movement between the resting key and the target, a small food-containing box located ahead of the animal, was denoted as reaching movement time. The following hand manipulation inside the food box was measured as box movement time. After MPTP, both measures were significantly prolonged by 10-103% and 12-251%, respectively, on the six sides of the three monkeys. These deficits in movement execution were observed both with and without dopaminergic drug therapy and during the whole testing period. 6. Task performance after MPTP treatment was studied in one monkey in the absence of dopaminergic drug therapy. EMG and arm movement reaction times recovered partially over several weeks, while the prolongations in reaching and box movement times remained unchanged.(ABSTRACT TRUNCATED AT 400 WORDS)

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1991

Multiple representations of body movements in mesial area 6 and the adjacent cingulate cortex: an intracortical microstimulation study in the macaque monkey.

The mesial agranular frontal cortex that lies rostral to area 4 (F1) is formed by two distinct cytoarchitectonic areas: F3, located caudally, and F6, located rostrally. In the present experiments we investigated the organization of F3 and F6 by observing the motor responses evoked by their intracortical electrical microstimulation. Our main purpose was to find out whether the cytoarchitectonic subdivision of the mesial agranular frontal cortex into two areas has a physiological counterpart. The result showed that F3 (the caudal area) contains a complete motor representation with hindlimb movements located caudally, forelimb movements located centrally, and orofacial movements located rostrally. The great majority of limb movements involved proximal joints. With respect to F1, F3 showed the following functional characteristics: (1) lack of segregation between proximal and distal movements, (2) larger percentage of complex movements, and (3) higher excitability threshold. Movements were more difficult to elicit from F6 (the rostral area) than from F3. However, by using a longer stimulus train duration (100 ms) 39.3% of tested sites produced body movements. This percentage increased (50.5%) when the electrical stimulation was applied during monkey natural movements instead of when the monkey was still in its chair. Most of the evoked movements concerned the forelimb. More rarely, neck and upper face movements were observed. Unlike F1 and F3 where most movements were fast, slow movements were frequently observed with stimulation of F6. Many of them mimicked natural movements of the animal. Eye movements were evoked from F7 (superior area 6) but not from F6. An additional motor representation was found in the dorsocaudal part of area 24 (24d). This area is topographically organized with a forelimb representation located caudally and ventrally and a hindlimb representation located rostrally and dorsally. The excitability threshold of area 24d is higher than that of F1 and F3. Evoked movements were occasionally observed also after stimulation of area 24c. In conclusion, on the mesial cortical wall rostral to F1, there are at least three independent motor representations. On the basis of somatotopic organization and excitability properties, we propose that the term supplementary motor area (SMA-proper) should be reserved to F3.

Animals↗
PubMed1992

Basic functions of variability of simple pre-planned movements.

A model of a pre-planned single joint movements performed without feedback is considered. Modifications of this movement result from transformation of a trajectory pattern f(t) in space and time. The control system adjusts the movement to concrete external conditions specifying values of the transform parameters before the movement performance. The pre-planned movement is considered to be simple one, if the transform can be approximated by an affine transform of the movement space and time. In this case, the trajectory of the movement is x(t) = Af (t/tau + s) + p, were A and l/tau are space and time scales, s and p are translations. The variability of movements is described by time profiles of variances and covariances of the trajectory x(t), velocity v(t), and acceleration a(t). It is assumed that the variability is defined only by parameters variations. From this assumption follows the main finding of this work: the variability time profiles can be expanded on a special system of basic functions corresponding to established movement parameters. Particularly, basic functions of variance time profiles, reflecting spatial and temporal scaling, are x2(t) and t2v2(t) for trajectory, v2(t) and (v(t)+t.a(t))2 for velocity, and a2(t) and (2a(t)+t.j(t))2, where j(t) = d3x(t)/dt3, for acceleration. The variability of a model of a reaching movement was studied analytically. The model predicts certain peculiarities of the form of time profiles (e.g., the variance time profile of velocity is bi-modal, the one of acceleration is tri-modal, etc.). Experimental measurements confirmed predictions. Their consistence allows them to be considered invariant properties of reaching movement. A conclusion can be made, that reaching movement belongs to the type of simple pre-planned movements. For a more complex movement, time profiles of variability are also measured and explained by the model of movements of this type. Thus, a movement can be attributed to the type of simple pre-planned ones by testing its variability.

Elbow Joint↗
PubMed1996

Control of remembered reaching sequences in monkey. I. Activity during movement in motor and premotor cortex.

Motor and premotor cortex firing patterns from 307 single neurons were recorded while monkeys made rapid sequences of three reaching movements to remembered target buttons arrayed in two-dimensional space. A primary goal was to study and compare directionally tuned responses for each of three movement periods during 12 movement sequences that uniformly sampled the directional space in front of the monkey. The majority of neurons showed maximal responses during movements in a preferred direction with smaller increases during movements close to the preferred direction. These responses showed a statistically significant regression fit to a cosine function for 72% of the neurons examined. Comparisons among tuning directions computed separately for the first, second, and third movement periods suggested the near constancy of preferred direction across a rapidly executed series of movements even though these movements began at different starting points in space. Although directionally tuned neurons were only broadly tuned for a specific direction of movement, the neuronal ensemble carried accurate directional information. A population vector computed by summing vector contributions from the entire population of tuned neurons predicted movement direction with a mean accuracy of 20 degrees. This population code made consistent predictions for each of the 36 movements that were studied using a single set of population parameters. Most of the remaining neurons (24%) that were not tuned during movement did show significant changes in activity during other aspects of task performance. Some nontuned neurons had nondirectional increases that were sustained during movement, while others showed identical phasic bursts during the three movement periods. These nontuned neurons may control stabilizations of the shoulder, trunk, and forearm during movement, or forearm movements during button pushing.

Animals↗
PubMed1989

A kinematic comparison of single and multijoint pointing movements.

Rapid pointing movements (no accuracy or reaction time requirements) were performed under three conditions which limited motion to the shoulder, elbow or a combination of these two joints. Velocity profiles of the hand's trajectory differed during single and multijoint movements. For the same magnitude of displacement, the hand always had a higher peak velocity, shorter rise time (time to peak velocity) and shorter movement time during single joint movements. However, when the profiles were normalized with respect to amplitude and movement time, no significant differences were observed between these three movement conditions. The velocity profiles of the elbow and/or shoulder were also compared under single and multijoint movement conditions. Analysis of these profiles revealed that the relationships between peak velocity and displacement and between movement time and displacement remained the same at the shoulder joint during single and multijoint movements. In contrast, the elbow joint velocity profiles were significantly affected by movement conditions. These relationships (peak velocity/displacement and movement time/displacement) changed during multijoint movements and became the same as those observed at the shoulder joint. The shape of the hand velocity profile and its invariance across movement conditions can best be explained by dynamic optimization theory and supports the notion that movement of the hand is of primary importance during rapid pointing. However, the consistency of the shoulder velocity profile and the highly significant relationships between the movement of the elbow and shoulder joints indicates that a subordinate joint planning strategy is also used. The purpose of this strategy is to functionally decrease the available degrees of freedom and to simplify coordination between the moving joints. Thus, the organization of arm movements is hierarchically structured with important, but different contributions being made on both the hand planning and joint planning levels.

Adult↗
PubMed1991

Modulation of the cutaneous responsiveness of neurones in the primary somatosensory cortex during conditioned arm movements in the monkey.

The present experiments were designed to investigate the neuronal mechanisms, at the level of the primary somatosensory cortex, which underlie the observation that somatosensory cortical potentials evoked by air puff stimuli directed at the forearm are decreased, in a nonspecific and widespread manner, during voluntary movements about the elbow. Unitary discharge was recorded from 131 cells receiving cutaneous input from the hairy skin of the forearm or hand (areas 3b and 1) of two monkeys trained to perform rapid movements of the contralateral arm (elbow flexion or extension). Evoked unitary responses to air puff stimuli applied to the centre of the cell's receptive field, at various delays before and after the onset of movement, were recorded. Movement produced a significant decrease in the short latency excitatory response to the air puff in 89% of the cells (117/131); the remaining 11% were not modulated by movement. This movement-related "gating" of cutaneous inputs occurred regardless of the response pattern of the cells to movement alone, being observed in 91% of the cells with no movement-related discharge, and 89% of those with movement-related discharge. The air puff responses of cells with inputs from the forearm and the dorsum of the hand were all similarly modulated by movement and the modulation was clearly present prior to the onset of movement (mean onset, -66 ms). Variation in the depth of modulation as a function of the direction of the movement, flexion or extension, was observed in only a very small proportion of the modulated units (16/117); most showed no relationship to direction. It is suggested that, in this experimental situation, much of the modulation appears to occur at a pre-cortical level since there was no relationship between the pattern of discharge of cells in relation to movement alone and the pattern of movement-related gating of their responses to the air puff. Effects which might be consistent with a cortical origin for the modulation were only infrequently observed. The present results are strikingly similar to those obtained using the evoked potential method, and thus support the hypothesis that in this task of rapid elbow movements, movement modulates the transmission of cutaneous signals from the hairy skin of the distal forelimb to primary somatosensory cortex in a nonspecific and widespread fashion.

Animals↗
PubMed1987

Voluntary smooth eye movements with foveally stabilized targets.

We investigated the capacity of 6 humans to make voluntary smooth eye movements with a horizontally stabilized foveal point target. When the target was viewed on a dark field, all subjects were able to make smooth oscillatory eye movements when they attempted to imitate their own normal pursuit of sinusoidal target movement (0.2-0.7 Hz) directly preceding the stabilization on the fovea. The frequency of the imitating eye movement was in general lower than the frequency of normal pursuit by 2-35%. While fixating a foveally stabilized point target superimposed on a large, sinusoidally moving non-stabilized background, all subjects were able to make either no eye movements, eye movements nearly in phase with or eye movements nearly in counterphase with the background movement depending on the instruction to imagine the target as head-stationary, moving in phase, or moving in counterphase with the background. The accuracy of the frequency of the smooth eye movement with the stabilized target on the moving background was higher than during imitation of pursuit on the dark field but the precision of the frequency was lower than during normal pursuit. When the background moved pseudo-randomly all subjects could voluntarily inhibit their smooth eye movements or could make smooth eye movements in phase with the background. Only 2 subjects showed a limited ability to make smooth eye movements opposite to the pseudo-random background movement. The results suggest that with predictable background movement the volition of the subject rather than the movement of the background determines the eye movements when the subject looks at the foveally stabilized target.

Eye Movements↗
PubMed1999

Pointing in 3D space to remembered targets. II. Effects of movement speed toward kinesthetically defined targets.

The accuracy of visually guided pointing movements decreases with speed. We have shown that for movements to a visually defined remembered target, the variability of the final arm endpoint position does not depend on movement speed. We put forward a hypothesis that this observation can be explained by suggesting that movements directed at remembered targets are produced without ongoing corrections. In the present study, this hypothesis was tested for pointing movements in 3D space to kinesthetically defined remembered targets. Passive versus active acquisition of kinesthetic information was contrasted. Pointing errors, movement kinematics, and joint-angle coordination were analyzed. The movements were performed at a slow speed (average peak tangential velocity of about 1.2 m/s) and at a fast speed (2.7 m/s). No visual feedback was allowed during the target presentation or the movement. Variability in the final position of the arm endpoint did not increase with speed in either the active or the passive condition. Variability in the final values of the arm-orientation angles determining the position of the forearm and of the upper arm in space was also speed invariant. This invariance occurred despite the fact that angular velocities increased by a factor of two for all the angles involved. The speed-invariant variability supports the hypothesis that there is an absence of ongoing corrections for movements to remembered targets: in the case of a slower movement, where there is more time for movement correction, the final arm endpoint variability did not decrease. In contrast to variability in the final endpoint position, the variability in the peak tangential acceleration increased significantly with movement speed. This may imply that the nervous system adopts one of two strategies: either the final endpoint position is not encoded in terms of muscle torques or there is a special on-line mechanism that adjusts movement deceleration according to the muscle-torque variability at the initial stage of the movement. The final endpoint position was on average farther from the shoulder than the target. Constant radial-distance errors were speed dependent in both the active and the passive conditions. In the fast speed conditions, the radial distance overshoots of the targets increased. This increase in radial-distance overshoot with movement speed can be explained by the hypothesis that the final arm position is not predetermined in these experimental conditions, but is defined during the movement by a feedforward or feedback mechanism with an internal delay.

Acceleration↗
PubMed2001

Combined visual attention and finger movement effects on human brain representations.

Sensory and motor systems interact in complex ways; visual attention modifies behavior, neural encoding, and brain activation; and dividing attention with simultaneous tasks may impede performance while producing specific brain activation patterns. We hypothesized that combining voluntary movement with visual attention would yield unique brain representations differing from those occurring for movement or visual attention alone. Hemodynamic signals in humans were obtained with functional magnetic resonance imaging (MRI) while participants performed one of four tasks that required only a repetitive finger movement, only attending to the color of a visual stimulus, simultaneous finger movement and visual attention, or no movement and no visual attention. The movement-alone task yielded brain activation in structures commonly engaged during voluntary movement, including the primary motor cortex, supplementary motor area, and cerebellum. Visual attention alone resulted in sparse cerebral cortical and substantial bilateral cerebellar activation. Simultaneous performance of visual attention and finger movements yielded widespread cerebral cortical, cerebellar, and other subcortical activation, in many of the same sites activated for the movement or attention tasks. However, the movement-related plus attention-related activation extended beyond the movement-alone or attention-alone activation sites, indicating a novel activation pattern related to the combined performance of attention and movement. Additionally, the conjoint effects of visual attention and movement upon brain activation were probably not simple gain effects, since we found activation-related interactions in the left superior parietal lobule, the right fusiform gyrus, and left insula, indicating a potent combinatory role for visual attention and movement for activation patterns in the human brain. In conclusion, performing visual attention and movement tasks simultaneously, even though the tasks had no specific interrelationship, resulted in novel activation patterns not predicted by performing movements or visual attention alone.

Adult↗
PubMed1976

Size and distribution of movement fields in the monkey superior colliculus.

A gradient of response magnitude was observed across the movement fields (the range of eye movements which alter the discharge frequency of a nueron) of neurons in the intermediate and deeper layers of the superior colliculus. A vigorous discharge preceded movements with a particular direction and amplitude but reduced responses preceded movements which deviated from this direction and/or amplitude. Movement field size is a function of the amplitude of the optimal movement. Neurons discharging prior to small saccades have small and sharply tuned fields. Neurons discharging prior to large saccades have large movement fields and tuning is relatively coarse. Movement fields are topographically organized within the superior colliculus. Neurons discharging prior to small saccades are located anteriorly; neurons firing before large saccades are found caudally. Neurons near the midline discharge prior to up movements and neurons located laterally fire before downward movements. Movement fields of superior colliculus neurons are also characterized by a temporal gradient. The interval between spike discharge and the onset of a saccade is greater for movements near the center of the movement field than for movements to the periphery of the field. Results are interpreted as supporting the foveation hypothesis of superior colliculus function. It is suggested that precise saccadic movements are not produced by the discharge of a small population of finely tuned neurons but result from the weighted sum of the simultaneous movement tendencies produced by the activity of a large population of less finely tuned neurons.

Animals↗
PubMed1987

Neuronal activity in nuclei pontis and reticularis tegmenti pontis related to forelimb movements of the monkey.

The activity of the pontine nucleus (PN) neuron was recorded in 3 monkeys moving a handle alternately from start to target zones in a simple extension-flexion movement at the wrist. Of 73 PN neurons related to the task, 44 were related to movement, 19 to handle holding and 5 to both movement and holding of the handle. Of the 44 movement-related neurons, 16 were related to flexion, 22 to extension, and 6 to both. In 37 of 54 analyzed movements of the PN neurons which were related to movements, or to both movements and handle holding, the change of the activity occurred before the movement. However, in most of these cases (24/37), discharge occurred less than 100 ms earlier than the start of the movement. In the remaining one-third of movements (17/54), neurons discharged after the onset of the movement. Locations of the 73 neurons were histologically verified in the pontine nucleus. Somewhat similar observations were made of 14 cells located in the nucleus reticularis tegmenti pontis (NRTP). Considering that the majority of movement-related PN and NRTP neurons discharged immediately before or even after the onset of movement, these neurons may play a role in the execution of movement, at least of a simple movement, rather than in the initiation or planning of movement.

Animals↗
PubMed2006

The effect of viewing the moving limb and target object during the early phase of movement on the online control of grasping.

Two experiments were conducted to investigate (1) during which phase of the movement vision is most critical for control, and (2) how vision of the target object and the participant's moving limb affect the control of grasping during that movement phase. In Experiment 1, participants, wearing liquid crystal shutter goggles, reached for and grasped a cylinder with a diameter of 4 or 6 cm under a shutting paradigm (SP) and a re-opening paradigm (RP). In SP, the goggles closed (turned opaque) 0 ms, 150 ms, 350 ms, 500 ms, or 700 ms after movement onset, or remained open (transparent) during the prehension movements. In RP, the goggles closed immediately upon movement onset, and re-opened 0 ms (i.e., without initially shutting), 150 ms, 350 ms, 500 ms, or 700 ms after the initial shutting, or remained opaque throughout the prehension movements. The duration of the prehension movements was kept relatively constant across participants and trials at approximately 1100 ms, i.e., the duration of prehension movements typically observed in daily life. The location of the target object was constant during the entire experiment. The SP and RP paradigms were counter-balanced across participants, and the order of conditions within each session was randomized. The main findings were that peak grip aperture (PGA) in the 150 ms-shutting condition was significantly larger than in the 350 ms-shutting condition, and that PGA in the 350 ms-re-opening condition was significantly larger than in the 150 ms-re-opening condition. These results revealed that online vision between 150 ms and 350 ms was critical for grasp control on PGA in typical, daily-life-speeded prehension movements. Furthermore, the results obtained for the time after maximal deceleration (TAMD; movement duration-time to maximal deceleration) demonstrated that early-phase vision contributed to the temporal pattern of the later movement phases (i.e., TAMD). The results thus demonstrated that online vision in the early phase of movement is crucial for the control of grasping. In addition to the apparatus used in Experiment 1, two liquid shutter plates placed in the same horizontal plane (25 cm above the experimental table) were used in Experiment 2 to manipulate the visibility of the target and the participant's moving limb. The plate closest to the participant altered vision of the limb/hand, while the more distant plate controlled vision of the object. The conditions were as follows: (1) both plates were open during movement (full vision condition); (2) both plates were closed 0, 150, or 350 ms following onset of arm movement (front-rear condition: FR); or (3) only the near plate closed 0, 150, or 350 ms following the onset of the arm movement (front condition: F). The results showed that shutting at 0 and 150 ms in the FR condition caused a significantly larger PGA, while the timing of shutting in the F condition had little influence on the PGA. These findings indicated that online vision, especially of the target object, during the early phase of prehension movements is critical to the control of grasping.

Arm↗
PubMed2003

Mechanisms of differences in gating effects on short-and long-latency somatosensory evoked potentials relating to movement.

We investigated the mechanisms underlying the differences in gating effects on short- and long-latency somatosensory evoked potentials (SEPs) relating to movement. SEPs were recorded in normal subjects for 6 different tasks in Experiment 1: Control, Movement, Distraction, Attention, Movement during Distraction and Movement during Attention, and for 4 different tasks in Experiment 2: Control, Passive Movement, Contralateral Movement and Movement Imagery. The amplitudes of short-latency SEPs were significantly reduced by active and passive movement of the stimulated hand, but long-latency SEPs (N140-P200) were significantly enhanced by active movement of the stimulated hand. Attention, Distraction, Contralateral Movement and Movement Imagery did not affect the amplitudes of SEPs. The degree of enhancement of long-latency SEPs by active Movement was greater than that by active movement with Attention or Distraction. Gating effects on long-latency SEPs were different from those on short-latency SEPs. Since this effect was not related to Attention/Distraction, Passive Movement, Movement Imagery or Movement of another site, it is probably due to specific centrifugal effects, which are different from more direct gating effects on short-latency components. This study showed the difference in gating effects on somatosensory perception depending on time periods following stimulation, which may indicate an interaction between motor and somatosensory cortex.

Adult↗