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Biomedical subjects

J D Cooke

Publications and source records attributed to J D Cooke.

At least 19 recordsLinked to original sources
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↗
PubMed1983

Vibration-induced changes in movement-related EMG activity in humans.

The effect of muscle tendon vibration during voluntary arm movement was studied in normal humans. Subjects made alternating step flexion and extension movements about the elbow. A small vibrator was mounted over either the biceps or the triceps muscle and vibration was applied during flexion or extension movements. The vibrator was turned off between movements. After a period of practice, subjects learned the required movements and were able to make them with their eyes closed. Application of vibration to the muscle antagonist to the movement being performed produced an undershoot of the required end-movement position. The undershoot was 20-30% of the total movement amplitude. In contrast, vibration of the muscle agonist to the movement resulted in no change in movement end position. The vibration-induced undershoot was associated with an increase in the EMG activity of the vibrated (antagonist) muscle and a resultant increase in the ratio of the antagonist to agonist EMG activity. The increase in antagonist EMG produced by the vibration occurred with a latency of approximately 60 ms from vibration onset. The observed results are consistent with vibration-induced activation of muscle spindle receptors in the lengthening muscle during movement. It is suggested that, during movement, the sensitivity of the spindle receptors in the shortening muscle is decreased and the information concerning limb position during movement comes primarily from the lengthening muscle.

Electromyography↗
PubMed1983

The effects of cutaneous mechanoreceptor stimulation on the stretch reflex.

The effects of cutaneous stimulation on tonic and phasic responses to stretch were studied in the triceps surae complex of unanesthetized, decerebrate cats. The tonic response was produced by a maintained stretch of the muscle group to 80-85% of its maximum length. Stretch was applied directly to the isolated tendon at the calcaneus. Phasic responses were elicited by a ramp stretch of 1.0 to 2.0 mm superimposed on the maintained stretch. Mild, brief, electrical or mechanical stimulation of the plantar cushion caused a sequence of inhibitory and excitatory changes in the tonic EMG activity in the soleus muscle. Mild stimuli, applied 0.01 to 5 ms before the start of ramp stretch, decreased the size of the phasic response to stretch and converted it into a biphasic response. It is suggested that stimulation of cutaneous mechanoreceptors may be responsible for variations in the initial burst of EMG activity seen in the agonist muscle during the response to perturbation or fast voluntary movement in animals and man.

Animals↗
PubMed1981

Responses to force perturbations preceding voluntary human arm movements.

Brief force perturbations were applied 30-120 ms prior to onset of step-tracking forearm movements by normal humans. The perturbations altered the first agonist burst of the movement-related triphasic EMG pattern. Perturbations opposing the movement resulted in an increase in the magnitude of the late part of the first agonist burst, the early part being unchanged. Conversely, in movements which would be assisted by the perturbation, EMG magnitude decreased during the late part of the burst. No reflex EMG responses were elicited during the period following the perturbation and preceding onset of the first agonist burst.

Arm↗
PubMed1981

The effects of muscle vibration on the attainment of intended final position during voluntary human arm movements.

Muscle tendon vibration was applied during voluntary step-tracking arm target-movements performed by normal human subjects. Vibration (freq. = 120 Hz) was applied over either the biceps or triceps tendons. During non-visually guided (eyes closed) trials, vibration of the muscle antagonistic to the movement being performed resulted in an undershoot of the required target. Thus, biceps vibration produced an undershoot of the extension target and triceps vibration an undershoot of the flexion target. The same effect occurred if the vibration was applied continuously over several movements or only during the course of individual movements. In contrast, vibration of the muscle acting as the prime mover had no effect on the correct attainment of the required target. It is suggested that the central nervous system may monitor muscle afferent activity of the lengthening (antagonist) muscle during simple, step movements.

Arm↗
PubMed1981

Amplitude- and instruction-dependent modulation of movement-related electromyogram activity in humans.

1. Studies were made of the electromyogram (EMG) patterns associated with the performance of visually guided, step-tracking arm movements by normal humans. Subjects were instructed to make movement either 'accurately', 'as fast as possible' or 'fast and accurately'. Movements of 16, 32, 48 and 64 deg of arc were made with each instruction. Movements had durations of approximately 250-600 msec. 2. A 'triphasic' pattern of EMG activity was associated with all movements in this study. All bursts in this pattern were more clearly defined in faster movements whether the increased speed of movement was a result of increased movement amplitude or of the instruction-related 'intent' of the subject. 3. The magnitudes of the two agonist EMG bursts showed identical linear dependencies on movement amplitude. The slope of this relation was instruction-dependent, being greatest for 'fast' and least for 'accurate' movements. 4. The duration and time of onset of the initial agonist burst relative to the start of the movement were not dependent on movement amplitude or on instruction. In contrast, the time of onset of the second agonist burst depended on both movement amplitude and instruction, occurring earlier when movements were made faster. 5. The magnitude of the antagonist activity was instruction- but not amplitude-dependent. Duration and onset of this burst varied with both instruction and movement amplitude.

Arm↗
PubMed1978

Increased dependence on visual information for movement control in patients with Parkinson's disease.

Studies were made of visually and non-visually guided movements by patients with Parkinson's disease. The subjects moved a light, horizontal handle using rotation primarily about the elbow. During visually guided trials both handle and target positions were displayed to the subject; during non-visually guided trials only the handle position was displayed. During non-visually guided trials all patients showed a tendency for an overall flexion drift, although there was no change in average movement amplitude. The overall error in position by the end of the non-visually guided trials was greatly in excess of the reported values for passive displacement thresholds in normal subjects. It is suggested that the data indicate an increased dependence on visual information for control of motor activity in Parkinson's patients.

Aged↗
PubMed1977

Long-loop reflexes in the tranquilized monkey.

EMG responses to sudden displacement of the forelimb were studied in Cebus monkeys tranquilized with Atravet, a phenothiazine tranquilizer. The monkey's forearm was strapped firmly to a manipulandum handle. A torque motor attached at the pivot point of the handle, under servo control, provided reproducible limb displacements. In response to a sudden maintained displacement three periods of EMG activation in biceps muscle occurred with peak latencies of approximately 25, 45 and 85 msec. These correspond to the latencies of the M1, M2 and M3 responses in the alert animal. Similar responses were observed in 'naive' animals which had not previously been used in experimentation. All three responses increased in magnitude with increasing background activity and all appeared to be associated with suppression of EMG activity in the antagonist muscle. M1 and M2 responses were position dependent, M1 being greater in extension than in flexion and M2 the opposite. The position-dependence of the M2 response was produced by a depression of activity following the M1. This depression of activity lasted up to 30 msec following M1 and was directly dependent on the M1 magnitude.

Animals↗
PubMed1976

Modulation of the functional stretch reflex by the segmental reflex pathway.

Electromyographic (EMG) reflex responses were examined in the biceps muscle of awake Cebus monkeys trained to resist perturbations of a handle with their forearm. In particular responses at latencies of 15-20 msec (M1) and 40-55 msec (M2), thought to correspond to segmental and suprasegmental reflex pathways respectively, were studied. The experiments demonstrated that the magnitude of the M1 response was large, as compared to M2, only when the muscle was tonically active and small perturbations were applied. For larger perturbations the magnitude of M1 saturated and the M2 response became functionally significant, its magnitude being directly related to the magnitude of the perturbation. By means of delayed reductions in torque, the magnitude of this M2 response was also shown to be very sensitive to changes in facilitatory drive provided by segmental pathways.

Afferent Pathways↗
PubMed1976

Forearm oscillation during cooling of the dentate mucleus in the monkey.

A study was made of oscillations in arm acceleration in monkeys performing a self-paced manual step-tracking task. Power spectral density analyses of segments of arm acceleration data from normal monkeys containing both flexion and extension movements and intermovement holding periods showed three major peaks at 1-1.5 Hz, 3-5 Hz and 5-7 Hz. Cooling of the dentate nucleus produced a marked increase in the relative magnitude of the 3-5 Hz spectral band. The spectral peak in this frequency range was larger than the other two which were also present during cooling. Autocorrelation functions from long segments of data containing flexion and extension movements and intermovement holding periods showed regular periodic variations in both normal and cooled animals. This suggests that the ongoing oscillations were not changed in phase by the occurrence of the self-initiated arm movements.

Animals↗