Primate motor cortex and free arm movements to visual targets in three-dimensional space. I. Relations between single cell discharge and direction of movement.
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We describe the relations between the neuronal activity in primate motor cortex and the direction of arm movement in three-dimensional (3-D) space. The electrical signs of discharge of 568 cells were recorded while monkeys made movements of equal amplitude from the same starting position to 8 visual targets in a reaction time task. The layout of the targets in 3-D space was such that the direction of the movement ranged over the whole 3-D directional continuum in approximately equal angular intervals. We found that the discharge rate of 475/568 (83.6%) cells varied in an orderly fashion with the direction of movement: discharge rate was highest with movements in a certain direction (the cell's "preferred direction") and decreased progressively with movements in other directions, as a function of the cosine of the angle formed by the direction of the movement and the cell's preferred direction. The preferred directions of different cells were distributed throughout 3-D space. These findings generalize to 3-D space previous results obtained in 2-D space (Georgopoulos et al., 1982) and suggest that the motor cortex is a nodal point in the construction of patterns of output signals specifying the direction of arm movement in extrapersonal space. (+info)
Evaluation of joint mobilization treatment. A method.
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The purpose of this study was to develop and test a method for evaluating the effects of joint mobilization treatment on hypomobile joints. The normal dog carpal joint was used as the experimental model. The right carpal joints of 12 dogs were immobilized for six weeks resulting in joint hypomobility. The study group was divided into Treatment (n = 6) and Control (n = 6) Groups. In each group, passive range of motion (PROM) and the following functions during gait were evaluated cinematographically before immobilization and once weekly for four weeks after immobilization: peak extension and peak flexion of the carpal joint and the amount of time required in the gait cycle to reach these peak points. Additionally, the Treatment Group was given mobilization therapy daily during the four weeks after immobilization. The model proved to be satisfactory for evaluating the effect of mobilization treatment on hypomobile joints with the Treatment Group showing improved PROM and motion during gait. The success of the method should direct further investigation of the effects of mobilization treatment on restoration of joint function. (+info)
Neuronal activity in cortical efferent zones projecting to wrist extensors during voluntary wrist extension in the monkey.
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Three monkeys were trained to make rapid wrist extension on presentation of a cue light. After training the animal sufficiently, unit activity was recorded from the cortical efferent zones corresponding to the wrist extensors. Most neurons in the wrist extensor zone were increased in their discharge rate during the wrist extension. Their activation pattern, especially the onset time, varied among different neurons. The earliest neuron was activated 65 msec before the EMG onset of the wrist extensors, while the latest did 30 msec after the EMG onset. About 80% of them activated before the EMG onset. In contrast, variation of the discharge onset of each neuron was rather small and 5-15 msec in quartile deviation. These findings may suggest that each neuron in the cortical efferent zone functions in different timing in the voluntary phasic contraction of the target muscle. (+info)
A model for ulnar dysmelia.
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The treatment of pregnant rats with the carbonic anhydrase inhibitor, acetazolamide, produced gross limb malformations primarily affecting the forepaw, but also producing variable ulnar dysmelia. Analysis of the cytoarchitecture of the ulnar dysmelic limbs showed the presence of cartilaginous and fibrocartilaginous connections between the ulnar and radial chondroepiphyses, with variable deformation of the radial chondroepiphysis by the tethering effect (although the growth plate, per se, did not appear affected at the stage of development studied). The extremely variable experimental appearances duplicated most of the variations seen in the human disease analogue, and suggest this drug-induced embryopathy may be useful as a model for the study of postaxial forelimb deformities in the postnatal phase in order to adequately assess the structural changes of disparate growth between radius and ulna due to the presence of the cellular continuity between the two distal chondroepiphyses. (+info)
Observations on chronic polyarthritis in monkeys.
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Erosion and inflammatory changes in the carpus, fingers and toes of a rhesus monkey, Macaca mulatta, are described; this was one of 152 animals in each of which four fixed limbs were available for examination. The histological changes resembled closely those found in adult human rheumatoid arthritis. The limited literature is reviewed (including cases with amyloid disease). (+info)
Muscular production of individuated finger movements: the roles of extrinsic finger muscles.
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Individuated finger movements--those in which one or more fingers are moved relatively independently of the movement or posture of other body parts--are produced in part by the action of the extrinsic finger muscles. Flexion/extension movements of the fingers are particularly dependent on these extrinsic muscles, most of which are multitendoned. How can contraction of multitendoned muscles move one digit without producing equivalent motion in other digits? This question was addressed by recording EMG activity from muscles of the forearm as trained rhesus monkeys performed flexion and extension individuated movements of each digit of the hand and of the wrist. Recordings showed that during movements of different fingers, a given muscle could act as an agonist, antagonist, or stabilizer of the digits it serves. Furthermore, during a given finger movement, several different muscles typically were active. A three-level connection model was developed that computed the relative motion of the digits during each finger movement based on the changes in EMG activity in the recorded muscles. The model showed that EMG activity changes in the extrinsic finger muscles, and the thenar muscles, could account for most of the motion of both the instructed digit and noninstructed digits. These results indicate that individuated finger movements were produced not by independent sets of muscles acting on each digit, but by the activity of several muscles, many of which act on more than one digit, combined such that the net effect was movement of one digit more than others. (+info)
The mechanical properties of equine third metacarpals as affected by age.
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Twenty-five pairs of equine third metacarpals (McIII) were collected from horses of varying breeds and ranging in age from 1 d to 27 yr. Standard three-point bending tests were performed on the McIII to obtain comparative data on breaking load (BL), breaking strength (BS), and elasticity (E). Broken bones were reassembled and 2-cm sections cut from the bone 1 cm below the nutrient foramen and at the site of the break. Bone mineral content (BMC) and geometrical properties of these sections were determined. Maximum BMC (17.3 g/2 cm) was reached at 6.0 +/- 1.8 yr of age. Horses in this study achieved 76% of maximum BMC by 1 yr of age. Maximum BL (1,888 kg) was reached at 4.6 +/- 1.8 yr of age. The coefficient of determination (r2) between BMC and BL was .92 (P < .001). Breaking strength peaked at 2,272 kg/cm2 at 6.3 +/- 1.2 yr of age. The correlation between BS and BMC was .84 (P < .0001). At 1 yr of age BS was 1,919 kg/cm2, or 85% of maximum BS. Elasticity increased linearly with log 10 age (r2 = .91). The r2 of BMC and E was .79 (P < .001). Area moment of inertia (I) of the cortex of the bone was best approximated by the area of an ellipse (r2 = .91; P < .01). Results suggest that bone strength in horses peaks after most race horses have completed their careers. (+info)
Step-tracking movements of the wrist. III. Influence of changes in load on patterns of muscle activity.
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Human subjects performed step-tracking movements of the wrist in the radial direction. Movement amplitude, external load, and accuracy instructions were varied. We used surface electrodes to record muscle activity from an agonist, extensor carpi radialis longus, and an antagonist, extensor carpi ulnaris. When subjects performed movements "as fast as possible" that were opposed by different external loads, we observed two distinct patterns of modulation of the agonist burst. In one pattern, termed pulse-height modulation, the force of the agonist muscle was graded by varying the peak amplitude of a short-duration agonist burst. This pattern occurred when subjects performed movements of different amplitudes with a lightweight manipulandum. In the other pattern, termed pulse-width modulation, the force of the agonist muscle was graded by varying the duration of an agonist burst of nearly maximal amplitude. When the agonist burst was prolonged, the onset of antagonist activity was delayed. This pattern occurred when subjects performed movements of different amplitudes that were opposed by elastic or viscoelastic loads applied to a heavy manipulandum. The strongest subject exhibited more pulse-height modulation and less pulse-width modulation of the agonist burst than other subjects. Conversely, the weakest subject displayed more pulse-width modulation of the agonist burst than other subjects. These observations indicate that the force requirements of a task, relative to the force generating capacity of a subject's agonist muscle(s), have a significant influence on the pattern of agonist modulation. In a second experiment using three nonhuman primates, we observed that agonist bursts in wrist flexor and extensor muscles exhibited strikingly different patterns of modulation. For wrist flexion, agonist bursts in wrist flexors were brief and displayed pulse-height modulation when movement amplitude was varied. For wrist extension, agonist bursts in wrist extensors were prolonged and displayed largely pulse-width modulation when movement amplitude was varied. We suggest that the distinct patterns of modulation observed in the wrist muscles of monkeys were due to differences in the strength of wrist flexors and extensors, rather than to alterations in movement strategy. In a third experiment, we instructed human subjects to be "accurate" when they made step-tracking movements. When subjects performed movements with a lightweight manipulandum, most displayed short-duration agonist bursts that were pulse-height modulated. When subjects performed "accurate" movements that were opposed by elastic loads, they displayed pulse-width modulation of a small-amplitude agonist burst.(ABSTRACT TRUNCATED AT 400 WORDS) (+info)