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Biomedical subjects

C Bard

Publications and source records attributed to C Bard.

At least 19 recordsLinked to original sources
PubMed2001

Long-term brain metabolic alterations in exogenous Cushing's syndrome as monitored by proton magnetic resonance spectroscopy.

The effects of exogenous Cushing's syndrome on the brain metabolism were investigated by proton magnetic resonance spectroscopy (MRS). Thirteen patients having been treated for 2 to 22 years with prednisone were recruited. On the average, none of the metabolites (NAA, Cr, Cho and mI) were significantly different from those of 40 normal subjects in any of the three regions studied: frontal area, thalamus and temporal area. However, the Cho/H(2)O ratios were found to decrease significantly in the thalamic area as a function of treatment period (-1.3%/year). In the frontal and temporal areas, decreases of the Cho/H(2)O ratios were measured with treatment period but they did not reach statistical significance. Effects on Cho levels can be related to those observed for patients with endogenous Cushing's syndrome and suggest an impairment at the membrane level. The Cho/H(2)O reductions were not found to be dose- or age-dependent. Other metabolite ratios did not vary with treatment period, dose or age.

Adult↗
PubMed2001

Coordination in childhood: modifications of visuomotor representations in 6- to 11-year-old children.

This research investigated the development of visuomotor coordination in childhood, more specifically the conversion of visual information into motor sequences. Three groups of children (aged 6, 8 and 11 years) and a group of adults performed pointing movements without direct feedback from their arm displacements. Visual information, provided by a video camera, was disturbed by rotations of 0 degree, 45 degrees, 90 degrees, 135 degrees or 180 degrees. Six-year-old children showed poor accuracy for 180 degrees rotations. These results suggest that the youngest children use unidirectional representations to convert visual information into motor sequences. At 8 years of age, children showed a shift from unidirectional to bidirectional representations, as reflected by reduced errors for 180 degrees rotations. Eleven-year-old children and adults showed the same type of representations, i.e., bidirectional. However, as reflected by their slower movement time and slower modifications in temporal accuracy across trials, the oldest children have not yet reached maturation in their adaptive process when compared to adults.

Adaptation, Physiological↗
PubMed2001

A severe frontal-parietal lobe syndrome following cerebellar damage.

We report a case study of a frontal and parietal lobe syndrome with memory loss after unilateral left-sided cerebellar damage caused by a stroke in a patient with right cerebellar unusual developmental agenesis. The syndrome consisted of severe deficits in planning an organized sequence of events, in visuo-constructive abilities and inappropriate jocularity. These changes are ascribed in part to cerebellar-pontine lesions with resulting frontal lobe diaschisis as documented by single-photon emission computed tomography in the absence of morphological damage to the neocortex.

Adult↗
PubMed2001

Visual context and the control of movements through video display.

The aim of this experiment was to test the influence of target context on adaptation to scale perturbations introduced by a video display. Participants performed pointing movements without direct vision of their moving hand, although they could see their movements on a video display. Their perceived movements could be reduced, enlarged. or displayed at their actual size. Three target contexts were compared: dark surround, illuminated frame, and familiar object. Movements were executed with or without vision of hand displacement. Results showed that target context enhanced an allocentric coding of the movement, which improved movement execution. However, the effect of target context changed whether or not the displacement of the hand was available. Overall, the results suggest that target context allowed the extraction of dynamic information about movements, which is used to program and control movements. This suggests that target context could be used efficiently to improve spatial accuracy and speed in teleoperation learning. Potential applications include the reduction of difficulties encountered during teleoperation learning through the introduction of visual context.

Adolescent↗
PubMed2000

Recovery of the brain choline level in treated Cushing's patients as monitored by proton magnetic resonance spectroscopy.

In a previous study from our group [A. Khiat, C. Bard, A. Lacroix, J. Rousseau, Y. Boulanger, Brain metabolic alterations in Cushing's syndrome as monitored by proton magnetic resonance spectroscopy, NMR Biomed. 12 (1999) 357-363], proton magnetic resonance spectroscopy (1H MRS) was used to evaluate changes in cerebral metabolites in patients with Cushing's syndrome as compared to normal subjects. Data recorded in the frontal, thalamic and temporal areas demonstrated statistically significant decreases of the Cho/Cr ratios in the frontal and thalamic areas but not in the temporal area for Cushing's syndrome patients. No statistically significant changes in the NAA/Cr ratios were measured in any of the areas studied. In this follow-up study, MRS data are reported for ten patients after correction of hypercortisolism which demonstrate a statistically significant recovery of the choline levels in the frontal and thalamic areas. No variation in the NAA, Cr and mI metabolite ratios relative to H(2)O could be measured. Results are interpreted as an inhibition of the phosphatidylcholine degrading phospholipases by glucocorticoids which disappears after correction of hypercortisolism.

Adult↗
PubMed2000

The effects of spatial movement components precues on the execution of rapid aiming in children aged 7, 9, and 11.

The aim of the present study was twofold: first, to investigate the effects of spatial precues on the execution of rapid aiming in children aged 7, 9, and 11 and second, to provide a kinematic support to the investigation of the role of precues in aiming tasks performed under temporal constraints. Four precuing conditions were used, where participants received: (a) no precue of any type, (b) advance information on direction, (c) advance information on amplitude, and (d) complete information on the forthcoming movement. Our results showed that precuing the spatial dimensions of movement shortens reaction times, that such shortening is a function of the number of precued parameters, and that spatial precues modify the kinematics of the children's rapid aiming movements. Peak velocity increased with direction and/or amplitude, suggesting that precues play a significant role in motor preparation. Moreover, the accuracy results indicate that direction precuing induces a proactive directional regulation. Finally, direction and amplitude appear to be independently specified in children.

Attention↗
PubMed2000

Patterns of music agnosia associated with middle cerebral artery infarcts.

The objective of the study is to evaluate if the rupture of an aneurysm located on the middle cerebral artery (MCA) results in disorders of music recognition. To this aim, 20 patients having undergone brain surgery for the clipping of a unilateral left (LBS), right (RBS) or bilateral (BBS) aneurysm(s) of the MCA and 20 neurologically intact control subjects (NC) were evaluated with a series of tests assessing most of the abilities involved in music recognition. In general, the study shows that a ruptured aneurysm on the MCA that is repaired by brain surgery is very likely to produce deficits in the auditory processing of music. The incidence of such a deficit was not only very high but also selective. The results show that the LBS group was more impaired than the NC group in all three tasks involving musical long-term memory. The study also uncovered two new cases of apperceptive agnosia for music. These two patients (N.R. and R.C.) were diagnosed as such because both exhibit a clear deficit in each of the three music memory tasks and both are impaired in all discrimination tests involving musical perception. Interestingly, the lesions overlap in the right superior temporal lobe and in the right insula, making the two new cases very similar to an earlier case report. Altogether, the results are also consistent with the view that apperceptive agnosia results from damage to right hemispheric structures while associative agnosia results from damage to the left hemisphere.

Adult↗
PubMed1999

Modulation of anticipatory postural adjustments in a reactive and a self-triggered mode in humans.

Five subjects raised their preferred arm until horizontal in one of two experimental conditions: (1) in response to a visual signal (reactive condition), and (2) in a self-triggered condition. In both conditions, subjects were instructed to execute the movement at approximately 80% of their maximal velocity, such that all movements were nearly similar. EMG activity was recorded in a focal muscle (Anterior Deltoidus) and in three postural muscles (ipsi-lateral Gastrocnemius, contra-lateral Tensor Fascia Latae and ipsi lateral Semitendinosus) known to be activated prior to the focal muscle. Results showed greater anticipatory postural adjustments in the self-triggered than in the reactive condition for the three postural muscles. It is suggested that similar intentional movements can be triggered by different timing strategies.

Adult↗
PubMed1999

Brain metabolic alterations in Cushing's syndrome as monitored by proton magnetic resonance spectroscopy.

Proton magnetic resonance spectroscopy ((1)H MRS) was used to evaluate changes in cerebral metabolites in 13 patients with Cushing's syndrome (including seven with pituitary corticotroph adenomas and six with primary adrenal disease) as compared to 40 normal subjects. Data were recorded in the frontal, thalamic and temporal areas; quantification of the MRS signals demonstrated a statistically significant decrease of the Cho/Cr ratio in the frontal and thalamic areas but not in the temporal area for patients with Cushing's syndrome. The largest decrease in Cho/Cr was measured in the thalamic area of patients with a Cushing's syndrome secondary to an adrenal disease. No statistically significant changes in the NAA/Cr ratio were measured in any of the areas studied. These results suggest that the quantification of choline levels could be helpful for monitoring the cerebral metabolite alterations in patients with hypercortisolism.

Adult↗
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

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↗
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↗