Biomedical subjects

M Flanders

Publications and source records attributed to M Flanders.

At least 19 recordsLinked to original sources

PubMed2002

Oculocentric frames of reference for limb movement.

We have reviewed evidence that suggests that the target for limb motion is encoded in a retinocentric frame of reference. Errors in pointing that are elicited by an illusion that distorts the perceived motion of a target are strongly correlated with errors in gaze position. The modulations in the direction and speed of ocular smooth pursuit and of the hand show remarkable similarities, even though the inertia of the arm is much larger than that of the eye. We have suggested that ocular motion is constrained so that gaze provides an appropriate target signal for the hand. Finally, ocular and manual tracking deficits in patients with cerebellar ataxia are very similar. These deficits are also consistent with the idea that a gaze signal provides the target for hand motion; in some cases limb ataxia would be a consequence of optic ataxia rather than reflecting a deficit in the control of limb motion per se. These results, as well as neurophysiological data summarized here, have led us to revise a hypothesis we have previously put forth to account for the initial stages of sensorimotor transformations underlying targeted limb motions. In the original hypothesis, target location and initial arm posture were ultimately encoded in a common frame of reference tied to somatosensation, i.e. a body-centered frame of reference, and a desired change in posture was derived from the difference between the two. In our new scheme, a movement vector is derived from the difference between variables encoded in a retinocentric frame of reference. Accordingly, gaze, with its exquisite ability to stabilize a target image even under dynamic conditions, would be used as a reference signal. Consequently, this scheme would facilitate the processing of information under conditions in which the body and the target are moving relative to each other.

Animals↗

PubMed2002

Capturing the frame of reference of shoulder muscle forces.

We have adjusted and validated models of the lines of action of six human shoulder muscles. Compared to other models of the shoulder mechanism (e.g., 9, 11, 17, 24) ours is greatly simplified in that the scapula and its many muscles are largely neglected, and the action of each of six broad muscles is summarized by a single line segment. The close correspondence between measured and predicted moment direction over a wide range of postures suggests that this latter simplification was reasonable. We found that assignment of two via points (one fixed to the origin and one fixed to the insertion) was adequate to represent the measured actions, and our sensitivity analysis highlights the importance of via point placement. Because our model predicts the action of each muscle over a very large range of arm postures, it should be useful for future investigations of the control of muscle forces.

Adult↗

PubMed2001

Humans adapt the initial posture in learning a whole-body kicking movement.

What strategies are used in learning to control new movements? The present investigation sought to understand this process by analyzing the changes in whole-body kinematics that occurred when subjects attempted to learn an unusual kicking movement. Five novices were taught a capoeira kick that involved both the upper and lower body for balance and co-ordination. Subjects performed two sets of 60 consecutive kicks, 24 h apart. Gradual changes in the body movement and the initial posture were found. Four subjects reduced the dynamic counter-twist associated with kick initiation. These subjects also adopted a more forward initial body lean. This gradual change in initial posture appeared to obviate the early counter-twist and to facilitate both the equilibrium and the goal directed components of the kick.

Adult↗

PubMed2001

Vertical rectus muscle transposition and botulinum toxin for complete sixth nerve palsy.

BACKGROUND: Effective surgical treatment of complete unrecovered sixth nerve palsy must include the transfer of abducting power to the temporal aspect of the globe with release of medial rectus contracture nasally. We describe our experience in the treatment of five such patients who underwent full vertical rectus transposition combined with botulinum toxin chemodenervation of the ipsilateral medial rectus muscle. METHODS: The five patients all had primarily unilateral complete unrecovered sixth nerve palsy. They all underwent a complete preoperative and postoperative eye examination and an orthoptic assessment. Excursion into abduction was graded from -8 (globe immobilized in extreme adduction) to -4 (abduction as far as primary position) to 0 (full abduction). Abduction saccades and a forced muscle generation test confirmed the presence of complete unrecovered sixth nerve palsy, and forced duction testing measured the degree of medial rectus contracture. All patients received ipsilateral medial rectus injection of botulinum toxin in the preoperative (8 to 2 months before surgery) and perioperative periods, and underwent complete superior rectus-inferior rectus transposition temporally. RESULTS: The average length of follow-up was 21 (range 6 to 48) months. The average preoperative distance alignment was 52 (range 25 to 80) prism dioptres (PD). Vertical rectus transposition combined with botulinum toxin injection resulted in an average distance alignment change of 66 PD (range 50 PD to 82 PD) of exoshift. The average final deviation was 1 PD of esotropia (range 4 PD of esotropia to 6 PD of exotropia). Average abduction improved from -6 (range -3 to -8) preoperatively to -1.7 (range -1 to -2) postoperatively. Saccades averaged -4 preoperatively and improved to -2 postoperatively. Normal vertical eye movements were preserved in all patients. A total field of single binocular vision was created in all patients, which averaged 55 degrees (range 30 degrees to 75 degrees) in the horizontal meridian. The field of single binocular vision from primary position into abduction averaged 23 degrees (range 18 degrees to 28 degrees). INTERPRETATION: Temporal transposition of the vertical rectus muscles combined with perioperative botulinum toxin injection of the ipsilateral medial rectus muscle is a reliable and effective way of restoring functional binocular vision in patients with complete unrecovered sixth nerve palsy.

Abducens Nerve Diseases↗

PubMed2001

The Duncker illusion and eye-hand coordination.

A moving background alters the perceived direction of target motion (the Duncker illusion). To test whether this illusion also affects pointing movements to remembered/extrapolated target locations, we constructed a display in which a target moved in a straight line and disappeared behind a band of moving random dots. Subjects were required to touch the spot where the target would emerge from the occlusion. The four directions of random-dot motion induced pointing errors that were predictable from the Duncker illusion. Because it has been previously established that saccadic direction is influenced by this illusion, gaze was subsequently recorded in a second series of experiments while subjects performed the pointing task and a similar task with eye-tracking only. In the pointing task, subjects typically saccaded to the lower border of the occlusion zone as soon as the target disappeared and then tried to maintain fixation at that spot. However, it was particularly obvious in the eye-tracking-only condition that horizontally moving random dots generally evoked an appreciable ocular following response, altering the gaze direction. Hand-pointing errors were related to the saccadic gaze error but were more highly correlated with final gaze errors (resulting from the initial saccade and the subsequent ocular following response). The results suggest a model of limb control in which gaze position can provide the target signal for limb movement.

Fixation, Ocular↗

PubMed2000

Minor burn management: an Australian regional perspective.

Minor burns are commonly treated in hospital emergency departments. This study aimed to identify the nursing management of minor burns in hospitals in the Queensland region of Australia. A total of 200 questionnaires were distributed to hospitals with emergency departments in this region. The semi-structured questionnaire enquired about the respondents' initial and ongoing management of minor burns. Fifty completed questionnaires were returned, a response rate of 25%. Most respondents (80%) were registered nurses and the rest enrolled nurses. The respondents' practice was compared with that recommended in the literature. Their practice reflected the variations found in the literature, suggesting that some may not be as effective or efficient as others. The authors conclude that further research is required on the efficacy of products used in minor burn management.

Australia↗

PubMed2000

Coordination of a step with a reach.

Although natural reaching behavior can easily include forward body movement, most laboratory studies of reaching have constrained the body to be stationary. Recently, however, it has been shown that normal subjects exhibit a different pattern of errors when attempting to pinpoint remembered target locations, depending on whether or not the reach includes a step. In the study of Flanders et al., these errors appeared to be due to the strategy of eye/head/hand coordination which normally comes into play when the body is moving toward the target. Since the spatial positioning of the head was found to partially explain the errors in hand placement, the present study examined the movements of patients with bilateral vestibular deficits in order to further analyze the whole-body coordination. Somewhat surprisingly, the patients exhibited the same pattern of head movement and the same errors in hand placement as did the control subjects. Nevertheless, the patients' movements clearly exhibited evidence for an abnormal decomposition of elbow extension and trunk rotation. Furthermore the patients' (spatial) hand paths were significantly more curved than those of control subjects and, only in the patients, paths to remembered targets were significantly more curved than paths to visible targets. Thus for movements to remembered targets, the patients tended to move the hand to the same incorrect spatial positions as control subjects but spatiotemporal aspects of the arm and body movement differed. The results are consistent with the idea that vestibular patients are overly dependent upon visual cues, and support the hypothesis that this stepping and reaching behavior is largely dependent upon a visual reference signal.

Adult↗

PubMed1999

Reaching beyond reach.

The analysis of errors in two-joint reaching movements has provided clues about sensorimotor processing algorithms. The present study extends this focus to situations where the head, trunk, and legs join with the arm to help reach targets placed slightly beyond arm's length. Subjects reached accurately to touch "real targets" or reached to the remembered locations of "virtual targets" (i.e., targets removed at the start of the reach). Subjects made large errors in the virtual-target condition and these errors were analyzed with the aim of revealing the implications for whole-body coordination. Subjects were found to rotate the head less in the virtual-target condition (when compared with accurate movements to real targets). This resulted in a more limited range of head postures, and the final head angles at the end of the movements were geometrically related to the incorrect hand locations, perhaps accounting for some portion of the errors. This suggests that head-eye-hand coordination plays an important role in the organization of these movements and leads to the hypothesis that a representation of current gaze direction may serve as a reference signal for arm motor control.

Adult↗

PubMed1999

Do arm postures vary with the speed of reaching?

Do arm postures vary with the speed of reaching? For reaching movements in one plane, the hand has been observed to follow a similar path regardless of speed. Recent work on the control of more complex reaching movements raises the question of whether a similar "speed invariance" also holds for the additional degrees of freedom. Therefore we examined human arm movements involving initial and final hand locations distributed throughout the three-dimensional (3D) workspace of the arm. Despite this added complexity, arm kinematics (summarized by the spatial orientation of the "plane of the arm" and the 3D curvature of the hand path) changed very little for movements performed over a wide range of speeds. If the total force (dynamic + quasistatic) had been optimized by the control system (e.g., as in a minimization of the change in joint torques or the change in muscular forces), the optimal solution would change with speed; slow movements would reflect the minimal antigravity torques, whereas fast movements would be more strongly influenced by dynamic factors. The speed-invariant postures observed in this study are instead consistent with a hypothesized optimization of only the dynamic forces.

Arm↗

PubMed1999

Fresnel membrane prisms: clinical experience.

BACKGROUND: There are few published reports on the clinical application of Fresnel membrane prisms in the treatment of diplopia in adults. The authors describe the use of these prisms in patients with fourth and sixth cranial nerve palsies, restrictive motility caused by thyroid-related orbital disease, and convergence insufficiency. METHODS: Of 209 patients who had been treated with Fresnel prisms, 141 were selected. The database included patients from a private practice in Montreal, seen from 1988 to 1996, and patients seen by orthoptists in the ophthalmology department of a children's hospital in Montreal between 1992 and 1996. All the patients had diplopia associated with fourth (48 patients) or sixth (43 patients) cranial nerve palsy, thyroid-related orbitopathy (18 patients) or convergence insufficiency (32 patients). After qualitative and quantitative assessment of the ocular misalignment, a Fresnel prism was selected for power and axis and for appropriate location on the spectacle lens. Ocular dominance and side of paresis or restriction were also considered in the placement of the prism. The patient's response to treatment was documented. RESULTS: The Fresnel prisms were oriented horizontally in 72 patients (51%), vertically in 55 (39%) and obliquely in 14 (10%). They were placed on the spectacle lens before the nondominant eye in 127 cases (90%), either covering the entire lens, or on the upper or lower segment or both. The patients were followed for an average of 15 (range 2 to 96) months. Of the 141 patients 113 (80%) had a successful outcome, with relief of their diplopia. Twenty-seven patients (19%) eventually had the prismatic correction ground into the lens, 70 (50%) chose to wear the Fresnel prism on a permanent basis because incorporation into the lens was not possible or because of cost, and 17 (12%) used the Fresnel prism as a temporary device before or after surgery. Most patients who converted to incorporated prisms did so when the prismatic power became stable, usually after 6 to 8 months. Eight patients (6%) stopped using the prism because of associated side effects, such as blurred vision, persistent diplopia, torsion or optical aberrations. INTERPRETATION: The Fresnel prism is an excellent device in treating diplopia in adult patients. It is a reasonable permanent option when incorporating the prism into the spectacle lens is not possible. A fused blurred image caused by a Fresnel prism placed in front of the nondominant eye is preferable to double but clear images.

Abducens Nerve Diseases↗

PubMed1998

Postural hand synergies for tool use.

Subjects were asked to shape the right hand as if to grasp and use a large number of familiar objects. The chosen objects typically are held with a variety of grips, including "precision" and "power" grips. Static hand posture was measured by recording the angular position of 15 joint angles of the fingers and of the thumb. Although subjects adopted distinct hand shapes for the various objects, the joint angles of the digits did not vary independently. Principal components analysis showed that the first two components could account for >80% of the variance, implying a substantial reduction from the 15 degrees of freedom that were recorded. However, even though they were small, higher-order (more than three) principal components did not represent random variability but instead provided additional information about the object. These results suggest that the control of hand posture involves a few postural synergies, regulating the general shape of the hand, coupled with a finer control mechanism providing for small, subtle adjustments. Because the postural synergies did not coincide with grip taxonomies, the results suggest that hand posture may be regulated independently from the control of the contact forces that are used to grasp an object.

Adult↗

PubMed1998

Directional tuning of single motor units.

The directional activity of whole muscles has been shown to be broadly and often multimodally tuned, raising the question of how this tuning is subserved at the level of single motor units (SMUs). Previously defined rules of SMU activation would predict that units of the same muscle (or at least of the same neuromuscular compartment) are activated homogeneously with activity peaks in the same "best" direction(s). In the present study, the best directions of SMUs in human biceps (both heads) and deltoid (anterior, medial, and posterior portions) were determined by measuring the firing rate and threshold force of units for recruitment during isometric force ramps in many different directions. For all muscles studied, neighboring motor units could have significantly different best directions, suggesting that each muscle receives multiple directional commands. Furthermore, 17% of the units sampled clearly had a second-best direction, consistent with a convergence of different directional commands onto the same motoneuron. The best directions of the units changed gradually with location in the muscle. Best directions did not cluster into separate groups, thus, not supporting the existence of clearly distinguished neuromuscular compartments. Instead, the results reveal a more gradually distributed activation of the biceps and deltoid motoneuron pools. A model is proposed in which the central control mechanism optimizes the fulfillment of the continuously changing directional force requirements of a movement by gradually recruiting and derecruiting those units ideally suited for the production of the required force vector at any given time.

Adult↗

PubMed1997

Postural dependence of muscle actions: implications for neural control.

The neural control of reaching entails the specification of a precise pattern of muscle activation distributed across the many muscles of the arm. Musculoskeletal geometry limits the possible solutions to this problem. Insight into the nature of this constraint was obtained by quantifying the postural variation in the mechanical actions of six human shoulder muscles. Estimates of muscle mechanical actions were obtained by electrically stimulating muscles to the point of contraction and recording the resulting forces and torques with a six-degree-of-freedom force-torque transducer. In a given experiment, data were obtained for up to 29 different arm postures. The mechanical actions of each muscle varied systematically with arm posture, regardless of the frame of reference used to define these actions. The nature of this dependence suggests that a relatively simple strategy can be used by the nervous system to account for the changing mechanical actions of arm muscles.

Adult↗

PubMed1997

Anticipatory and sequential motor control in piano playing.

Pianists were asked to play short excerpts from several pieces on an electronic keyboard. In each piece, there were two phrases whose first few notes were played identically with the right hand. Thereafter, the two phrases were played differently. The aim of the investigation was to ascertain whether or not hand and finger kinematics diverged prior to the depression of the last common note. Such a divergence would imply an anticipatory modification of sequential movements of the hand, akin to the phenomenon of coarticulation in speech. The lack of such a divergence would imply a strictly serial organization of movement sequences with one hand, as was found previously to be the case for typing. The time at which each key was depressed and released and the speed with which the key was depressed was recorded via a MIDI interface to a laboratory computer. The motion of the right wrist and of the fingers of the right hand was recorded optoelectronically. Piano playing can invoke anticipatory modifications of hand and finger kinematics. The time at which two patterns of movements diverged varied considerably from piece to piece. Playing an ascending scale with the requirement of a "thumb-under" maneuver could evoke an anticipatory modification as much as 500 ms in advance of the last common note. In another piece, keypresses appeared to be executed in a strict serial ordering and a third piece gave results intermediate between these two extremes. We interpret the results to suggest that a strict serial execution of a movement sequence is favored as long as this is compatible with the demands of the task.

Fingers↗

PubMed1997

Flexibility and repeatability of finger movements during typing: analysis of multiple degrees of freedom.

The kinematics of the hand and fingers were studied during various keystrokes in typing. These movements were defined by 17 degrees of freedom of motion, and methods were developed to identify simplifying strategies in the execution of the task. Most of the analysis was restricted to the 11 degrees of freedom of the fingers, neglecting thumb and wrist motion. Temporal characteristics of the motion were defined by computing principal components, and it was found that only a few (two to four) principal components were needed to characterize motion of each of the degrees of freedom. Hierarchical relationships among patterns within and between different degrees of freedom were identified using cluster analysis. There was a considerable amount of consistency each time a given keystroke was executed by a subject, and this repeatability may imply a reduction in the number of degrees of freedom independently controlled by the nervous system. However, there also appears to be considerable flexibility in the coordination of the many joints of the hand when examined across different keys and across different subjects.

Biomechanical Phenomena↗

PubMed1997

Evaluating an integrated musculoskeletal model of the human arm.

A simplified model of the mechanical properties of muscle and of the musculoskeletal geometry was used to predict torques at the shoulder and elbow during arm movements in the sagittal plane. Subjects made movements to 20 targets spaced on the diameter of a circle centered on the initial location of the hand. Movement kinematics and the electromyographic (EMG) activity of nine shoulder and elbow muscles were recorded. Muscle force was predicted using rectified EMG activity as an input to a Hill-type model of muscle dynamics. The model also made simplifying assumptions about muscle geometry. Muscle force was then converted to torque and the individual muscle torques were weighted to provide the best fit to the joint torque computed from the kinematic data. The overall fit of the model was reasonably good, but the goodness of fit was not uniform over all movement directions. The results suggest that the assumptions about the musculo-skeletal geometry, the model of muscle dynamics, and muscles not included in the analysis all contributed to the error.

Adult↗

PubMed1996

Basic features of phasic activation for reaching in vertical planes.

The purpose of this study was to fully characterize the timing and intensity of the phasic portion of the electromyographic (EMG) waveform for reaching movements in vertical planes. Electromyographic activity was simultaneously recorded from nine superficial elbow and/or shoulder muscles while human subjects made rapid arm movements. Hand paths comprised 20 directions in a sagittal plane and 20 directions in a frontal plane. In order to focus on the more phasic aspects of muscle activation, estimates of postural EMG activity were subtracted from the EMG traces recorded during rapid reaches. These postural estimates were obtained from activity recorded during very slow reaches to the same targets. After subtraction of this postural activity, agonist or antagonist burst patterns were often observed in the phasic EMG traces. For nearly all muscles and all subjects, the relation between phasic EMG intensity and movement direction was a function with multiple peaks. For all muscles, the timing of phasic EMG bursts varied as a function of movement direction: the data from each muscle exhibited a gradual temporal shift of activity over a certain range of directions. This gradual temporal shift has no obvious correspondence to the mechanical requirements of the task and might represent a neuromuscular control strategy in which burst timing contributes to the specification of movement direction.

Adult↗

PubMed1996

Force path curvature and conserved features of muscle activation.

This study examined the patterns of muscle activity that subserve the production of dynamic isometric forces in various directions. The isometric condition provided a test for basic features of neuromuscular control, since the task was analogous to reaching movement, but the behavior was not necessarily shaped by the anisotropy of inertial and viscoelastic resistance to movement. Electromyographic (EMG) activity was simultaneously recorded from nine elbow and/or shoulder muscles, and force pulses, steps, and ramps were monitored using a transducer fixed to the constrained wrists of human subjects. The force responses were produced by activating shoulder and elbow muscles; response direction was controlled by the relative intensity of activity in muscles with different mechanical actions. The primary objective was to characterize the EMG temporal pattern. Ideally, synchronous patterns of phasic muscle activation (and synchronous dynamic elbow and shoulder torques) would result in a straight force path; asynchronous muscle activation could result in substantial force path curvature. For both pulses and steps, asynchronous muscle activation was observed and was accompanied by substantial force path curvature. A second objective was to compare phasic and tonic EMG activity. The spatial tuning of EMG intensity was similar for the phasic and tonic activities of each muscle and also similar to the spatial tuning of tonic activity in a previous study where the arm was stationary but unconstrained.

Adult↗