Biomedical subjects

Thierry Pozzo

Publications and source records attributed to Thierry Pozzo.

16 recordsLinked to original sources

PubMed2006

Kinematic adaptation of locomotor pattern in rheumatoid arthritis patients with forefoot impairment.

Rheumatoid arthritis (RA) is a leading cause of disability, which affects primarily the forefoot. Moreover, the forefoot is the final ground body interface for transmitting forces produced by the plantar flexors in order to move the body forward. Therefore, a dysfunction in patients with arthritis might induce important changes in gait, such as modifications in the coordination between legs to correct a reduced range of motion (ROM) and to produce smooth stride motions. First, we wanted to investigate the modifications of gait parameters in order to get a deeper understanding of the locomotor adaptation after a distal joint impairment. Second, we wanted to extract the mechanisms used to compensate for these impairments. In order to carry out this study, RA patients with forefoot impairment and healthy subjects were asked to walk along a straight line at two different velocities and were recorded by a motion analysis system. Patients were able to produce an efficient pattern despite a reduction of the ROM of the forefoot. At normal speed, the substantial modification of the locomotor pattern was linked to the adaptation of the lower-limb segment coordination and to the loss of ROM. Compensative mechanisms are the results of an efficient adaptation that offset the effect of the lesions. In contrast, at high speed, all of the kinematic modifications observed at natural speed vanished. It seems that pain and its associated sensory signals help to update the motor command and compel patients to adjust the descending command to the altered representation of distal mobility. Finally, the mechanical consequences of these changes are of particular interest since different levels of force exerted at the hip, knee and ankle might result in a supplementary structural alteration of these joints.

Adaptation, Physiological↗

PubMed2006

Static postural control in children with developmental dyslexia.

The present investigation tries to better understand potential association and causal relationship between phonological and postural impairment due to developmental dyslexia. The study included 50 boys with developmental dyslexia and selected on the basis of their overall reading difficulties, and 42 control boys. Body sway during a quite standing posture eye open and eye closed on a force platform were tested in the two groups of subjects that were between 10 and 13 years of age. Analysis of classical parameters quantifying the centre of pressure (CP) displacements along antero-posterior and lateral axes showed a significant difference between the two groups. Dyslexic children showed on average greater instability, with greater length, variability and mean power frequency of CP displacements with or without vision. Our results demonstrate that postural parameters may discriminate between children with dyslexia and age-equivalent controls.

Adolescent↗

PubMed2006

Kinematic features of movement tunes perception and action coupling.

How do we extrapolate the final position of hand trajectory that suddenly vanishes behind a wall? Studies showing maintenance of cortical activity after objects in motion disappear suggest that internal model of action may be recalled to reconstruct the missing part of the trajectory. Although supported by neurophysiological and brain imaging studies, behavioural evidence for this hypothesis is sparse. Further, in humans, it is unknown if the recall of internal model of action at motion observation can be tuned with kinematic features of movement. Here, we propose a novel experiment to address this question. Each stimulus consisted of a dot moving either upwards or downwards, and corresponding to vertical arm movements that were masked in the last part of the trajectory. The stimulus could either move according to biological and or non-biological kinematic laws of pointing tasks. We compared subjects' estimations of the stimulus vanishing or final positions after biological and after non-biological motion displays. Subjects systematically overestimated the vanishing and final position for the two directions (up and down) and the two kinematics displayed (biological and non-biological). However, estimation of the final position decreased in precision and increased in variability for movements that violated the kinematic laws of arm pointing task. The results suggest that motion inference does not rely only upon visual extrapolating mechanisms based on past visual trajectory information. We propose that motion estimation relies on internal models that contain specific kinematic details of vertical arm movement, which can be rapidly recalled during motion observation.

Adult↗

PubMed2005

Mentally represented motor actions in normal aging. I. Age effects on the temporal features of overt and covert execution of actions.

The present study examines the temporal features of overt and covert actions as a function of normal aging. In the first experiment, we tested three motor tasks (walking, sit-stand-sit, arm pointing) that did not imply any particular spatiotemporal constraints, and we compared the duration of their overt and covert execution in three different groups of age (mean ages: 22.5, 66.2 and 73.4 years). We found that the ability of generating motor images did not differentiate elderly subjects from young subjects. Precisely, regarding overt and covert durations, subjects presented similarities for the walking and pointing tasks and dissimilarities for the stand-sit-stand task. Furthermore, the timing variability of imagined movements was always greater compared to actual movements and was of the same amount in the three groups of age. In the second experiment, we investigated the effect of age (three groups with mean ages: 22, 64.8 and 73.2 years) upon temporal characteristics of covert and overt movements involving strong spatiotemporal constraints (speed/accuracy trade-off paradigm). During overt execution young and elderly subjects respected Fitts's law despite the fact that movement speed progressively decreased with age. Thus, while execution is deteriorated, the motor preparation process is still intact in old age, and follows well-known laws of biological motions. For covert execution, movement speed progressively decreased with age but elderly subjects did not respect Fitts's law. This suggests that the generation and control of motor intentions that consciously do not come to execution, particularly those concerning complex motor actions are progressively perturbed in the aging brain.

Adult↗

PubMed2005

Human whole-body reaching in normal gravity and microgravity reveals a strong temporal coordination between postural and focal task components.

Previous experiments by our group in normal gravity (1 G) have revealed spatial relationships between postural and focal components of whole-body reaching and pointing movements. We suggested that these relationships could be explained partly through the use of gravity to displace the CoM and attain the object or target position. In this study we compared human whole-body reaching in 1 G and microgravity (0 G) in order to more fully investigate how gravity contributes to strategies adopted for task execution and to determine possible invariant temporal relationships between multiple segments. Whole-body reaching movements made from the standing position in two experimental conditions of execution speed (naturally paced and as fast as possible) were recorded during periods of 1 G and 0 G in parabolic flight. Overall, at each speed of reaching, movement times were significantly slower when performed in 0 G than in 1 G for two of the three subjects, but all subjects were able to produce significantly faster movements in 0 G than in 1 G. Despite similar general trends across subjects observed in 1 G, angular displacements of reaching movements performed in 0 G differed greatly between subjects. There were changes at all joints, but above all at the shoulder and the ankle. However, despite a high intersubject and intratrial variability in 0 G, in both gravity conditions all subjects demonstrated times to peak curvilinear velocity for the finger (end effector) and the whole-body centre of mass (CoM) that coincided, regardless of the speed of execution. Moreover, cross-correlations between multiple segment curvilinear velocities and those of the CoM revealed tight, highly correlated temporal relationships between segments proximal to the CoM (which was expected). However, for more distal segments, the correlations were weaker, and the movements lagged behind movements of the CoM. The major and most interesting finding of this study was that although the finger was the most distal within the segment chain, with respect to the CoM, it was highly correlated with the CoM (0.99--0.98, all conditions) and with no time lag. Despite the large intersubject and inter-environmental variability recorded in this study, temporal relationships between postural task components (CoM displacements) and those of the focal movement (end-effector trajectory) were consistently conserved.

Acclimatization↗

PubMed2004

Recovery of the locomotor function after prolonged microgravity exposure. I. Head-trunk movement and locomotor equilibrium during various tasks.

Recovery of locomotor function was investigated in seven cosmonauts exposed to microgravity for 6 months. Crew members executed a locomotor task with visual cues (eyes open, EO) and without them (eyes closed, EC). The locomotor task consisted of ascending a two-step staircase, jumping down from a 30-cm high platform, and finally walking 4 m in the straight-ahead direction. Subjects were tested before the flight (D-30), and on the second day (R+2) and the sixth day (R+6) after the flight. Cosmonauts succeeded in all locomotor sub-tasks as early as R+2. In particular, microgravity exposure did not prevent cosmonauts from producing a straight walking trajectory even when blindfolded (deviation at R+2 with EO 2.0+/-0.7 degrees, and with EC 4.7+/-1.9 degrees ). However, lateral movements of trunk were found to be increased at R+2 (16%), suggesting post-flight gait instability. Modifications of the timing of forward trunk movements were also detected at R+2. Unexpectedly, coordination patterns between head and trunk movements remained unchanged. The maximum amplitude of head pitches was 5 degrees or less. Yet, the cosmonauts held their heads at lower positions at R+2 in comparison with their pre-flight postures, and they lowered their heads even further during blindfolded locomotion. In general, comparable spatial and temporal modifications of head and trunk movements at R+2 were observed during the stair and gait cycles. Mean values of locomotor descriptors measured at R+6 did not deviate from the pre-flight baseline. When performing jumps after the return from their flight, cosmonauts decreased the amplitude and speed of head rotation by approximately 50% in comparison with the pre-flight values. In addition, the timing of head pitches was uncertain after weightlessness. All the above changes endured at R+6. Previous studies reported that prolonged exposure to microgravity adversely affects the motor performance in the initial hours upon re-entry to Earth. However, gait analysis revealed that cosmonauts recovered near-optimal locomotor abilities as early as the second day post-flight. Results suggest a notable capability of the central nervous system to rapidly accommodate to changing physical environment and body properties. The role of head stabilization at a lower position is conjectured to be an adaptive response to microgravity-induced motor disorders.

Adaptation, Physiological↗

PubMed2004

Gait-dependent motor memory facilitation in covert movement execution.

In the current study, we examined whether sensorimotor information stored in short-term memory may influence the temporal features between overt and covert execution of human locomotor movements and, furthermore, to examine to what extent such influence may depend on the ongoing gait activity. The subjects (n=20) who participated in the experiment were separated in two groups and instructed to walk (overt execution) or imagine walking (covert execution) along three locomotor paths: horizontal, uphill and downhill. The subjects of the first group, labeled in block, performed all the covert trials before executing the corresponding overt trials, while the subjects of the second group, labeled in serial, alternated between overt and covert movements. The overt and covert durations were recorded by means of an electronic stopwatch. We found high temporal similarities between overt and covert execution for both groups and for all the locomotor paths. Nevertheless, the execution of imagined movements was more variable compared to their actual counterparts. In addition, timing variability of covert movements was smaller for the group in serial compared to the group in block. This decrease in timing variability was larger for the horizontal walking compared to uphill or downhill locomotion. Furthermore, linear regression analysis performed on the data of the group in serial showed close temporal relationships between each successive overt and covert execution. These relationships were stronger when walking along the horizontal vs. sloped paths. Therefore, our results on timing variability provide evidence for gait-dependent motor memory facilitation in covert movement execution. We propose that gait-dependent contribution of sensory feedback information to movement regulation may account for these findings.

Adult↗

PubMed2004

Whole body pointing movements in transient microgravity: preliminary results.

The aim of the present study is a better comprehension of strategies of motor coordination during complex movements. In this field of research microgravity represent a unique experimental condition for the investigation of the role of equilibrium control in movement planning. Namely, here we focus on two important issues: the centre of mass control and the endpoint trajectory. Preliminary results of the center of mass position and the finger path curvature during pointing movements performed under normal and transient microgravity conditions are presented.

Adaptation, Physiological↗

PubMed2003

Gait-dependent integration of neck muscle afferent input.

We investigated the integration of neck muscle afferents during walking and running. Subjects walked or ran straight ahead, with or without an additional mass (20% of body weight). They performed all trials without vibration and with continuous vibration (80 Hz) applied to the lateral aspect of the neck. Vibration systematically caused body deviation toward the side opposite to the stimulation. The amplitude of vibration-induced body deviations was dramatically larger for walking (21.6 +/- 4.6 degrees ) than for running (8.0 +/- 2.5 degrees ). The additional mass marginally straightened body trajectory (average 5.6%), indicating that the gait-dependent effect of neck vibration cannot solely be attributed to differences in body inertia between walking and running. We concluded that neck muscle afferences are selectively gated according to the gait performed.

Adult↗

PubMed2003

Comparison of actual and imagined execution of whole-body movements after a long exposure to microgravity.

Five cosmonauts were tested 30 days before a six-month space flight and also on the 2nd and the 6th day after their return to Earth. Cosmonauts performed and imagined a task that involved climbing two stairs to step onto a platform, jumping down with both feet and walking normally for a distance of 4 m. Durations of actual and imagined movements were measured by an electronic stopwatch. Results indicated that cosmonauts performed actual and imagined movements with similar durations before and after the space flight. However, the 2nd day after their return to Earth, cosmonauts significantly increased the durations of both actual and imagined movements. The durations of the imagined and actual movements returned to approximate pre-flight values 6 days after landing. Our results provide evidence that motor imagery process accurately replicates the neural and mechanical modifications which occur during the re-adaptation of the motor system on Earth's gravito-inertial environment after a long space flight.

Adaptation, Physiological↗

PubMed2002

Trajectories of arm pointing movements on the sagittal plane vary with both direction and speed.

Five subjects performed arm upward and downward movements at different speeds (movement duration ranged from 0.26 to 1.2 s). Fingertip paths, velocity profiles and muscle activation patterns of arm and forearm were computed. Inspection of the electromyograph (EMG) revealed that for relatively slow speeds (>0.7 s) and for both directions, only the flexor muscles were active, mainly the anterior deltoid, for motor (upward) and braking action (downward) respectively. However, where gravity was no longer sufficient to accelerate downward and decelerate upward movements (<0.7 s), both flexors and extensors muscles were active. Path curvature and position of maximum deviation from straightness were lower for downward than for upward movements. In addition, the position of maximum deviation from straightness became progressively higher with increase in duration for both upward and downward movements. The ratio of acceleration duration to total movement duration was greater for downward than upward directions for all the range of speeds. The ratio of maximum to mean velocity was similar for upward and downward movements but decreased with decrease in speed. The results indicate that the brain accomplishes arm movements in the vertical plane with different planning processes for movements with or against gravity. Furthermore, they provide evidence that both gravitational and inertial forces are determinant for arm trajectory generation in the vertical plan.

Adult↗

PubMed2002

Prolonged exposure to microgravity modifies limb endpoint kinematics during the swing phase of human walking.

Many neurophysiological and behavioural studies suggested that the lower limb endpoint might be a centrally represented variable within the gravity reference frame and effectively controlled during the locomotion. This investigation examines the effects of prolonged exposure to microgravity upon lower limb endpoint kinematics. Seven cosmonauts were tested before and the 2nd day after a 6 month orbital mission. The spatio-temporal patterns of the limb extremity (malleolus) were analysed during the swing phase of the walk using a motion analysis system. Paths and velocity profiles of endpoint displacements were computed and compared for both the pre- and post-flight walking sessions. The results indicated significant modifications in both spatial and temporal features the 2nd day after re-entry on Earth. The step was significantly lengthened, and its shape was altered, presenting higher vertical component compared with the pre-flight values. The acceleration duration was increased whereas the swing duration remained invariant whatever the walking session. These modifications in endpoint kinematics could partly but not completely be explained by peripheral factors like muscle atrophy or plasticity at the spinal level. We suggest that, apart of changes in peripheral level, central modifications concerning internal models of gravity, putatively used to plan limb motion, might have induced such locomotor changes.

Biomechanical Phenomena↗

PubMed2002

Does order and timing in performance of imagined and actual movements affect the motor imagery process? The duration of walking and writing task.

The purpose of the present study was to investigate the effects on the duration of imagined movements of changes in timing and order of performance of actual and imagined movement. Two groups of subjects had to actually execute and imagine a walking and a writing task. The first group first executed 10 trials of the actual movements (block A) and then imagined the same movements at different intervals: immediately after actual movements (block I-1) and after 25 min (I-2), 50 min (I-3) and 75 min (I-4) interval. The second group first imagined and then actually executed the tasks. The duration of actual and imagined movements, recorded by means of an electronic stopwatch operated by the subjects, was analysed. The duration of imagined movements was very similar to those of actual movements, for both tasks, regardless of either the interval elapsed from the actual movements (first group) or the order of performance (second group). However, the variability of imagined movement duration was significantly increased compared to variability of the actual movements, for both motor tasks and groups. The findings give evidence of similar cognitive processes underlying both imagination and actual performance of movement.

Adult↗

PubMed2002

Coordination between equilibrium and hand trajectories during whole body pointing movements.

We examined the coordination between equilibrium and voluntary pointing movements executed from the standing position, using the whole body. It has previously been shown that trunk movement has little effect upon kinematic characteristics of hand pointing when movements are executed in the sitting position. The present study asked if elements of hand trajectory are modified by requirements of large trunk displacements and fine equilibrium control when pointing movements are executed from the standing position. To achieve this, center of pressure (CoP) and center of mass (CoM) displacements were analyzed along with the kinematics of the pointing hand. Results showed that the CoM was not stabilized (it displaced between 23% and 61+/-21% of the foot's length), confirming that instead of a compensation of mechanical perturbations due to arm and trunk movements, the present equilibrium strategy consisted of controlling CoM acceleration towards the target. Hand paths were curved and were not distance or speed invariant. Rather than simple inefficiencies in programming or execution, path curvature suggested that different hand movement strategies were chosen as a function of equilibrium constraints. In light of these results, we hypothesize that postural stability may play a role in the generation of hand trajectory for complex, whole-body pointing movements, in addition to constraints placed upon end-effector kinematics or the dynamic optimization of upper-limb movements. A dependent regulation of equilibrium and spatial components of the movement is proposed.

Acoustic Stimulation↗

PubMed2002

Imagined and actual arm movements have similar durations when performed under different conditions of direction and mass.

Several experiments have suggested that similar physiological substrates are involved in movement execution and motor imagery, and that the same laws of movement control apply to both processes. Using a mental chronometry paradigm, we examined the effects of movement direction and added mass on the duration of actual and imagined movements. Six subjects executed or imagined arm movements in the sagittal and horizontal plane, in three different loading conditions: without added mass, and with an added mass of 1 and 1.5 kg. The duration of both actual and imagined movements was measured by an electronic stopwatch. The actual movements were significantly increased in duration as a function of mass, for both movement directions. However, direction per se had no effect on duration. The duration of imagined movements was very similar to that of actual movements whatever the subject and mass and direction condition. These results show that both inertial and gravitational constraints are accurately incorporated in the timing of the motor imagery process, which appears therefore to be functionally very close to the process of planning and performing the actual movement.

Adult↗

PubMed2002

Head position during various locomotor executions after prolonged microgravity exposure.

Head orientation in the sagittal plane was assessed before and the second and sixth days after a prolonged microgravity exposure (6 months) in 7 astronauts, which were instructed to execute various locomotor movements (stair ascent, jump down and level walk). Crewmembers systematically flexed down the head when they executed the locomotion the second day post-flight compared to the pre-flight walk. Cephalic orientation was normally positioned when movements was performed the sixth day after Earth re-entry. This head flexion may reflect a strategy used by cosmonauts to increase the vestibular sensibility, and then improve the control of the dynamic equilibrium during locomotor movements. The high rate of re-adaptation indicated that cosmonauts rapidly recovered their normal walking capacities despite the prolonged microgravity exposure.

Journal Article↗