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Biomedical subjects

R W Angel

Publications and source records attributed to R W Angel.

At least 19 recordsLinked to original sources
PubMed1988

Axial versus distal motor impairment in Parkinson's disease.

We measured axial (head rotation) and distal (wrist flexion and extension) movements in parkinsonian patients with varying stages of disability, before and after administration of L-dopa. Velocities for both movements were proportionately reduced in all stages of disease. L-Dopa administration provided a small but consistent increase in distal movement velocity for most patients, whereas in patients with advanced disease (stages III to V), axial movement velocity actually declined after administration of L-dopa. This decline may be partially responsible for the failure of L-dopa administration to reverse the loss of "righting reflexes" in these patients. Measurement of axial motor control may be a useful tool in evaluating therapeutics for Parkinson's disease patients.

Aged↗
PubMed1987

Unloading reflex of a hand muscle.

The unloading reflex of abductor hallucis brevis was elicited by removal of the external load during voluntary contraction. The duration of the unloading pulse was varied experimentally from 1 to 32 msec. With all stimulus durations, the response was a measurable decrease in the level of EMG activity. Expressed as a percentage change from baseline, the mean size of the unloading reflex was a logarithmic function of the unloading pulse duration. The results demonstrate that the hand muscles are sensitive to very brief mechanical stimuli. Although the motoneurons of the intrinsic hand muscles receive strong projections from the cerebral cortex, they exhibit reflex behavior similar to that of the large, postural muscles.

Adult↗
PubMed1986

Recovery of somatosensory evoked potential amplitude after movement.

Sensory transmission is known to be impaired during movement of the stimulated body part. The goal of this study was to determine whether sensory gating persists for a measurable time after completion of a voluntary movement. Tactile stimuli were applied to the right index fingertip at intervals ranging from 63 to 1,000 msec after the completion of rapid thumb movement. Somatosensory evoked potentials (SEPs), recorded over the left cerebral hemisphere, were found to be reduced in size for at least 500 msec after the cessation of movement. The prolonged attenuation of SEPs after movement appears to depend on a central process that persists for a measurable time after the movement has ended.

Adolescent↗
PubMed1986

Central error-correcting behavior in schizophrenia and depression.

A previous study suggested that schizophrenic subjects exhibit an impaired ability to correct their own errors of movement without using exteroceptive signals. However, the performance of schizophrenic subjects was compared to that of only one other psychiatric group (alcoholic subjects), and a relatively small number of subjects was studied. To investigate the specificity of the postulated impairment, 9 schizophrenic, 11 depressed, and 8 normal subjects performed a tracking task designed to prevent the use of exteroceptive cues in correcting errors of movement. The depressed and normal groups did not differ significantly on any performance measure, but the schizophrenic subjects again demonstrated a gross impairment in correcting errors, yet no impairment in initiating correct responses. These findings suggest that the impaired ability to monitor ongoing motor behavior on the basis of internal, self-generated cues may be specific to schizophrenia among major psychiatric disorders.

Adult↗
PubMed1986

Stretch and unloading reflexes in a human hand muscle.

Stretch and unloading reflexes were demonstrated in the first dorsal interosseous muscle by averaging the electromyographic responses to brief mechanical stimuli. Subjects were not able to abolish these reflexes by altering their preparatory set. When subjects were prepared to contract or relax the muscle in response to a stretching force, the size of the stretch reflex was not affected significantly. When they were prepared to contract or relax in response to unloading, the "silent period" was diminished. In general, these reflexes were not modulated appropriately to improve the performance of an intended voluntary movement. Our results do not support the notion that spinal reflexes of the intrinsic hand muscles are "dominated" by corticospinal inputs.

Adult↗
PubMed1985

Decrement of somatosensory evoked potentials during repetitive stimulation.

In normal subjects, cerebral potentials were evoked by brief, passive extension of the wrist joint at various interstimulus intervals (ISIs). The resulting somatosensory evoked potentials (SEPs) were found to decrease during repetitive stimulation. The greatest decrement occurred between the first and second responses of each series. After cessation of stimuli, the SEP amplitude returned to control values over a prolonged, exponential time course. The authors postulate that the observed response decrement may be a form of habituation, which provides a model for studying the neuronal substrates of behavior.

Adult↗
PubMed1985

Gating of somatosensory perception following movement.

Tactile stimuli were applied to the right index finger at selected times following rapid movements of the thumb. The probability of detecting a stimulus was found to be impaired for at least 250 ms after completion of a voluntary movement. This finding complements previous work showing that somatosensory evoked potentials are reduced for a comparable period following movement.

Adolescent↗
PubMed1985

Velocity-dependent suppression of somatosensory evoked potentials during movement.

Sensory transmission is known to be impaired during movement of the stimulated body part. This phenomenon is manifested by a decrease of perceptual acuity and a correlated decrease in the size of somatosensory evoked potentials (SEPs). The goal of the present study was to define the relationship between SEP amplitude and speed of movement. SEPs were elicited by brief (25 msec) loading of the wrist flexor muscles. Stimuli were applied while the wrist joint was stationary or moving voluntarily at one of several velocities. In all subjects, SEP amplitude was approximately inversely related to speed of movement at the time of stimulation. The findings refine and extend studies suggesting the velocity dependence of sensory suppression during movement.

Adult↗
PubMed1982

Impaired central error-correcting behavior in schizophrenia.

Previous work has suggested that normal subjects are able to recognize and correct their own errors of movement without using exteroceptive signals. This ability may be impaired in schizophrenia. Twelve normal subjects, 12 alcoholics, and 14 schizophrenics performed a step-function tracking task designed to prevent the use of exteroceptive signals in correcting errors of movement. The mean probability of correcting an error without external cues was approximately .38 in schizophrenics, .70 in normal subjects, and .75 in hospitalized alcoholic patients. There was no difference between groups in the ability to initiate correct responses. The results suggest that schizophrenics are deficient in the ability to monitor ongoing motor behavior on the basis of internal, self-generated cues.

Adult↗
PubMed1978

Unloading and shortening reactions in Parkinson's disease.

The unloading reflex was tested on both sides of a patient with asymmetrical Parkinsonism. The motor activity after the silent period was significantly greater on the more affected side. The findings support the hypothesis that the response to unloading and the shortening reaction share a common mechanism which is exaggerated in Parkinsonism.

Action Potentials↗
PubMed1977

The rebound phenomenon of Gordon Holmes.

Contrary to a prevalent belief, the rebound phenomenon of Gordon Holmes is not a sign of cerebellar disease. It is elicited by having the patient attempt to move a limb against resistance. When the resistance is suddenly removed, the limb normally moves a short distance in the desired direction and then rebounds (jerks back in the opposite direction). Gordon Holmes pointed out that the rebound phenomenon is (1) present in normal libs, (2) exaggreated in spastic limbs, and (3) absent in limbs affected by cerebellar disease. An awareness of Holmes's observations may be helpful in the diagnosis of both cerebellar disease and spasticity.

Animals↗
PubMed1977

Antagonist muscle activity during rapid arm movements: central versus proprioceptive influences.

Seven normal subjects were instructed to adduct the arm as fast as possible. On some trials the movement was prevented mechanically. For each movement or attempted movement, the EMG response in the antagonist muscle was measured. On trials in which no movement occurred, the respones were significantly smaller than those obtained during free, ballistic movement. The results demonstrate the role of proprioceptive influences on the contraction of the antagonist muscle.

Adult↗
PubMed1977

Understanding and diagnosing senile dementia.

Dementia is one of the most common syndromes afflicting the aged, and it should be ranked as a major cause of death. Senile dementia and Alzheimer's disease should now be viewed as one and the same. Familiarity with the cardinal signs of dementia enables the physician to differentiate it from various "functional" disorders. Before making a diagnosis of senile dementia, it is important to exclude all forms of treatable disease, including toxic, metabolic, infectious, neoplastic, and traumatic disorders. Most older patients with dementia will be found to have Alzheimer's disease, for which no definitive treatment is available.

Aged↗
PubMed1976

Efference copy in the control of movement.

On a two-choice tracking test of normal subjects, numerous false moves were induced when the directional relation between movement of the hand and the response marker was changed. The mean error-correction times were not consistently less than simple reaction times. When the center of the display was screened to eliminate visual feedback, numerous moves were reversed before the marker was visible. The probability of reversing an error was much greater than that of reversing a correct move. The findings are best explained in terms of a central mechanism that uses efference copy to amend errors of movement.

Adult↗