Biomedical subjects

M Fleury

Publications and source records attributed to M Fleury.

At least 37 records · Page 2Linked to original sources

PubMed1999

Deafferentation and pointing with visual double-step perturbations.

The capability of reprogramming movement responses following changes in the visual goal has been studied through the double-step paradigm. These studies have shown that: (a) continuous internal feedback-loops correct unconsciously the dynamic errors throughout the movement; (b) proprioceptive information and/or the efference copy have a privileged status among central processes, insuring on-line regulation of the initial motor commands; and (c) generation of the motor program starts after target presentation, and is continuously updated in the direction of the current internal representation of the target, at least until the onset of hand movement. This main corrective process of the initial program appears to be basically independent of visual reafference from the moving hand. However, the agreement with the possibility of a visuomotor loop, based on the comparison of the new updated representation of the target position and on the information from the moving hand, has not determined whether the correcting process is proprioceptive feedback dependent, or whether internal feedback-loops (efferent copies) are responsible for quick corrections of unfolding motor responses. To answer this question, the present experiment investigated the pointing behavior of a deafferented subject, using a double-step paradigm under various conditions of visual feedback and movement initiation. Overall, the present study (a) clearly showed the capacity of the motor system to modify and correct erroneous trajectories on the mere basis of internal feedback-loops and (b) emphasized the crucial role played by the target jump/arm triggering delay and the importance of the eye efferent copy for providing information about the spatial goal of the movement.

Afferent Pathways↗

PubMed1999

Role of the feedforward command and reafferent information in the coordination of a passing prehension task.

The performances of a deafferented patient and five control subjects have been studied during a self-driven passing task in which one hand has to grasp an object transported by the other hand and in a unimanual reach-to-grasp task. The kinematics of the reach and grasp components and the scaling of the grip aperture recorded for the self-driven passing task were very similar in controls and the deafferented subject (GL). In contrast, for the unimanual task when vision was absent, GL's coordination between reaching and grasping was delayed in space and time compared with the control subjects. In addition, frequent reopening of the grip was observed in GL during the final closure phase of the unimanual prehension task. These results support the notion that afferent proprioceptive information resulting from the reaching movement - which seemed to be used to coordinate reaching and grasping commands in the unimanual task - is no longer necessary in the self-induced passing task. Finally, for the externally driven passing task, when the object was passively transported by the experimenter, the coordination was consistently modified in all subjects; grip aperture onset was delayed, thus asserting a specific contribution of the central command or feedforward mechanisms into the anticipation of the grasp onset observed in the self-driven passing task. The origin and nature of the information necessary for building up the feedforward mechanisms remains to be elucidated.

Adult↗

PubMed1999

How efficient are central mechanisms for the learning and retention of coincident timing actions?

We compared the adaptive strategy and retention capacity of a deafferented subject and control subjects when intercepting, with a sliding-throw, an apparent movement coming at various speeds. Subjects were submitted to five practice sessions (30 trials per session) and to a retention test. The throwing kinematics was analysed, and spatial and temporal performance errors were measured. With practice, the deafferented subject showed modifications in movement initiation strategies and throwing patterns. With a slow apparent movement, the deafferented subject's initial behavior was characterized by short movement initiation and movement times. With practice, she showed an important increase in movement time in session 5, allowing longer visual control and leading to better temporal and spatial accuracy than that shown in session 1. In the retention session, the deafferented patient showed a late movement initiation strategy, similar to that of the control subjects. This increased movement initiation time was accompanied by an improved temporal accuracy compared to the deafferented subject's early results. However, spatial accuracy improvement was labile and could not be maintained over the retention interval. At the fast speed, all temporal components of the response, namely, movement initiation time (MIT), movement time (MT), and disk travel time (DTT), were similar for the deafferented and control subjects. Overall, the deafferented subject reduced her temporal error through practice, though without attaining the control subjects' accuracy. However, with a fast-moving stimulus, she showed a deteriorated spatial accuracy, even doubling her spatial errors at retention. In brief, the deafferented subject achieved proper temporal (perceptivo-cognitive) lasting control of her interceptive action, whereas spatial (sensorimotor) regulation raised mnemonic problems.

Afferent Pathways↗

PubMed1999

Aging and postural control: postural perturbations caused by changing the visual anchor.

OBJECTIVE: To determine the effect of modifying the stable visual anchor on the postural stability of older individuals. The visual anchor was changed by opening doors similar to those found in an elevator cage. Lighting intensities inside and outside the cage were varied to create increasing or decreasing luminosity conditions. The effect of adding a cognitive load (counting backwards) was also tested. DESIGN: A controlled laboratory study. SETTING: Tests performed in a balance laboratory. MEASUREMENTS: Sensory and clinical measurements to insure the integrity of the central and peripheral nervous system. Measures of balance were derived from the recordings of the center of foot pressure. These measures included range and speed of the center of foot pressure. PARTICIPANTS: Eight older, community-dwelling subjects and nine young subjects participated. A sensorimotor evaluation was used to insure that all older individuals were free from any pathologies affecting postural stability. All participants had a low score (indicating high balance confidence) on the Falls Efficacy Scale and no history of falls. RESULTS: Older individuals were affected by modification of the stable visual anchor induced by the opening of doors similar to that of an elevator cage. They showed greater ranges of the center of foot pressure (COP) and speed of the COP after than before the opening of the doors. Furthermore, the increased ranges and speed were two to three times greater than that observed for the young subjects. A lighting intensity considered as comfortable for reading inside the elevator affected the overall postural stability of the older participants negatively. Counting backwards also decreased their overall stability. CONCLUSION: Changing the stable visual anchor, as when exiting an elevator cage, could be a significant risk factor for older persons. Moreover, when combined with a cognitive load or lower lighting intensity inside the elevator cage, the negative effects on the postural stability of older persons are exacerbated.

Accidental Falls↗

PubMed1998

Contribution of central and peripheral vision to the regulation of stance: developmental aspects.

Postural oscillations in 6-, 8-, and 10-year-old children were analyzed in four conditions of vision of the environment (complete vision, peripheral vision, central vision and no-vision) and two conditions of ankle somatosensory information (normal and altered support surfaces with a 5-cm-thick foam). Children were more stable with than without vision. This was observed whether children had complete or partial vision (central or peripheral). They were also more stable with the normal than with the altered support surface. Overall, there was no effect of age. Beyond these well-established results, the present experiment showed the complementary role of peripheral and central vision in the regulation of children's posture. For the 6- and 10-year-olds, central and peripheral vision yielded similar postural stability, whereas for the 8-year-olds, central vision yielded greater postural stability than peripheral vision. The analysis of postural oscillations in the medio-lateral and antero-posterior planes showed that, for the three age groups, central vision was as efficient whatever the plane. On the other hand, after age 6, peripheral vision was more efficient for regulating antero-posterior than medio-lateral oscillations. The contribution of the different sensory systems and their interaction for stabilizing posture in children should be specifically interpreted with regard to the operating characteristics of each sensory system at each age.

Age Factors↗

PubMed1998

Corrective loops involved in fast aiming movements: effect of task and environment.

In daily living, we continuously interact with our environment. This environment is rarely stable and living beings show remarkable adaptive capacities. When we reach for an object, it is necessary to localize the position of this object with respect to our own body before programming an adequate arm movement. If the target remains stable, the programmed movement brings the hand near the target. However, what happens when the target suddenly jumps to another position in space? The aim of this work was to investigate how rapid aiming movements are corrected when the target is displaced close to movement onset. Our results reveal that rapid movements can be modified and that the efficiency of trajectory amendments vary according to task (directional or direction/amplitude pointings) and environment (structured or darkness). We were most interested in the specific role played by peripheral and/or central feedback information (efferent copy) in the control of aiming movements. The results suggest that the two types of loops are complementary in movement regulation. However, their predominance varies according to the nature of the task at hand.

Adaptation, Physiological↗

PubMed1998

Survey of out-of-hospital emergency intubations in the French prehospital medical system: a multicenter study.

STUDY OBJECTIVE: To determine the clinical characteristics of endotracheal intubation in the French emergency prehospital medical system and compare these data with those of other systems. METHODS: This study was performed in lle de France (Paris Region) in mobile ICUs staffed by physicians. This prospective, descriptive study involved completion of a questionnaire by the operator just after endotracheal intubation was performed. RESULTS: Six hundred eighty-five (99.1%) of 691 consecutive prehospital intubations were performed successfully in the field. The orotracheal route was used in 96.0%, and no surgical approaches such as cricothyroidotomy were used. Mechanical complications occurred in 84 patients, at a rate of 15.9% for nonarrest patients and 8.1% for arrest patients. A wide variety of sedation protocols were used. Difficult intubations (10.8%) were comparable in incidence to the number seen in US emergency departments, not US prehospital systems. By the same token, intubation success rates (99.1%) were comparable to US EDs and much higher than US prehospital results. CONCLUSION: The characteristics of French prehospital airway management differ significantly from those of other countries. These differences may be explained by differences in approach to prehospital management rather than differences of skill.

Clinical Protocols↗

PubMed1998

Target speed alone influences the latency and temporal accuracy of interceptive action.

When intercepting a mobile object or an apparent movement, participants show a temporal bias. They are in advance when dealing with a slow-moving stimulus and late with a fast-moving one. We studied participants intercepting an apparent movement by sliding a disk on a table. Using a fast and a slow stimulus speed, we varied three factors: duration of presentation of the stimulus, distance covered by the stimulus, and speed context (constant or varied) of stimulus presentation. In addition to the temporal bias, spatial accuracy and kinematic measures were collected. The temporal bias created by speed was evident across all three factors. Speed, in addition to strongly determining the temporal bias, significantly affected the throwing strategy adopted by the participants, as revealed by latency, movement time, and disk trajectory duration.

Adult↗

PubMed1997

Optimization of glottic exposure during intubation of a patient lying supine on the ground.

Two methods of endotracheal intubation of patients lying on the ground were compared for ease and speed of intubation and minimization of complications in a crossover study of prehospital-oriented emergency physicians. Intubation of a mannequin was attempted by the physicians in either a left lateral decubitus (LLD) position or a kneeling (K) position, followed by the alternate position. The LLD position afforded more rapid intubation, better glottic visualization, and less dental trauma. Eighty-seven percent of physicians completely visualized the glottis in the LLD position, versus 33% of the K position group. Intubation times were 10.5 versus 14.6 seconds in the LLD and K positions, respectively (P < .001). The LLD position is a more effective position (in a mannequin model) than the K position for intubation of patients found lying on the ground, a frequent situation in prehospital care.

Cross-Over Studies↗

PubMed1997

Sampling concerns in scanline algorithms.

This paper investigates the problem of providing suitable interpolation for scanline algorithms. These algorithms are of interest, as they are parallelizable. A structure for analyzing the problem is given. The theory in regard to resampling is developed in the context of a scanline algorithm for image rotation. The theory is compared to results arrived at in practice. Alternative interpolation schemes are discussed, including the use of a cubic Hermite interpolator. The paper points to theoretical limitations of scanline algorithms.

Algorithms↗

PubMed1996

Control of single-joint movements in deafferented patients: evidence for amplitude coding rather than position control.

Two deafferented patients and several control subjects participated in a series of experiments to investigate how accurate single-joint movements are programmed, spatially calibrated, and updated in the absence of proprioceptive information. The deafferented patients suffered from a permanent and severe loss of large sensory myelinated fibers below the neck. Subjects performed, with and without vision, sequences of forearm supinations and pronations with two temporal delays between each movement (0 s and 8 s). Overall, the lack of proprioception did not yield any significant decrease in movement accuracy when vision was available. Without vision, the absence of proprioceptive afferents yielded (1) significantly larger spatial errors, (2) amplitude errors similar to those of control subjects, and (3) a significant drift when an 8-s delay was introduced between two successive movements. Subjects also performed, without vision, a 20 degrees supination followed by a 20 degrees pronation that brought back the wrist to the starting position. On some trials, the supination was blocked unexpectedly by way of a magnetic brake. When the supination was blocked, subjects were already on the second target and no pronation was required when the brake was released. The deafferented patients, unaware of the procedure, always produced a 20 degrees pronation. These data confirm that deafferented patients were not coding a final position. It rather suggests that they coded an amplitude and translated the spatial distance between the two targets in a corresponding force pulse. Overall, the results highlight the powerful and key role of proprioceptive afferents for calibrating the spatial motor frame of reference.

Adult↗

PubMed1996

Availability of visual and proprioceptive afferent messages and postural control in elderly adults.

The ability of young and elderly adults to keep a stable upright posture while facing changes in the availability of visual and/or propriomuscular information was investigated. The two sensory sources of information were alternatively available and withdrawn, jointly and separately, during 10-s alternating sequences. Vision was modified by means of liquid-crystal goggles, and proprioception was altered by means of tendon vibration of both antagonistic ankle muscles. Elderly adults were less stable than young adults when vision was withdrawn. Both groups were greatly affected when propriomuscular inputs were altered by vibration. Under constant visual conditions and following a propriomuscular perturbation (i.e., vibration), elderly adults were unable to take advantage of the reinsertion of propriomuscular inputs. They showed a transient, decreased stability and were unable to fully recover during a 10-s period, whereas young adults were able to rapidly integrate the information to stabilize their posture. When both propriomuscular and visual inputs were withdrawn and concurrently reinserted, the elderly adults did not show a transitory increase in the velocity of the center of foot pressure. The present results extend findings on the inability of elderly adults to reconfigure rapidly the postural set following reinsertion of sensory inputs. The results also suggest that elderly adults have difficulties in taking advantage of sensory redundancy in postural control.

Adult↗

PubMed1996

Gait problems in diabetic neuropathic patients.

OBJECTIVE: To examine whether a reduced peripheral sensibility caused by diabetic neuropathy increases the attentional demands necessary for controlling and regulating gait. DESIGN: Nonrandomized control trial. SETTING: University motor performance laboratory. SUBJECTS: Twelve diabetic patients with peripheral neuropathy and 7 control subjects, all volunteers. INTERVENTIONS: All subjects first performed a control seated reaction time task. For the walking task, auditory stimuli were randomly presented in the third, fourth, or fifth walking cycle on left foot toe off on left foot heel contact. The subject's task was to respond verbally as fast as possible to the auditory stimulus, while maintaining progression. MAIN OUTCOME MEASURES: Simple reaction times and kinematics of the gait pattern (cycle amplitude, cycle duration, cycle speed, cadence and percentage of time spent in the single support phase) were evaluated. RESULTS: For the walking task, diabetic neuropathic patients had a smaller cycle amplitude, cycle speed, and percentage of time spent in the single support phase than control subjects. Also, reaction times while walking were higher for diabetic neuropathic patients than for control subjects. CONCLUSIONS: Diabetic neuropathic patients show a less destabilizing and more conservative gait than control subjects. The increased attentional demands in gait for the diabetic neuropathic patients, along with their more conservative gait pattern, suggest that a lack of proprioception from the legs affects the control of gait. Diminished sensory information makes gait control more cognitively dependent in diabetic neuropathic persons than in control subjects.

Aged↗

PubMed1996

Age-related differences in the integration of sensory information during the execution of a bimanual coordination task.

Young (n = 7) and elderly (n = 7) subjects performed bimanual coordination patterns in the transverse plane according to the in-phase or antiphase mode. Sensory information was manipulated through visual (with or without vision of the limbs) and proprioceptive input (with or without vibratory stimuli on one limb). Movement patterns with vibrations showed higher deviations from the intended relative phase than did those without vibrations. This finding suggests that the proprioceptive information induced by the vibrations and the movement interfered, leading to a disruption of the coordination patterns. In addition, as compared with the elderly, the young subjects performed more stable movements under normal circumstances but were more strongly affected by vibratory stimuli during the performance of in-phase movements. During antiphase movements, both age groups experienced a decrease of pattern stability. Furthermore, the absence or presence of visual feedback influenced the performance of the young subjects more than that of the elderly. The presence of vision led to stable in-phase movements, whereas a decrease of pattern stability was observed for antiphase movements. In general, these results demonstrate that manipulation of feedback sources affects young subjects more than elderly ones, and this can be related to a reduced sensory sensitivity as a function of aging.

Journal Article↗

PubMed1996

PEL, a 'new' high-frequency red cell surface antigen.

A 'new', inherited, high-frequency blood group antigen has been named PEL and is numbered 901014. Two PEL-propositi with anti-PEL have been found, both French-Canadians. Two other French-Canadian propositi with very weak expression of PEL on their red cells have an antibody, provisionally named anti-MTP, which does not react with PEL-cells.

Adult↗

PubMed1996

Gait of a deafferented subject without large myelinated sensory fibers below the neck.

We evaluated the gait pattern of a deafferented subject who suffered a permanent loss of large sensory myelinated fibers below the neck following an acute episode of purely sensory neuropathy 21 years ago. The subject has developed several strategies to achieve a secure gait, namely: (1) a reduction of the degrees of freedom by freezing the knee articulations during the stance phase, (2) a preservation of body balance by enlarging his base of support, and (3) visual monitoring of his step by stabilizing the head-trunk linkage together with a characteristic forward tilt. As a result, the gait of the deafferented subject lacks the fluidity of normal gait. Compared with normal subjects, the gait pattern of the deafferented subjects is characterized by a shorter cycle length, a longer cycle duration, a slower speed, and a lower cadence. Using a dual-task paradigm, the attentional demands for walking were particularly important (as indexed by longer probe reaction times) during the double-support phase, suggesting that the deafferented subject uses the double-support phase as a transitory stable phase to update cognitively the postural features necessary for generating his next step.

Denervation↗

PubMed1995

Visual stability with goal-directed eye and arm movements toward a target displaced during saccadic suppression.

This experiment tested whether the perceived stability of the environment is altered when there is a combination of eye and visually open-loop hand movements toward a target displaced during the eye movements, i.e., during saccadic suppression. Visual-target eccentricity randomly decreased or increased during eye movements and subjects reported whether they perceived a target displacement or not, and if so, the direction of the displacement. Three experimental conditions, involving different combinations of eye and arm movements, were tested: (a) eye movements only; (b) simultaneous eye and rapid arm movements toward the target; and (c) simultaneous eye and arm movements with a restraint blocking the arm as soon as the hand left the starting position. The perceptual threshold of target displacements resulting in an increased target eccentricity was greater when subjects combined eye and arm movements toward the target object, specially for the no-restraint condition. Subjects corrected most of their arm trajectory toward the displaced target despite the short movement times (average MT = 189 ms). After the movements, the null error feedback of the hand's final position presumably overlapped the retino-oculomotor signal error and could be responsible for the deficient perception of target displacements. Thus, subjects interpreted the terminal hand positions as being within the range of the endpoint variability associated with the production of rapid arm movements rather than as a change of the environment. These results suggest that a natural strategy adopted for processing spatial information, especially in a competing situation, could favour a constancy tendency avoiding systematic perception of a change of environment for any noise or variability at the central or peripheral levels.

Adult↗

PubMed1995

Weight judgment. The discrimination capacity of a deafferented subject.

A weight discrimination study was undertaken to test (i) the capacity of controls and a deafferented subject (deprived of large sensory myelinated fibres from nose down), to discriminate weights with and without vision; (ii) the capacities of observers to discriminate weights while watching the deafferented and control subjects' lifting movements; (iii) the contribution of supplementary sources of sensory information (e.g. vestibular afferents) to the deafferented subject's discrimination capacity. With vision, G.L.'s liminal discrimination of weights was similar to that of the controls. In contrast, precluding vision impaired massively, but not completely, G.L.'s discrimination capacity, so emphasizing the importance of visual kinaesthetic cues in G.L. and incidently the importance of large myelinated sensory function in weight discrimination in controls. Kinematics recordings of G.L.'s lifting movements with vision revealed a significant correlation between weight and peak velocity of the lifting movement. This reflects a specific strategy used by G.L. to generate movements, allowing her to judge the weight of a lifted object visually. Peak velocity rather than amplitude of movement appears to be the main cue for G.L. since there was a lack of correlation between amplitude and weight lifted. For controls, none of the correlations (weight versus amplitude or weight versus velocity) was significant, whether vision was available or not. When watching G.L.'s lifting performance, external observers were able to use similar cues to establish their judgments, but they were far less accurate in doing so when watching control subjects. This suggests that controls were using a strategy different from G.L.'s.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗