Search PubMed⌕ Search

Biomedical subjects

J D Cooke

Publications and source records attributed to J D Cooke.

At least 19 recordsLinked to original sources
PubMed1998

Sinusoidal forearm tracking with delayed visual feedback. I. Dependence of the tracking error on the relative delay.

During forearm tracking of a sinusoidally moving target matching of proprioceptive and visual feedback was altered by introducing different visual delays. In five normal subjects seven target frequencies were tested ranging from 0.3 to 1.5 Hz. For each target frequency nine different delays were used ranging from 0 to 120% of the cycle duration with target frequency and delay being varied randomly. Tracking error revealed a cyclic behaviour with an increase up to delays of about 50% of the target cycle duration and an improvement for delays larger than 50%. Modulation of response frequency was less pronounced compared with tracking error variation but also was dependent on relative phase. The response frequency matched the target frequency at delays of 0 and 100% of cycle duration and was slightly lower than the target frequency with relative delays of about 50%. The introduction of a visual delay during sinusoidal forearm tracking leads to a spatial in addition to the temporal mismatch between proprioception and vision. The temporal and the spatial incompatibility influence the tracking performance differentially.

Adult↗
PubMed1996

Motor unit activity during human single joint movements.

1. To explore the neural control of single joint movements in humans, the activity of 47 motor units in triceps brachii muscle was recorded during elbow flexion and extension movements. Movements were performed with different but changing deceleration magnitudes, while the acceleration magnitude was kept constant, to determine the relationship between motor unit activity and the acceleration and deceleration characteristics of single joint movements. 2. The number of motor unit action potentials was found to vary with the magnitude of the movement deceleration. In addition the duration of the discharge of a motor unit was found to parallel the duration of the acceleration phase of the movement, when the acceleration duration was varied while acceleration magnitude was kept constant. 3. Approximately half of the recorded motor units in triceps brachii were active both in the initiation and in the termination of the extension movements. However, motor units were identified that participated in specific phases of the movement (i.e., either during the 1st agonist or 2nd agonist burst of muscle activity) depending on the magnitude of the acceleration or deceleration. 4. During flexion movements, when the triceps muscle served as an antagonist, approximately half of the motor units were recruited only when the magnitude of the flexion deceleration was large. Further, this deceleration magnitude was larger than that evident during the extension movements in which the motor unit discharged. 5. The findings of this study demonstrate that the nervous system activates the same motor units whether the muscle is functioning as an agonist or antagonist so as to control the characteristics of acceleration and deceleration of single joint movements.

Acceleration↗
PubMed1996

Basal ganglia and cerebellar impairment differentially affect the amplitude and time scaling during the performance of forearm step tracking movements.

Forearm step tracking movements of different amplitudes were analysed in nine patients with cerebellar and five patients with parkinsonian symptoms in comparison to six normal subjects. Movements were made under two instructions: 1) track "as fast as possible" and 2) "as precisely as possible". Movement duration, acceleration duration and peak velocity increased with increasing amplitude. The ratio between acceleration and deceleration duration was independent of movement amplitude in the parkinsonian patients and the normal subjects. In the cerebellar patients, however, this ratio decreased with increasing amplitude. This impairment of the relative timing between acceleration and deceleration duration implies that, in contrast to parkinsonian patients, cerebellar patients cannot anymore utilize physiological scaling mechanisms when performing movements of different amplitudes.

Adult↗
PubMed1995

Reprogramming of muscle activation patterns at the wrist in compensation for elbow reaction torques during planar two-joint arm movements.

The relationship between wrist kinematics, dynamics and the pattern of muscle activation were examined during a two-joint planar movement in which the two joints moved in opposite directions, i.e. elbow flexion/wrist extension and elbow extension/wrist flexion. Elbow movements (ranging from 10 to 70 deg) and wrist movements (ranging from 10 to 50 deg) were performed during a visual, step-tracking task in which subjects were required to attend to the initial and final angles at each joint. As the elbow amplitude increased, wrist movement duration increased and the wrist movement trajectories became quite variable. Analysis of the torques acting at the wrist joint showed that elbow movements produced reaction torques acting in the same direction as the intended wrist movement. Distinct patterns of muscle activation were observed at the wrist joint that were dependent on the relative magnitude of the elbow reaction torque in relation to the net wrist torque. When the magnitude of the elbow reaction torque was quite small, the wrist agonist was activated first. As the magnitude of the elbow reaction torque increased, activity in the wrist agonist decreased significantly. In conditions where the elbow reaction torque was much larger than the net wrist torque, the wrist muscle torque reversed direction to oppose the intended movement. This reversal of wrist muscle torque was directly associated with a change in the pattern of muscle activation where the wrist antagonist was activated prior to the wrist agonist. Our findings indicate that motion of the elbow joint is an important consideration in planning wrist movement. Specifically, the selection of muscle activation patterns at the wrist is dependent on the relative magnitude and direction of the elbow reaction torque in relation to the direction of wrist motion.

Animals↗
PubMed1995

Influence of joint interactional effects on the coordination of planar two-joint arm movements.

We have examined EMG-movement relations in two-joint planar arm movements to determine the influence of interactional torques on movement coordination. Explicitly defined combinations of elbow movements (ranging from 20 to 70 degrees) and wrist movements (ranging from 20 to 40 degrees) were performed during a visual, step-tracking task in which subjects were specifically required to attend to the initial and final angles at each joint. In all conditions the wrist and elbow rotated in the same direction, that is, flexion-flexion or extension-extension. Elbow movement kinematics were only slightly influenced by motion about the wrist. In contrast, the trajectory of the wrist movement was significantly influenced by uncompensated reaction torques resulting from movement about the elbow joint. At any given wrist amplitude, wrist movement duration increased and peak velocity decreased as elbow amplitude increased. In addition, as elbow amplitude increased, wrist movement onset was progressively delayed relative to this elbow movement. Surprisingly, the changes between joint movement onsets were not accompanied by corresponding changes between agonist EMG onsets at the elbow and wrist joints. The mean difference in onset times between elbow and wrist agonists (22-30 ms) remained unchanged across conditions. In addition, a basic pattern of muscle activation that scaled with movement amplitude was observed at each joint. Phasic agonist activity at the wrist and elbow joints remained remarkably similar across conditions and thus the changes in joint movement onset could not be attributed to changes in the motor commands.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Lack of task-related motor unit activity in human triceps brachii muscle during elbow movements.

Surface electromyographic (EMG) recordings have been associated with the acceleration and deceleration characteristics of single joint elbow movements [J. Neurophysiol., 63 (1990) 465-472]. To explore further the neural control of single joint movements, we investigated the behavior of motor units in triceps brachii muscle during elbow flexion and extension movements. In this communication, we provide evidence that individual motor units can contribute to each of the surface EMG bursts. This finding suggests that the nervous system can use the same motor units during movement regardless of whether the muscle is acting as an agonist or antagonist or functioning to initiate or terminate the movement.

Adult↗
PubMed1994

Movement-related phasic muscle activation. III. The duration of phasic agonist activity initiating movement.

To test the hypothesis that phasic muscle activation is related to the acceleration-deceleration characteristics of the resulting movement, we examined the relation between the duration of the acceleratory phase of a variety of movement types and the duration of the phasic muscle activity producing the acceleration (the initial agonist burst, AG1). Movements of five types were studied: (1) step-tracking movements of different amplitudes (10-90 deg) and durations (200-800 ms), (2) movements of the same amplitude (40 deg) and duration (600 ms) varying only in their symmetry ratio (SR, ratio of acceleration to deceleration durations), (3) movements in which acceleration duration was changed while acceleration magnitude was held constant, (4) oscillatory movements of different frequencies and peak amplitudes, (5) step-tracking movements against different inertial loads. Subjects made movements about the elbow joint in the horizontal plane. Surface electromyographic (EMG) activity was recorded from the biceps and the lateral head of the triceps muscles. Under all movement conditions tested and with acceleration duration ranging from 100 to 500 ms, acceleration duration varied linearly with the duration of AG1. Correlation coefficients for the linear regression lines ranged from 0.8 to 0.99. The slope of the best fit linear regression lines ranged from 0.5 to 1.6 and tended to be higher for extensions than flexions. The variations in slope may arise from differing mechanical properties of the biceps and triceps muscles, as well as from active forces produced in the antagonist. AG1 duration was unchanged by inertial loading when subjects kept acceleration duration constant. If subjects responded to an increase in inertial load with an increase in acceleration duration, there was a corresponding increase in AG1 duration. The data demonstrate a general relation between one characteristic of muscle activation (AG1 duration) and the resulting movement. The linear form of the relation is invariant across movement amplitude (range 10-90 deg), speed, duration (range 200-800 ms) and temporal profile (SR range 0.3-2.7), and is also independent of movement type (step, oscillatory). Such a general and simple relation between EMG and movement suggests that, at least to a first approximation, the nervous system can rather simply determine the muscle activation patterns needed to produce movements with desired characteristics.

Acceleration↗
PubMed1994

Effects of gravitational forces on single joint arm movements in humans.

We have examined the kinematics and muscle activation patterns of single joint elbow movements made in the vertical plane. Movements of different amplitudes were performed during a visual, step-tracking task. By adjusting shoulder position, both elbow flexion and extension movements were made under three conditions: (a) in the horizontal plane, (b) in the vertical plane against gravity, and (c) in the vertical plane with gravity. Regardless of the gravitational load, all movements were characterized by time symmetric velocity profiles. In addition, no differences were found in the relationships between movement duration, peak velocity, and movement amplitude in movements with or against gravity. The pattern of muscle activation was influenced however, by the gravitational load. Both flexion and extension movements made with gravity were characterized by a reciprocally organized pattern of muscle activity in which phasic agonist activity was followed by phasic antagonist activity. Flexion and extension movements made against gravity were characterized by early phasic antagonist activity occurring at about the same time as the initial agonist burst. These findings suggest that EMG patterns are modified in order to preserve a common temporal structure in the face of different gravitational loads.

Adult↗
PubMed1993

Role of the cerebellum in visuomotor coordination. I. Delayed eye and arm initiation in patients with mild cerebellar ataxia.

The initiation of coupled eye and arm movements was studied in six patients with mild cerebellar dysfunction and in six age-matched control subjects. The experimental paradigm consisted of 40 deg step-tracking elbow movements made under different feedback conditions. During tracking with the eyes only, saccadic latencies in patients were within normal limits. When patients were required to make coordinated eye and arm movements, however, eye movement onset was significantly delayed. In addition, removal of visual information about arm versus target position had a pronounced differential effect on movement latencies. When the target was extinguished for 3 s immediately following a step change in target position, both eye and arm onset times were further prolonged compared to movements made to continuously visible targets. When visual information concerning arm position was removed, onset times were reduced. Eye and arm latencies in control subjects were unaffected by changes in visual feedback. The results of this study clearly demonstrate that, in contrast to earlier reports of normal saccadic latencies associated with cerebellar dysfunction, initiation of both eye and arm movements is prolonged during coordinated visuomotor tracking thus supporting a coordinative role for the cerebellum during oculo-manual tracking tasks.

Adult↗
PubMed1990

Movement-related phasic muscle activation. I. Relations with temporal profile of movement.

1. The role of phasic muscle activation in determining the temporal properties of human arm movements was studied. The experiments show that subjects can modulate the triphasic electromyographic (EMG) pattern to produce movements of varied temporal structures. 2. Subjects performed horizontal forearm movements in which they varied movement accelerations and decelerations. All movements were of the same amplitude, duration, and peak velocity. A phase-plane (velocity vs. position) template of the desired movement was presented to the subject, who had to reproduce the template by appropriate movement of the forearm. 3. The ratio of the durations of acceleration to deceleration (termed the symmetry ratio, SR) was used as a measure of the temporal structure of the movements. Movements with SRs ranging from 0.4 (short acceleration-long deceleration) to 2.0 (long acceleration-short deceleration) were studied. 4. Subjects modulated the components of the triphasic EMG pattern to produce movements with different temporal profiles. As the SR was increased (increasing acceleration duration-decreasing deceleration duration), the following changes occurred: 1) the duration of the initial agonist burst (AG1) increased while its magnitude decreased; 2) the antagonist burst (ANT1) was progressively delayed relative to movement onset. ANT1 magnitude increased while its duration remained constant; and 3) the magnitude of the second agonist burst (AG2) increased and its duration decreased. 5. The triphasic EMG pattern can be modified to produce movements whose velocity profiles are not the same under simple scaling of duration or magnitude. It is concluded that previously described relations between components of the triphasic EMG pattern and movement parameters, such as amplitude, speed, and duration, are secondary to associated changes in their acceleration and deceleration characteristics.

Acceleration↗
PubMed1990

Movement-related phasic muscle activation. II. Generation and functional role of the triphasic pattern.

1. Electromyographic (EMG) activity of arm movements made at constant velocity was studied in humans. In these movements, acceleration was temporally separated from deceleration by a period of constant velocity (zero acceleration) lasting up to 600 ms. 2. Agonist (AG1) and antagonist (ANT1) bursts were associated with acceleration. AG1 began before acceleration onset. ANT1 started after the onset of AG1 and was often partially coextensive with AG1. The initial phasic activity was followed by tonic EMG activity during the constant-velocity phase of the movements. Movement deceleration was associated with an antagonist burst (ANT2) and an agonist (AG2) burst. 3. Subjects could alter the magnitudes of the acceleration- and deceleration-related activities independently, with resulting independent changes in the movement acceleration and deceleration. 4. When the duration of the constant-velocity phase was decreased, the agonist/antagonist burst pairs occurred progressively closer in time. When movement duration was decreased to the point at which the velocity profile resembled that of step-tracking movements, the four periods of phasic EMG activity formed the classic triphasic pattern. 5. Triphasic EMG patterns were occasionally seen at the beginning or end of long-duration, constant-velocity movements. When they occurred, these triphasic patterns were associated with an acceleration/deceleration pattern similar to that seen in step-tracking movements. 6. The data indicate that paired agonist/antagonist activation is the basic unit of movement control. The AG1/ANT1 burst pair determines the increase and decrease of acceleration, respectively, and the ANT2/AG2 burst pair the increase and decrease of deceleration. These muscle activation pairs can be combined as needed to produce movements having different temporal characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗
PubMed1987

Velocity curves of human arm and speech movements.

The velocity curves of human arm and speech movements were examined as a function of amplitude and rate in both continuous and discrete movement tasks. Evidence for invariance under scalar transformation was assessed and a quantitative measure of the form of the curve was used to provide information on the implicit cost function in the production of voluntary movement. Arm, tongue and jaw movements were studied separately. The velocity curves of tongue and jaw movement were found to differ in form as a function of movement duration but were similar for movements of different amplitude. In contrast, the velocity curves for elbow movements were similar in form over differences in both amplitude and duration. Thus, the curves of arm movement, but not those of tongue or jaw movement, were geometrically equivalent in form. Measurements of the ratio of maximum to average velocity in arm movement were compared with the theoretical values calculated for a number of criterion functions. For continuous movements, the data corresponded best to values computed for the minimum energy criterion; for discrete movement, values were in the range of those predicted for the minimum jerk and best stiffness criteria. The source of a rate dependent asymmetry in the form of the velocity curve of speech movements was assessed in a control study in which subjects produced simple raising and lowering movements of the jaw without talking. The velocity curves of the non-speech control gesture were similar in form to those of jaw movement in speech. These data, in combination with similar findings for human jaw movement in mastication, suggest that the asymmetry is not a direct consequence of the requirements of the task. The biomechanics and neural control of the orofacial system may be possible sources of this effect.

Arm↗
PubMed1986

Initial agonist burst is modified by perturbations preceding movement.

Experiments were conducted to investigate the role of peripheral feedback in modulating the initial agonist burst. Subjects performed visually guided step-tracking movements about the elbow. Brief (50 ms) torque pulse perturbations were randomly applied immediately prior to movement and either opposed (load) or assisted (unload) the forthcoming movement. Load perturbations caused both components of the initial agonist burst to increase in magnitude. In contrast, unloading increased the magnitude of the first component but decreased the second component. These effects were graded with the size of the perturbation, with large perturbations causing a greater change in component magnitude than small perturbations. These results support recent evidence that the initial agonist burst is comprised of individual subunits of activity which can be independently modulated by the central nervous system prior to movement.

Electromyography↗
PubMed1986

Phase plane tracking: a new method for shaping movements.

Study of the relation between muscular activation patterns and movements has largely been based on the control of discrete movement parameters as amplitude, duration and maximum velocity. A new method is described for shaping voluntary limb movements in order to reliably obtain movements of different dynamic characteristics. A template of the desired movement is calculated with a micro-computer. This template is displayed on a storage oscilloscope as a phase plane (velocity vs. position during movement). By moving an instrumented handle the subject reproduces the template movement. Subjects readily adapt to this display and reliably make movements of different dynamic characteristics.

Humans↗
PubMed1985

Initial agonist burst duration changes with movement amplitude in a deafferented patient.

Changes in the duration of the initial agonist burst were studied in a deafferented human. The patient had been functionally deafferented for five years, having no touch, vibration, pressure or kinesthetic sensation nor any tendon reflexes in the four limbs. Pain and temperature sensation were intact and motor fibres were unaffected. The subject made visually guided step-tracking movements using flexion/extension movements about the elbow. Initial agonist burst duration increased with movement amplitude. Burst duration was approximately 65 ms in small movements (6-12 deg) increasing to 136 ms in intermediate (36 deg) and 200 ms in large (54 and 60 deg) movements. Similar changes in initial burst duration with movement amplitude were seen when the subject made non-visually guided movements. It is concluded that the duration of the initial agonist burst is centrally determined.

Adult↗
PubMed1984

Initial agonist burst duration depends on movement amplitude.

The initial burst of EMG activity associated with arm movements made by normal human subjects was studied. Subjects made visually guided, steptracking movements of different amplitudes and speeds. The duration of the initial agonist burst was greater for large than for small amplitude movements. The burst duration was not continuously graded but was either short (70 ms) for small amplitude movements (less than 20 deg) or long (140 ms) for large amplitude ones (greater than 50 deg). Movements of intermediate amplitudes (30-40 deg) were made with both short and long duration bursts. The increase in the duration of the initial agonist burst for large movements was produced by the appearance of a second component in the burst. Both components were of the same duration and occurred before movement peak velocity was reached. Intramuscular recording showed that both components originate from the same muscle. Similar observations were made in both fast and slow movements and in both the biceps and triceps muscles when they were being used as agonists. The data show that the central nervous system has two mechanisms for generation of large amplitude movements: modulation of the magnitude of the initial agonist burst and generation of a second component or pulse of agonist activity at the start of movement.

Arm↗