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At least 649 records · Page 36Linked to original sources
PubMed2000

Relations between the directions of vibration-induced kinesthetic illusions and the pattern of activation of antagonist muscles.

In humans, tendon vibration evokes illusory sensations of movement that are usually associated with an excitatory tonic response in muscles antagonistic to those vibrated (antagonist vibratory response, AVR), i.e., in the muscle groups normally contracted if the illusory movement had been performed. The aim of the present study was to investigate the relation between the parameters of the illusory sensation of movement and those of the AVR and to determine whether vectorial models could account for the integration of proprioceptive inputs from several muscles, as well as for the organization of the elementary motor commands leading to one unified motor response. For that purpose, we analyzed the relations between the anatomical site of the tendon vibration, the direction of the illusory movement, the muscles in which the AVR develops, and the characteristics of the AVR (surface EMG, motor unit types, firing rates, and activation latencies). This study confirmed the close relationship between the parameters of an AVR and those of the kinesthetic illusion. It showed that, during illusions of movements in different directions, motor units are activated according to a specific pattern correlated with their type, with the direction of the illusory movement and with the biomechanical properties of their bearing muscles. Finally, kinesthetic illusions and AVRs can be effectively represented using similar vectorial computations. These strong relations between the perceptual and motor effects of tendon vibration once again suggest that the AVR may result from a perceptual-to-motor transformation of proprioceptive information, rather than from spinal reflex mechanisms.

Action Potentials↗
PubMed2001

Contribution of vision and cutaneous sensation to the control of centre of mass (COM) during gait termination.

This study employed manipulation of sensory inputs (vision and plantar-surface cutaneous sensation) during gait termination to elicit insight into the roles played by these sensory systems in the control of gait termination. Attenuation of cutaneous sensation was achieved through hypothermic anesthesia. Visual information was occluded using special glasses. The subjects were asked to walk along an 8 m walkway and during randomly selected trials (25% of trials) to terminate their gait in a predetermined area. The centre of mass (COM) was obtained in order to provide an indication of the efficiency and stability during termination when sensory inputs were manipulated. Lack of visual information delayed the initiation of the slowing down of the COM forward progression and increased the step length of the last step of termination. Additionally, lack of vision resulted in the COM moving closer to the base of support (BOS) during double support and more variability, in the COM, when attempting to achieve a final stable position. Insensitivity of the plantar-surface mechanoreceptors led to a longer second step and a more variable foot placement of the first step, and increased the loading rate during the final two steps of termination. Additionally when vision and cutaneous information were absent the resolution of the final stable position was not as effectively controlled. The results demonstrated that visual information about self-motion and object-motion and sensation from the plantar surface of the foot play phase-specific roles in the control of COM during gait termination.

Adult↗
PubMed2003

Rhythmic and discrete elements in multi-joint coordination.

Everyday actions invariably consist of a combination of discrete and rhythmic elements within or across joints. The study investigated constraints arising from the co-occurrence of the two actions in a two-joint task and how endpoint trajectories are shaped due to these action elements at the joint level. The task consisted of an elbow oscillation in the plane that was to be merged with a fast discrete adduction or abduction in the shoulder triggered by an auditory signal. The task was performed with and without explicit instruction about the joint involvement. Two hypotheses were tested: (1) kinematic constraints for the coupling of discrete and rhythmic elements arise at the neuro-muscular level, such that EMG bursts of the discrete and rhythmic movement have a tendency to synchronize. This effect was documented previously in a comparable single-joint task. (2) The merging of the two elements is constrained by intersegmental torques such that initiation and performance of the discrete movement utilizes interaction torques. This hypothesis rests on the assumption that the CNS has an internal model of the limb dynamics and exploits passive torques. Key results support hypothesis 1: (i) the discrete action's initiation at the shoulder was constrained to a preferred phase of the ongoing elbow oscillation. (ii) The rhythmic elbow movement showed a systematic phase advance during the discrete shoulder shift, similar to those reported for the single-joint variant of the task. Reaction times of the discrete movement were longer and peak velocities slower than reported for isolated discrete movements, due to the simultaneous presence of the oscillation. (iii) Interaction torques acting from the elbow onto the shoulder joint were not selectively exploited for the acceleration of the discrete shoulder movement. Indirectly however, hypothesis 2 also found support: torques at the elbow generated compensatory muscle activity in the shoulder that stabilized the stationary joint. It was this rhythmic activity that posed the direct constraints on the initiation of the discrete movement.

Adult↗
PubMed1999

The kinesthetic threat eyeblink: a new type of anticipatory eyeblink response.

The present paper is part of a systematic exploration of naturally acquired conditioned eyeblink responses in human subjects. Normal human subjects were examined for the presence of anticipatory eyeblinks in a new paradigm. They were instructed to move their hand quickly toward their face and tap their forehead. In this situation, subjects generated anticipatory eyeblinks which were initiated before the forehead tap. Additional experiments revealed that visual stimuli and internal movement-planning cues are not required for the initiation of this response. The kinesthetic information from the passively moving arm, however, was sufficient to trigger this kinesthetic threat eyeblink response (KTER). The KTER extinguished when the forehead tap did not reinforce it. These data indicate that the KTER is a unique type of naturally acquired conditioned response system which is maintained by aversive reinforcing events.

Acoustic Stimulation↗
PubMed2002

Tool-use changes multimodal spatial interactions between vision and touch in normal humans.

In a visual-tactile interference paradigm, subjects judged whether tactile vibrations arose on a finger or thumb (upper vs. lower locations), while ignoring distant visual distractor lights that also appeared in upper or lower locations. Incongruent visual distractors (e.g. a lower light combined with upper touch) disrupt such tactile judgements, particularly when appearing near the tactile stimulus (e.g. on the same side of space as the stimulated hand). Here we show that actively wielding tools can change this pattern of crossmodal interference. When such tools were held in crossed positions (connecting the left hand to the right visual field, and vice-versa), the spatial constraints on crossmodal interference reversed, so that visual distractors in the other visual field now disrupted tactile judgements most for a particular hand. This phenomenon depended on active tool-use, developing with increased experience in using the tool. We relate these results to recent physiological and neuropsychological findings.

Adult↗
PubMed2002

Sense of body and sense of action both contribute to self-recognition.

Recognizing oneself, easy as it appears to be, seems at least to require awareness of one's body and one's actions. To investigate the contribution of these factors to self-recognition, we presented normal subjects with an image of both their own and the experimenter's hand. The hands could make the same, a different or no movement and could be displayed in various orientations. Subjects had to tell whether the indicated hand was theirs or not. The results showed that a congruence between visual signals and signals indicating the position of the body is one component on which self-recognition is based. Recognition of one's actions is another component. Subjects had most difficulty in recognizing their hand when movements were absent. When the two hands made different movements, subjects relied exclusively on the movement cue and recognition was almost perfect. Our findings are in line with pathological alterations in the sense of body and the sense of action.

Adult↗
PubMed2003

Spatial updating of environments described in texts.

People update egocentric spatial relations in an effortless and on-line manner when they move in the environment, but not when they only imagine themselves moving. In contrast to previous studies, the present experiments examined egocentric updating with spatial scenes that were encoded linguistically instead of perceived directly. Experiment 1 demonstrated that, regardless of the mode of rotation (physical or imagined), egocentric updating takes place in a deliberate and backward fashion when the locations of objects are anchored in a mental framework. Experiment 2 involved only imagined rotations and showed that results remained unchanged when spatial labels were removed from the scene descriptions. Experiment 3 provided evidence that physical rotations--but not imagined rotations--lead to on-line updating of egocentric relations, provided that the objects of the scene are represented in a sensorimotor framework. The present results suggest that physical movements and sensorimotor encoding are both prerequisites of effortless egocentric updating.

Adolescent↗
PubMed2002

Far bias on the radial line bisection task: measuring perceptual-attentional and motor-intentional bias in normal subjects.

Normal subjects usually err distally when bisecting radial lines below eye level in midsagittal space (far bias). To learn if a radial line bisection bias may be characterized as primarily perceptual-attentional or primarily motor-intentional, we had subjects bisect lines while watching their hand and the line under two video monitoring conditions. In the DIRECT condition, proximal (near) and distal (far) on the video monitor corresponded with the workspace where subjects bisected lines. In the INDIRECT condition, we reversed proximal and distal as they appeared on the monitor. Thus, in the indirect condition, distal hand movement appeared proximal, and vice versa. In the DIRECT condition, subjects erred toward far space (mean 2.075 mm). In the INDIRECT condition, however, subjects erred proximally (mean 1.59 mm, near bias). Distal-proximal reversal of errors over the group of subjects is consistent with a primarily perceptual-attentional bias. In lower body space, normal visual-perceptual-attentional systems may be more biased toward far space than are kinesthetic-motor systems.

Adolescent↗
PubMed1995

The influence of target perturbation on manual aiming asymmetries in right-handers.

Ten right-handed subjects performed 100 target-aiming movements with each hand. These movements were directed toward a small target on the midline. On 60% of the trials, the target remained stationary. On other randomly placed trials, the target "jumped" to a location 3 cm to the right (20%) or left (20%) of its original position when the cursor had travelled 6.5 cm. Although no hand differences were evident in the control condition, the right hand acquired the new target location more quickly than the left hand when the target was perturbed in either direction. Kinematic data revealed that this advantage was not due to initiating an adjustment to the initial movement more rapidly, but rather less time decelerating the corrective movement. Movement adjustments on perturbed trials were implemented more rapidly in left space than right space independent of the hand doing the aiming. These asymmetries may reflect the differential role of the two cerebral hemispheres in the control of goal-directed movements.

Female↗
PubMed1994

Spatial bias in visually-guided reaching and bisection following right cerebral stroke.

Groups of patients with left or right unilateral cerebral stroke were tested for their ability to reach either toward a single visual target or midway between 2 targets. The tasks were performed both in free vision and in conditions preventing visual feedback from the hand. It was found that only the right CVA patients were inaccurate in reaching, and only when visual feedback was absent. This effect of right hemisphere lesions took the form of a rightward bias, present throughout the trajectory of the hand during the reach. It was present regardless of the hand used in reaching and whichever of the two tasks was performed, and was of a similar magnitude irrespective of target location. It is suggested that this rightward bias might reflect the 'premotor' effects that have been proposed to contribute to line-bisection errors in certain patients with visuospatial neglect.

Aged↗
PubMed1993

A differential effect of concurrent verbal activity on right arm movements rightwards and leftwards.

Twenty right-handed male subjects had to follow a target which moved horizontally with a velocity of 40 degrees/s either rightwards or leftwards by moving their right arm. During the pursuit movement, subjects had to speak a sentence or to accomplish this procedure without speaking. It could be shown that while subjects spoke, the pursuit movement was performed more inaccurately than during the control session. Furthermore, it was shown that during concurrent speaking, pursuit movements rightwards were more inaccurate than movements to the left. This result is in line with theoretical implications according to which visually guided right-arm movements rightwards are controlled by a neural network located in the left hemisphere, whereas right-arm movements leftwards are controlled by a neural network distributed over both hemispheres.

Adult↗
PubMed1978

Handedness effects in kinesthetic spatial location judgements.

This experiment examines hemispheric assymetry in reproduction of spatial location in the kinesthetic modality. Using a dichotomous presentation technique, blindfolded, right-handed subjects moved both arms (arm positioning task) or the thumb (thumb positioning task) of each hand simultaneously to predetermined spatial locations and were subsequently asked to reproduce these locations. The results showed a marked left hand advantage only in the thumb positioning task suggesting that the right hemisphere was superior in performing this task. These data were discussed as they relate to other evidence pertaining to cerebral hemispheric specialization in motor activities.

Dominance, Cerebral↗
PubMed1983

Elaboration of representations in a left-handed subject with callosal damage.

Four experiments were carried out in a familial left-handed patient who, following a vascular accident, underwent a callosal lesion and had a right hemianopia. Previous observations by Poncet et al. (1978) demonstrated that both hemispheres controlled expressive language. In the first experiment haptic unimanual exploration showed that each system (right hand/left hemisphere; left hand/right hemisphere) elaborated very different mental representations of the stimulus and gave different types of verbal report of it (naming and talking about). In the second experiment, manual exploration of a maze in the search of a target was performed randomly with the right hand and following a competent spatial strategy with the left hand. The third experiment investigated the ability of the right hemisphere to discriminate the phonetic features of the names of objects that were identified but not named. In the fourth experiment, recognition memory of objects was shown to be better when information was processed by the left hand - right hemisphere system than by the right hand - left hemisphere system. Findings are discussed in terms of verbal vs. non-verbal processes and of perceptual awareness.

Adolescent↗
PubMed1984

Spatial location judgements by right and left-handers.

An attempt was made to replicate the left-hand advantage found by Roy and Mackenzie (1978) for a bimanual thumb-positioning task. As in their experiment strongly right-handed male and female subjects took part, and in addition strongly left-handed male and female subjects took part. Their findings were not fully replicated. A weak left-hand advantage was found for only one of the three error measures used (constant error). Significant interactions of sex with handedness were found for absolute and constant error. The difficulty of replication and current findings are discussed in terms of possible variations in subject strategy which warrant further investigation.

Adult↗
PubMed1987

Lateralization of kinesthetically guided spatial perception.

The present study measured unimanual kinesthetic discrimination for the right and left thumb angular position of male and female right handers without left handed relatives. Each subject's discrimination threshold and constant error were obtained by the Method of Constant Stimuli. Subjects either made an active movement in assessing the standard thumb angle or were passive while the angle was set by the experimenter. Subjects either reported their decision orally or made a non-verbal movement. A difference was found between the thumbs in the direction of more sensitive kinesthetic discrimination by the left thumb (right hemisphere). The left thumb was found to have smaller discrimination threshold of angular position by about 20% over the right thumb. Sex, passive movement mode, and verbal response were not related to the lateralization effect.

Adult↗
PubMed1987

Pedal asymmetry in the reproduction of spatial locations.

Roy and MacKenzie (1978) showed that the left thumb is superior to the right thumb in reproducing a spatial location. This study replicated and extended their findings to the reproduction of spatial locations by the feet. We attribute the left foot advantage in this study to the superiority of the right hemisphere in processing spatial information.

Adult↗
PubMed1975

Acrylic cement stabilized joint replacements.

Surgical management of osteoarthritis, aseptic necrosis and rheumatoid arthritis has been revolutionized by the introduction of acrylic cement-stabilized joint surface replacement. Although single joint surface replacements have been employed extensively for more than half a century, total surface replacement operations with a wear-resistant high-density polyethylene and noncorrosive stainless steel stabilized by acrylic cement were introduced only a little more than 12 years ago. This evolved with Charnley's discovery of the high level of bone tolerance for acrylic cement. Acrylic cement made it possible mechanically to bond artificial joint surfaces to the bone ends and produce an insensitive Charcot-like functioning joint. A barium sulfate additive makes the cement radiopaque for visualizing the bone-cement interface. Barium sulfate additive also lowers the polymerization temperature and opens the polymer for influx of interstitial fluids. Antibiotics have also been added to the cement for prevention and treatment of infection of the surrounding tissues. In aged individuals with cardiovascular disease, the absorption of the acrylic monomer depresses cardiac output and produces hypotension for 2-5 minutes after impaction of acrylic cement into spongy bone. The hypotension has been minimized by cautious fluid replacement and maintenance of adequate blood volume before, during and after the operation. Approximately 30,000 total hip arthroplasties are performed in the United States annually in patients older than 50 years of age with fractured femoral head replacements, bilateral rheumatoid arthritis, old neglected congenital dislocations of the hip or osteonecrosis with and without osteoarthritis. The pain relief is more complete and the functional improvement more predictable than in any other previously recommended surgical operation for the purpose. For this reason, total hip arthroplasty has almost completely supplanted mold-arthroplasty, osteotomy, capsulotomy (hanging hip) and resection of the femoral head. Hemiarthroplasty in the form of femoral head replacement still is the procedure of choice in patients with fractures of the neck of the femur and a normal acetabular articular cartilage, irrespective of age. As a countermeasure against loosening of the prosthesis in patients with osteoporosis and a hollow proximal end of the femur, the stem can be stabilized with acrylic cement. A standard replaceable femoral head for subsequent conversion of femoral head replacement to total hip arthroplasty is an important consideration and presently is under investigation in several medical centers.(ABSTRACT TRUNCATED AT 400 WORDS)

Acrylates↗