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PubMed1991

Electromyographic and cinematographic analysis of movement from a kneeling to a standing position in healthy 5- to 7-year-old children.

Physical therapists often use transitional postures such as half-kneeling to help children with movement dysfunction attain an upright posture. Little is known, however, about how healthy children activate lower extremity muscles to move the hip, knee, and ankle joints as they move from kneeling through half-kneeling to stand up against gravity. The purpose of this study was to describe movement from kneeling to standing in 10 healthy 5- to 7-year-old children. Electromyography was used to record the activity of four lower extremity muscles. Cinematography was used to record joint motion of the hip, knee, and ankle of the leg initiating movement, in addition to trajectories of specific anatomical landmarks as the children rose from a kneeling to a standing position. Greater active range of motion of the hip, knee, and ankle was necessary to move from a kneeling to a standing position using the half-kneel transitional posture than is required during normal gait. The activation patterns of the gastrocnemius, tibialis anterior, rectus femoris, and biceps femoris muscles of the leg initiating movement exhibited variability among subjects during the kneel-to-stand movement. Maximum joint range of motion and position of the hip, knee, and ankle joints at specific points in the movement exhibited less variability than patterns of muscle activation. The results showed that movement from a kneeling to a standing position in healthy children is quantifiable and can be used to help determine what normal components of movement are necessary to successfully master this movement against gravity that is antecedent to ambulation. Further studies are needed to investigate antigravity movement in younger children and in children with movement dysfunction to more fully understand normal and abnormal movement in children.

Ankle Joint↗
PubMed1980

The measurement of itch with sensitive limb movement meters.

A sensitive electromagnetic movement detector has been developed to estimate itch by measuring scratch during sleep. The cumulative time of nocturnal limb movements of patients with itchy and non-itchy liver diseases was estimated. Non-itchy patients moved their arms for 24 +/- 9.3 min/8 h (mean +/- s.d.) and their legs for 16 +/- 7.0 min/8 h. The limb movements were not related to left or right handedness or the sex or age of the patient. Itchy patients had increased nocturnal limb movements; however, the increase in arm movement (up to five times control level) was much greater than the increase in leg movement (up to twice control level). The marked increase in arm movements in itchy patients supports the view that this movement is largely due to scratching. The reproducibility of the estimates of arm movements was reasonable (within-person coefficient of variation 22%). In three studies, treatment resulted in a reduction of arm movements to normal levels. The measurement of cumulative nocturnal arm movement by these sensitive meters appears to be a valid estimate of scratch and superior to a subjective assessment of itch. The devices may also be applied to other studies, such as the effects of hypnotic drugs on sleep movement and the measurement of vibration.

Adolescent↗
PubMed1987

Cerebellar neuronal activity related to arm movements in trained rhesus monkeys.

1. The role of the paravermal cerebellum in controlling arm movements in monkeys trained to perform visually guided movements was investigated. Discharge patterns of extracellularly recorded Purkinje, Golgi, nuclear and unidentified cells were correlated with arm position, velocity and acceleration. 2. The discharge of thirty-seven out of fifty-two movement-related Purkinje cells and that of thirty-three out of forty-five other movement-related cerebellar neurones was more highly correlated with limb velocity (0.95 greater than r greater than 0.4) than with position or acceleration. Twelve out of fifty-two Purkinje cells and twelve out of forty-five other cells were related to both limb velocity and limb position. Three Purkinje cells were related to limb acceleration and position and no cell was related to position or acceleration alone. 3. Modulation of discharge of these cells usually preceded movement (range -240 ms, unit leading movement, to +180 ms, unit lagging; mode -36 ms; mean -15 ms). 4. Each movement-related neurone was tested for four directions of movement. All showed a preferred direction in which the correlation with arm movement velocity was highest. However, 43% (30/70) correlated at r greater than 0.4 with movements in a second direction, usually that opposite to their preferred direction. Sixty-three per cent of these neurones fired earlier during movements in the preferred than in the opposite direction. 5. It is concluded that the paravermal cerebellum may be involved in computing the velocity vectors required for achieving properly directed and co-ordinated movements of the whole arm.

Action Potentials↗
PubMed1993

Organization of motor output in slow finger movements in man.

1. Slow finger movements were analysed in normal human subjects with regard to kinematics and EMG activity of the long finger muscles. Surface EMG from the finger extensor and flexor muscles on the forearm was recorded along with angular position and angular velocity during voluntary ramp movements at single metacarpophalangeal joints. Angular acceleration was computed from the velocity record. 2. It was found that movements were not smooth but characterized by steps or discontinuities, often recurring at intervals of 100-125 ms, yielding velocity and acceleration profiles dominated by 8-10 Hz cycles. The discontinuities were manifest from the very first trial and thus not dependent on training. Their amplitude and amount varied between subjects but were relatively stable for the individual subject. 3. The 8-10 Hz cycles were seen with voluntary ramp movements of widely varying velocities, higher velocities being associated with larger steps recurring with the same repetition rate as the small steps of slow voluntary ramps. Maximal step amplitude observed was more than one order of magnitude larger than physiological tremor. 4. The individual 8-10 Hz cycle was asymmetrical in that decelerations usually reached higher peaks than the preceding acceleration, suggesting that the antagonist contributed with a braking action. Moreover, in very slow voluntary ramps, the movement cycles were often interspaced by periods of zero velocity, providing a highly non-sinusoidal velocity profile. 5. The EMG of the agonist and the antagonist muscles was modulated in close relation to the accelerations and decelerations respectively of the individual movement cycle. These modulations were present in both extensor and flexor muscles, although they were more consistent and usually more prominent in the former. 6. The findings indicate that a feature of slow finger movements was an 8-10 Hz periodic output to the muscular system, suggesting that slow finger movements are implemented by a series of biphasic force pulses, involving not only the shortening agonist muscle propelling the movement, but the antagonist muscle as well whose activity increased shortly after the agonist and contributed to a sharp deceleration of the individual step of movement. 7. It is proposed, as a hypothesis, that this biphasic motor output may reflect a similar organization of the descending motor command for slow finger movements. Hence, this command would include a series of biphasic pulses, concatenated at a rate of 8-10 per second and a pulse-height regulator capable of setting the size of the pulse and thus the overall speed of the movement.

Adult↗
PubMed2005

Olivocerebellar modulation of motor cortex ability to generate vibrissal movements in rat.

The vibrissal movements known as whisking are generated in a pulsatile, or non-continuous, fashion and comprise sequences of brief regularly spaced movements. These rhythmic timing sequences imply the existence of periodically issued motor commands. As inferior olivary (IO) neurones generate periodic synchronous discharges that could provide the underlying timing signal, this possibility was tested by determining whether the olivocerebellar system modulates motor cortex (MCtx)-triggered whisker movements in rats. Trains of current pulses were applied to MCtx, and the resulting whisker movements were recorded using a high speed video camera. The evoked movement patterns demonstrated properties consistent with the existence of an oscillatory motor driving rhythm. In particular, movement amplitude showed a bell-shaped dependence on stimulus frequency, with a peak at 11.5+/-2.3 Hz. Moreover, movement trajectories showed harmonic and subharmonic entrainment patterns within specific stimulus frequency ranges. By contrast, movements evoked by facial nerve stimulation showed no such frequency-dependent properties. To test whether the IO was the oscillator in question, IO neuronal properties were modified in vivo by intra-IO picrotoxin injection, which enhances synchronous oscillatory IO activity and reduces its natural frequency. The ensuing changes in the evoked whisker patterns were consistent with these pharmacological effects. Furthermore, in cerebellectomized rats, oscillatory modulation of MCtx-evoked movements was greatly reduced, and intra-IO picrotoxin injections did not affect the evoked movement patterns. Additionally, multielectrode recording of Purkinje cell complex spikes showed a temporal correlation of olivocerebellar activity during MCtx stimulus trains to evoked movement patterns. In sum, the results indicate that MCtx's ability to generate movements is modulated by an oscillatory signal arising in the olivocerebellar system.

Animals↗
PubMed2001

Planning reaching and grasping movements: the problem of obstacle avoidance.

In this article, we review a model of the movement-planning processes that people use for direct reaching, reaching around obstacles, and grasping, and we present observations of subjects' repeated movements of the hand to touch 2 target locations, circumventing an intervening obstacle. The model defines an obstacle as a posture that, if adopted, would intersect with any part of the environment (including the actor himself or herself). The model finds a trajectory that is likely to bring the end-effector to the target by means of a one-or two- stage planning process. Each stage exploits the principles of instance retrieval and instance generation. In the first stage, a goal posture is identified, and the trajectory of a direct transition to that posture is tested for collision. If the direct movement has no collision, the movement to the target is immediately executed in joint space. If, however, the direct movement is foreseen to result in a collision, a second planning stage is invoked. The second planing stage identifies a via posture, movement through which will probably avoid the collision. Movement to and from the via posture is then superimposed on the main movement to the target so that the combined movement reaches the target without colliding with intervening obstacles. We describe the details of instance retrieval and instance generation for each of these planning stages and compare the model's performance with the observed kinematics of direct movements as well as movements around an obstacle. Then we suggest how the model might contribute to the study of movements in people with motor disorders such as spastic hemiparesis.

Adult↗
PubMed2005

Speed, amplitude, and asymmetry of lip movement in voluntary puckering and blowing expressions: implications for facial assessment.

The context of voluntary movement during facial assessment has significant effects on the activity of facial muscles. Using automated facial analysis, we found that healthy subjects instructed to blow produced lip movements that were longer in duration and larger in amplitude than when subjects were instructed to pucker. We also determined that lip movement for puckering expressions was more asymmetric than lip movement in blowing. Differences in characteristics of lip movement were noted using facial movement analysis and were associated with the context of the movement. The impact of the instructions given for voluntary movement on the characteristics of facial movement might have important implications for assessing the capabilities and deficits of movement control in individuals with facial movement disorders. If results generalize to the clinical context, assessment of generally focused voluntary facial expressions might inadequately demonstrate the full range of facial movement capability of an individual patient.

Adult↗
PubMed1990

Disturbances in human arm movement trajectory due to mild cerebellar dysfunction.

The temporal structure of arm movements was studied in nine cerebellar patients with mild impairment of the upper limbs and in six age-matched control subjects. The experimental paradigm consisted of visually guided, step tracking movements about the elbow. Movements ranged from 10 degrees to 70 degrees in amplitude and were made under different instructions (fast, fast/accurate, accurate). As in normal subjects, cerebellar patients were able to scale peak velocity with movement amplitude. This relationship was highly linear under all instruction conditions. Similar relationships existed between movement duration and amplitude. In contrast to normal subjects who produced movements with nearly symmetric velocity profiles, movements made by cerebellar patients were characterised by short acceleration and long deceleration durations. The degree of asymmetry was directly related to movement duration but was unaffected by movement peak velocity. Acceleration durations did not increase beyond 300 ms even in movements lasting up to 1s. These findings demonstrate that, despite little or no obvious impairment of the limb during routine examination, the temporal structure of voluntary movements in cerebellar patients is clearly disturbed. This supports the view that the production of an optimal movement trajectory is under cerebellar influence.

Adult↗
PubMed1995

Control variables and proprioceptive feedback in fast single-joint movement.

Sensorimotor mechanisms were studied on the basis of kinematic and electromyographic data as well as the static torque developed by the muscles as a function of joint angle. The latter relationship is known as the torque/angle characteristic. Fast single-joint movement may result from a shift in this characteristic and a change in its slope. Such movements were studied at the wrist in 9 normal and 1 deafferented subject. After training to flex the wrist to a target, subjects repeated the same movements but in random test trials movements were opposed by the load generated by linear position feedback to a torque motor. At the end of the loaded trials, the load was suddenly removed. In the second experiment, subjects made wrist movements to the target that were opposed by the load and, on random test trials, the movements were not loaded. In these test trials, the wrist arrived in a static position outside the target zone. In both experiments, subjects were instructed not to correct errors. The final torque/angle characteristics specified in the movements were reconstructed on the basis of the static wrist positions and torques before and after unloading. Normal subjects made movements by shifting the position of the torque/angle characteristic and by increasing its slope. If subjects indeed maintained the same pattern of control variables (descending commands), the same final position of the characteristic would be reproduced from trial to trial regardless of load perturbations. This assumption of equifinality was tested by comparing the final position of the wrist in nonloaded movements with that after removal of the load in loaded movements. Equifinality was observed in normal subjects. Movements in the deafferented subject were also associated with a shift of the torque/angle characteristic and a change in its slope. However, she was unable to consistently reproduce its final position. In spite of muscle coactivation, her maximal stiffness was lower than in normal subjects. In the absence of vision, the subject made movements with the load by increasing the slope of the characteristic instead of by shifting its position far enough. Load perturbation affected her final wrist position (inequifinality), which may reflect the presence of a significant hysteresis of the characteristic as a result of the absence of stretch reflexes. The deficits following deafferentation presumably result from the destruction of biomechanical and sensorimotor mechanisms including the ability of control variables to specify the positional frame of reference for afferent and descending systems.

Adult↗
PubMed2003

Coordinated turn-and-reach movements. II. Planning in an external frame of reference.

The preceding study demonstrated that normal subjects compensate for the additional interaction torques generated when a reaching movement is made during voluntary trunk rotation. The present paper assesses the influence of trunk rotation on finger trajectories and on interjoint coordination and determines whether simultaneous turn-and-reach movements are most simply described relative to a trunk-based or an external reference frame. Subjects reached to targets requiring different extents of arm joint and trunk rotation at a natural pace and quickly in normal lighting and in total darkness. We first examined whether the larger interaction torques generated during rapid turn-and-reach movements perturb finger trajectories and interjoint coordination and whether visual feedback plays a role in compensating for these torques. These issues were addressed using generalized Procrustes analysis (GPA), which attempts to overlap a group of configurations (e.g., joint trajectories) through translations and rotations in multi-dimensional space. We first used GPA to identify the mean intrinsic patterns of finger and joint trajectories (i.e., their average shape irrespective of location and orientation variability in the external and joint workspaces) from turn-and-reach movements performed in each experimental condition and then calculated their curvatures. We then quantified the discrepancy between each finger or joint trajectory and the intrinsic pattern both after GPA was applied individually to trajectories from a pair of experimental conditions and after GPA was applied to the same trajectories pooled together. For several subjects, joint trajectories but not finger trajectories were more curved in fast than slow movements. The curvature of both joint and finger trajectories of turn-and-reach movements was relatively unaffected by the vision conditions. Pooling across speed conditions significantly increased the discrepancy between joint but not finger trajectories for most subjects, indicating that subjects used different patterns of interjoint coordination in slow and fast movements while nevertheless preserving the shape of their finger trajectory. Higher movement speeds did not disrupt the arm joint rotations despite the larger interaction torques generated. Rather, subjects used the redundant degrees of freedom of the arm/trunk system to achieve similar finger trajectories with differing joint configurations. We examined finger movement patterns and velocity profiles to determine the frame of reference in which turn-and-reach movements could be most simply described. Finger trajectories of turn-and-reach movements had much larger curvatures and their velocity profiles were less smooth and less bell-like in trunk-based coordinates than in external coordinates. Taken together, these results support the conclusion that turn-and-reach movements are controlled in an external frame of reference.

Acceleration↗
PubMed2003

Neural control of rhythmic human arm movement: phase dependence and task modulation of hoffmann reflexes in forearm muscles.

Although we move our arms rhythmically during walking, running, and swimming, we know little about the neural control of such movements. Our working hypothesis is that neural mechanisms controlling rhythmic movements are similar in the human lumbar and cervical spinal cord. Thus reflex modulation during rhythmic arm movement should be similar to that seen during leg movement. Our main experimental hypotheses were that the amplitude of H-reflexes in the forearm muscles would be modulated during arm movement (i.e., phase-dependent) and would be inhibited during cycling compared with static contraction (i.e., task-dependent). Furthermore, to determine the locus of any modulation, we tested the effect that active and passive movement of the ipsilateral (relative to stimulated arm) and contralateral arm had on H-reflex amplitude. Subjects performed rhythmic arm cycling on a custom-made hydraulic ergometer in which the two arms could be constrained to move together (180 degrees out of phase) or could rotate independently. Position of the stimulated limb in the movement cycle is described with respect to the clock face. H-reflexes were evoked at 12, 3, 6, and 9 o'clock positions during static contraction as well as during rhythmic arm movements. Reflex amplitudes were compared between tasks at equal M wave amplitudes and similar levels of electromyographic (EMG) activity in the target muscle. Surface EMG recordings were obtained bilaterally from flexor carpi radialis as well as from other muscles controlling the wrist, elbow, and shoulder. Compared with reflexes evoked during static contractions, movement of the stimulated limb attenuated H-reflexes by 50.8% (P < 0.005), 65.3% (P < 0.001), and 52.6% (P < 0.001) for bilateral, active ipsilateral, and passive ipsilateral movements, respectively. In contrast, movement of the contralateral limb did not significantly alter H-reflex amplitude. H-reflexes were also modulated by limb position (P < 0.005). Thus task- and phase-dependent modulation were observed in the arm as previously demonstrated in the leg. The data support the hypothesis that neural mechanisms regulating reflex pathways in the moving limb are similar in the human upper and lower limbs. However, the inhibition of H-reflex amplitude induced by contralateral leg movement is absent in the arms. This may reflect the greater extent to which the arms can be used independently.

Adult↗
PubMed2003

The role of execution noise in movement variability.

The origin of variability in goal-directed movements is not well understood. Variability can originate from several neural processes such as target localization, movement planning, and movement execution. Here we examine variability resulting from noise in movement execution. In several experiments, subjects moved their unseen hand to visual targets, under conditions which were designed to minimize the variability expected from localization and planning processes. We tested short movements in 32 directions in a center-out reaching task. The variability in the movement endpoints and in the initial movement direction varied systematically with the movement direction, with some directions having up to twice the variability of others. In a second experiment we tested four movements in the same direction but with different extents. Here, the longer movements were systematically curved, and the endpoint ellipses were not aligned with the straight line between starting and end position, but they were roughly aligned with the last part of the trajectory. We show that the variability observed in these experiments cannot be explained by planning noise but is well explained by noise in movement execution. A combination of both signal-dependent and signal-independent noise in the amplitude of the motor commands and temporal noise in their duration can explain the observed variability. Our results suggest that, in general, execution noise accounts for at least a large proportion of movement variability.

Adolescent↗
PubMed2002

Neuronal activity related to the visual representation of arm movements in the lateral cerebellar cortex.

Testing the hypothesis that the lateral cerebellum forms a sensory representation of arm movements, we investigated cortical neuronal activity in two monkeys performing visually guided step-tracking movements with a manipulandum. A virtual target and cursor image were viewed co-planar with the manipulandum. In the normal task, manipulandum and cursor moved in the same direction; in the mirror task, the cursor was left-right reversed. In one monkey, 70- and 200-ms time delays were introduced on cursor movement. Significant task-related activity was recorded in 31 cells in one animal and 142 cells in the second: 10.2% increased activity before arm movements onset, 77.1% during arm movement, and 12.7% after the new position was reached. To test for neural representation of the visual outcome of movement, firing rate modulation was compared in normal and mirror step-tracking. Most task-related neurons (68%) showed no significant directional modulation. Of 70 directionally sensitive cells, almost one-half (n = 34, 48%) modulated firing with a consistent cursor movement direction, many fewer responding to the manipulandum direction (n = 9, 13%). For those "cursor-related" cells tested with delayed cursor movement, increased activity onset was time-locked to arm movement and not cursor movement, but activation duration was extended by an amount similar to the applied delay. Hence, activity returned to baseline about when the delayed cursor reached the target. We conclude that many cells in the lateral cerebellar cortex signaled the direction of cursor movement during active step-tracking. Such a predictive representation of the arm movement could be used in the guidance of visuo-motor actions.

Action Potentials↗
PubMed1990

Activity of identified wrist-related pallidal neurons during step and ramp wrist movements in the monkey.

1. The activity of globus pallidus (GP) neurons (n = 1,117) was studied in two monkeys to reexamine the relation of neuronal activity to movement type (slow vs. fast) while they performed both a visually guided step and ramp wrist tracking task. To select neurons specifically related to wrist movements, we employed both a somatosensory examination of individual body parts and a statistical analysis of the strength of temporal coupling of neuronal discharges to active wrist movement. 2. Neuronal responses to somatosensory stimulation were studied in 1,000 high-frequency GP neurons, of which 686 exhibited clear responses to manipulation of body parts. Of the latter, 336 responded to passive manipulation of forelimb joints and 58 selectively to passive flexion or extension of the wrist. 3. In the external segment of GP (GPe), most neurons responding to passive wrist movement were found to be clustered in four to five adjacent, closely positioned (separated by 200 microns) tracks in single coronal planes. The clusters were irregular in shape with a maximal width of 800-1,000 microns. Separate clusters of neurons responsive to passive wrist movement were identified in planes 3 mm apart in one monkey and in planes 500 microns apart in the other. Multiple clusters of neurons were also found for neurons responsive to joints other than the wrist. These findings suggest a more discrete and complex representation of individual joints in the primate GP than previously conceived. 4. During the performance of the wrist flexion and extension task, 92 neurons showed clear and consistent changes in activity. For these neurons we measured, with a statistical method on a trial-by-trial basis, the strength of temporal coupling between the onset of active wrist movement and the onset of change in neuronal discharge rate. Fifteen neurons showed changes in activity time-locked to the onset of active wrist movement. 5. Twelve pallidal neurons were classified as "wrist-related" based on their movement-locked changes in discharge during task performance and their clear responses to passive wrist joint rotation on examination. All of these neurons exhibited statistically significant modulation of their discharge rate during both fast (peak velocity 97-205 degrees/s) and slow (peak velocity 20-62 degrees/s) wrist movements in the task. The amplitudes of modulation were larger during fast wrist movement than slow movement. These results suggest that the basal ganglia motor circuit plays a similar, rather than an exclusive, role in the control of slow and fast limb movements.

Animals↗
PubMed1992

Dynamic properties of medial rectus motoneurons during vergence eye movements.

1. An early study by Keller reported that medial rectus motoneurons display a step change in firing rate during accommodative vergence movements. However, a later study by Mays and Porter reported gradual changes in firing rate during symmetrical vergence movements. Furthermore, subsequent inspection of the activity of individual medial rectus motoneurons during vergence movements indicated transient changes in their firing rate that had not been noted by Mays and Porter. For conjugate eye movements, in addition to a position signal, motoneurons display an eye velocity signal that compensates for the characteristics of the oculomotor plant. This suggested that the transient change in firing rate seen during vergence movements represented a velocity signal. Therefore the present study used single-unit recording techniques in alert rhesus monkeys to examine the dynamic behavior of medial rectus motoneurons during vergence eye movements. 2. The relationship between firing rate and eye velocity was first studied for vergence responses to step changes in binocular disparity and accommodative demand. Inspection of single trials showed that medial rectus motoneurons display transient changes in firing rate during vergence eye movements. To better visualize the dynamic signal during vergence movements, an expected firing rate (eye position multiplied by position sensitivity of the cell plus its baseline firing rate) was subtracted from the actual firing rate to yield a difference firing rate, which was displayed along with the eye velocity trace for individual trials. During all smooth symmetrical vergence movements, the profile of the difference firing rate very closely resembled the velocity profile. 3. To quantify the relationship between eye velocity and firing rate, two approaches were taken. In one, peak eye velocity was plotted against the difference firing rate. This plot yielded a measure of the velocity sensitivity of the cell (prv). In the other, a scatter plot was produced in which horizontal eye velocity throughout the vergence eye movement was plotted against the difference firing rate. This plot yielded a second measure of the velocity sensitivity of the cell (rv). 4. The behavior of 10 cells was studied during both sinusoidal vergence tracking and conjugate smooth pursuit over a range of frequencies from 0.125 to 1.0 Hz. This enabled the frequency sensitivity of the medial rectus motoneurons to be assessed for both types of movements. Both vergence velocity sensitivity and smooth pursuit velocity sensitivity decreased with increasing frequency. This is similar to a finding by Fuchs and co-workers for lateral rectus motoneurons during smooth pursuit eye movements.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Purkinje cell complex and simple spike changes during a voluntary arm movement learning task in the monkey.

1. To evaluate the role of the cerebellum during improvement of voluntary motor performance over time, the discharge of 88 Purkinje cells in the intermediate and lateral cerebellum of two primates (Macaca mulatta) was investigated during a motor learning task involving visually guided arm movements. The animals were trained to move a draftsman's style manipulandum over a horizontally placed video screen. The animals were required to move a cursor from the start box to one of four target boxes by movement of the manipulandum. Errors were introduced into the movement by altering the visual feedback loop, changing the gain between the cursor movement and the hand movement. When a novel gain was presented over 100-200 movement trials, the animals adapted the movements to the new gain. The animals used a strategy of scaling the amplitude and velocity of the initial phase of the movement while keeping the time to peak velocity constant. 2. The learning paradigm consisted of an initial control phase with 35-100 trials at the gain of 1.0. The next 100-200 trials, the learning phase, were presented at one of four gains (0.6, 0.75, 1.5, 2.0). Lastly, a testing phase involved 80% of 100 trials at the learned gain and 20% of the trials randomly interspersed at the control gain of 1.0. An additional "distance control" was used in most experiments to control for the movement scaling associated with learning. In this series of movements using a gain of 1.0, the target box was placed at the distance and direction the hand would have to move in the adapted state. Two aspects of the kinematics were the same for the distance control and the movement at the learned gain: movement amplitude and time to peak velocity. There were, however, slight differences in the peak velocity attained. For gains < 1.0, the peak velocity of the learned task was 14-20% lower than the distance controls, and for gains > 1.0, it was 10-18% higher. 3. After implantation of chronic unit recording hardware, Purkinje cell simple and complex spike discharge was recorded extracellularly during the learning task. The cells were located primarily in the ipsilateral intermediate zone or nearby hemisphere of lobules V and VI. Simple and complex spike histograms, as well as averages of the hand displacement and velocity profiles, were calculated for each phase of the paradigm. To determine the time course of any changes, the learning trials were subdivided into three equal phases.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1995

Impairments of reaching movements in patients without proprioception. II. Effects of visual information on accuracy.

1. The aim of this study was to determine how vision of a cursor indicating hand position on a computer screen or vision of the limb itself improves the accuracy of reaching movements in patients deprived of limb proprioception due to large-fiber sensory neuropathy. In particular, we wished to ascertain the contribution of such information to improved planning rather than to feedback corrections. We analyzed spatial errors and hand trajectories of reaching movements made by subjects moving a hand-held cursor on a digitizing tablet while viewing targets displayed on a computer screen. The errors made when movements were performed without vision of their arm or of a screen cursor were compared with errors made when this information was available concurrently or prior to movement. 2. Both monitoring the screen cursor and seeing their limb in peripheral vision during movement improved the accuracy of the patients' movements. Improvements produced by seeing the cursor during movement are attributable simply to feedback corrections. However, because the target was not present in the actual workspace, improvements associated with vision of the limb must involve more complex corrective mechanisms. 3. Significant improvements in performance also occurred in trials without vision that were performed after viewing the limb at rest or during movements. In particular, prior vision of the limb in motion improved the ability of patients to vary the duration of movements in different directions so as to compensate for the inertial anisotropy of the limb. In addition, there were significant reductions in directional errors, path curvature, and late secondary movements. Comparable improvements in extent, direction, and curvature were produced when subjects could see the screen cursor during alternate movements to targets in different directions. 4. The effects of viewing the limb were transient and decayed during a period of minutes once vision of the limb was no longer available. 5. It is proposed that the improvements in performance produced after vision of the limb were mediated by the visual updating of internal models of the limb. Vision of the limb at rest may provide configuration information while vision of the limb in motion provides additional dynamic information. Vision of the cursor and the resulting ability to correct ongoing movements, however, is considered primarily to provide information about the dynamic properties of the limb and its response to neural commands.

Adult↗
PubMed1996

Changes in the control of arm position, movement, and thalamic discharge during local inactivation in the globus pallidus of the monkey.

1. To examine the effect of disruption of basal ganglia output on limb stability and movement, muscimol was injected into the internal globus pallidus (GPi) of monkeys trained to make arm movements to visible or remembered targets in a two-dimensional workspace. 2. Injections of as little as 0.25 micrograms muscimol at GPi sites at which pallidal neurons with arm movement activity had been recorded were followed by drift of the contralateral arm within < 10 min. Drift was usually in the flexor direction. Injections at a few sites in or near the external pallidal segment sometimes were followed by extensor drift. 3. Drift was active (accompanied by activation of agonist muscles), but could be overcome by the animal, resulting in an oscillating movement off and on the required position. 4. The pallidal-receiving (PR) area of the thalamus was identified by recording the response of thalamic neurons to stimulation in the globus pallidus. The activity of 15 neurons identified as PR cells (n = 6) or within the PR region was recorded both before and after injection of muscimol into GPi. After the injection, the tonic discharge increased during the hold period in 47% of the cells studied. When postural drift also occurred, there was a close temporal correlation between the postinjection time at which drift occurred and the time at which the tonic discharge rate increased in thalamic neurons that were clearly related to arm movement. 5. The peak velocity of arm movements to visible or remembered visual target locations was decreased after injection of muscimol into GPi, sometimes with an increase in movement time. 6. The firing rate of PR thalamic neurons after injection of muscimol was also increased during the perimovement period. Because of the increase in the tonic discharge rate, however, the phasic movement-related change in activity could stay the same or even decrease. Postinjection changes in this movement-related phasic activity, however, were not necessarily coincident with changes in peak movement velocity. 7. Changes in reaction time were variable after injection of muscimol. In some cases it was increased, and in others decreased. The time of onset of phasic movement-related changes in the activity of PR neurons studied was not altered by the injection. 8. Our data indicate that the tonic inhibitory output of GPi, in particular to the cortical motor areas, is especially important in the maintenance of postural stability. In the absence of normal pallidal output, desired limb position can be achieved on the basis of either current or prior visual cues, but targeted movements are slowed.

Animals↗