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Biomedical subjects

B Amblard

Publications and source records attributed to B Amblard.

36 records · Page 2Linked to original sources
PubMed1990

Early sensory determinants of locomotor speed in adult cats: I. Visual compensation after bilabyrinthectomy in cats and kittens.

After a study of locomotion in cats deprived of their vestibular receptors early in life, the average speed of locomotion was measured in 3 adult cats, first before and then several months after bilateral labyrinthectomy, in a task involving free locomotion across platforms, rails or ladders and under normal illumination versus stroboscopic illumination or darkness. In the absence of visual cues, cats which received lesions as adults showed, on both wide and narrow supports, the same speed deficits as those of subjects which underwent lesions soon after birth. Visual cues were, however, used by some cats with early lesions to recover near normal performances on wide platforms. Evidence was found that the vestibular deficit comprised at least 3 components: a severe loss of dynamic balance occurred in all subjects with lesions and was mostly not compensated for by vision; a loss of the ability to keep to a straight course in darkness was observed on wide platforms, but vision considerably improved this function, even under stroboscopic illumination; a slight paw adjustment deficit was also observed on irregular supports, due to the fact that vision played a decreased role after the vestibular lesion. These effects point to the specificity of the vestibular control of balance, the availability of several sensorimotor strategies for orientation, and the complementarity of vestibular and visual inputs in guiding the subjects' step. We confirm here that vestibular inputs do not play a critical role during locomotor development, and stress the fact that peripheral visual cues about position or orientation (rather than motion), play a leading role in compensatory strategies.

Afferent Pathways↗
PubMed1990

Early sensory determinants of locomotor speed in adult cats: II. Effects of strobe rearing on vestibular functions.

Cats raised under stroboscopic illumination are known to exhibit oculomotor and visuomotor deficits, but little is known about their locomotor abilities. Four strobe-reared cats with intact labyrinths were tested in a locomotor test involving various walking surfaces and various illumination conditions. Apart from their general slowness under all the experimental conditions, these strobe cats showed no special deficit on narrow rails, which indicates that their dynamic balancing abilities were normal. In these subjects, the decrease in the use of kinetic visual cues was roughly compensated for by an increase in the use of position cues. When tested after chronic bilateral labyrinthectomy, the strobe-reared cats' locomotor speeds were identical to those of control labyrinthectomized cats, except on wide platforms involving orientation towards a visual goal. These results show that in the absence of motion-vision, vestibular control of dynamic balance can mature normally, but they suggest that other aspects of locomotion involving the processing of vestibular and kinesthetic inputs may be impaired.

Aging↗
PubMed1989

Discrete visual samples may control locomotor equilibrium and foot positioning in man.

The static or dynamic visual cues required for equilibrium as well as for foot guidance in visually guided locomotion in man were studied using a variety of locomotion supports and illumination and visual conditions. Stroboscopic illumination (brief flashes) and intermittent lighting (longer flashes) were used to control and to vary the visual sampling frequency of static (positional/orientational) visual cues. There were three main findings: First, visual control of foot positioning during locomotion over a narrow support depends mainly upon the availability of high frequency static visual cues (up to about 12 Hz); and third, static visual cues required for equilibrium control are extracted from both the peripheral and the central visual field. Assuming that discrete demands for feedback occur, a simple probabilistic model was proposed, according to which the mean time that elapses following presentation of static visual cues about positions or changes of position accounts for the differences in the difficulty of the various illumination conditions.

Journal Article↗
PubMed1987

Response properties of area 17 neurons in cats reared in stroboscopic illumination.

The response properties of 196 area 17 cells were studied qualitatively in seven cats reared from birth in a stroboscopically illuminated environment (frequency, 2/s; duration, 200 microseconds). Quantitative testing with the multihistogram technique was carried out in 115 cells. As control population, 453 neurons recorded in area 17 of the normal adult cat and tested qualitatively (of which 301 neurons were tested quantitatively) were available. In area 17 of strobe-reared cats, a number of spatial characteristics of receptive fields investigated with hand-held stimuli were found to be abnormal. There was a strong reduction in the encounter frequency both of end-stopped cells and of binocularly driven cells in the strobe-reared cats. Central receptive fields in strobe-reared cats were wider than in normal cats, but the increase in receptive-field width with eccentricity was still observed. More cells than in normal cats showed either no selectivity or only a weak bias for stimulus orientation, but the orientation tuning of orientation-selective cells was similar in strobe-reared and normal cats. Quantitative testing revealed that the velocity preference of cells in area 17 subserving central vision was different in strobe-reared cats from that of normal cats, due to a reduction in the encounter frequency of cells showing a preference for low velocities. There was no difference in velocity preference between strobe-reared and normal cats in the parts of area 17 that subserve peripheral vision, the proportion of neurons responding to fast velocities showing a similar increase in both groups of animals. Fewer cells were direction selective in strobe-reared cats than in normal cats. Most of the remaining direction-selective cells had peripheral receptive fields and the synergism between leaving an OFF subregion and entering an ON subregion contributed to their direction selectivity. Latency of neurons in area 17 of strobe-reared cats was slightly higher than in normal cats, but the response strength of neurons was the same in the two groups. The proportion of cells failing to respond to briefly flashed stationary stimuli was significantly lower in strobe-reared than in normal animals. Qualitative and quantitative testing showed that strobe rearing has a stronger effect on the parts of area 17 that subserve central vision than on those that subserve peripheral vision. Comparing the present results with those of Kennedy and Orban (37) shows that strobe rearing has less effect on area 17 than on area 18 and that the functional differences between areas 17 and 18 in strobe-reared cats are smaller than in normal cats.

Animals↗
PubMed1985

Lateral orientation and stabilization of human stance: static versus dynamic visual cues.

The differential contributions of static versus dynamic visual cues to postural control were studied in human subjects. Lateral body oscillations were measured with accelerometers located at head, hips and ankle levels, while subjects righted their balance under various mechanical conditions: on either a soft (foam rubber) support or a hard one, and in either the classical or the sharpened Romberg stance. The visual pattern (horizontal or vertical rectangular grating) was illuminated with either a stroboscopic bulb or a normal one, and control measurements were also taken in darkness for each mechanical condition. Acceleration signals were processed into their frequency power spectra, the mean area and shape of which were taken to characterize the postural skills involved and the effects of either the visual suppressions or the mechanical destabilizations. Although dynamic visual cues have already been found to play a major role in the control of lateral body sway (Amblard and Crémieux 1976), we demonstrate here that static visual cues, the only ones available under stroboscopic illumination, also make a clear though minor contribution. Hence we suggest the existence of two modes of visual control of lateral balance in man, which are well separated in terms of the frequency range of body sway: the first mechanism, which operates below 2 Hz and is strobe-resistant, seems to control the orientation of the upper part of the body; the second mechanism, which operates above 4 Hz, centers on about 7 Hz and is strobe-vulnerable, seems to immobilize the body working upwards from the feet. Thus static visual cues may slowly control re-orientation or displacement, whereas dynamic visual cues may contribute to fast stabilization of the body. In between the frequency ranges at which these two visuomotor mechanisms come into play, at about 3 Hz, there is what we call a "blind frequency", a visually neutral sway frequency which may arise from the incompatibility of visual reorientation with visual stabilization, and where vision appears unable to reduce postural sway to any marked extent. Transmission of the destabilization produced by suppression of visual cues or by mechanical methods from one anatomical level to another is also briefly discussed in terms of bio-mechanical constraints, and the correlations between various pairs of levels are considered.

Adult↗
PubMed1984

Locomotion in adult cats with early vestibular deprivation: visual cue substitution.

Four cats labyrinthectomized shortly after birth ( DELAB ) exhibited the classical vestibular syndrome and recovery, while their motor development was otherwise unimpaired. As adults, they were tested for visual vestibular substitution in a locomotor task with either orientation requirements (tilted platforms) or balance requirements (narrow platforms). Visual motion cues or static visual cues were controlled using normal or stroboscopic lighting, or darkness. Measurements of the average speed of locomotion showed that: - Although all cats increase their speed when more visual cues become available, a marked deficit occurs in darkness only in the DELAB cats. - With either vestibular cues alone or static visual cues alone, cats are able to reach the same level of performance in the tilted platform test, which suggests a total visual-vestibular interchangeability in orientation. - DELAB cats perform very poorly in the narrow rail test. - When continuous vision is allowed in the narrow rail test the DELABs ' performance rises but does not match that of the control group. - A specific deficit in balance for the DELAB group is thus reduced by normal continuous vision as compared to stroboscopic vision, suggesting a significant, though imperfect, substitution of motion visual cues for the missing dynamic vestibular cues. - Dynamic visual cues play only a minor role in most situations, when locomotory speed is high. This results support the view that both the vestibular and the visual system can subserve two distinct functions: - dynamic information may stabilize the stance in narrow unstable situations, during slow locomotion, - and static orientation cues may mainly control the direction for displacement. Possible interactions between head positioning and body orientation in the DELAB cats are discussed.

Animals↗
PubMed1980

Afferent visual pathways and receptive field properties of superior colliculus neurons in stroboscopically reared cats.

Unit recordings were made in the superior colliculus of strobe-reared cats. Receptive field properties were studied and electrical stimulation in the chiasma and optic tract made it possible to characterize the visual input. The retinal Y-cell input and the cortical input were found to be deficient. The principal response deficit was the decrease of selective response to direction of movement, also shown to be largely absent in the corticotectal pathway. These results are compared to similar findings in dark-reared animals and discussed in connection with the importance of visual movement to the developing visual system.

Animals↗
PubMed1980

Role of foveal and peripheral visual information in maintenance of postural equilibrium in man.

In a previous report (Amblard & Crémieux, 1976) we demonstrated that the maintenance of postural equilibrium, measured with the subject in Mann's stance on a foam rubber support, was significantly more difficult under stroboscopic rather than normal lighting conditions. The most plausible cause of the difficulty is the subject's loss of visual perception of movement as a result of the stroboscopic lighting. The present study was designed to look at this factor under normal lighting conditions. Also, the relative contributions of foveal and peripheral vision were assessed. During stance, the subjects (5 women and 6 men, aged from 25 to 55 yr.) viewed either a horizontal or a vertical rectangular grating. With horizontal lines, the visual perception of lateral movement is minimized. Lateral acceleration was measured at three anatomical levels: ankles, hips, and head. The horizontal stripe condition was significantly less effective than the vertical stripe one for maintenance of balance, both for measurements at the head level only and for values averaged from all three levels. Balance was significantly impaired with foveal vision alone compared to full vision or to peripheral vision alone, for measurements from each of the three levels. We conclude that the visual perception of movement is a very important factor in the maintenance of the equilibrium, peripheral vision playing the major role, and foveal vision only a supplementary one.

Adult↗
PubMed1979

Visually guided reaching in the cat reared in fixed or random frequency stroboscopic light.

The effect of deprivation of visual perception of movement in a visuo-motor task has been tested in cats reared in stroboscopic light since birth. Three cats were reared in light of fixed (2 flash/sec, flash duration 2 msec) and three in light of random (between 0.5 and 3.5 flash/sec) frequency. These 6 animals, together with 6 control cats, underwent (as adults) a test of visual control of reaching for a target with a paw, with operant conditioning. While the cats raised in fixed frequency stroboscopic conditions (FFS) showed no deficit, those raised in random frequency condition (RFS) exhibited significantly less precise guidance than FFS and control animals.

Animals↗
PubMedDate not supplied

Voluntary head stabilization in space during trunk movements in weightlessness.

The ability to voluntarily stabilize the head in space during lateral rhythmic oscillations of the trunk has been investigated during parabolic flights. Five healthy young subjects, who gave informed consent, were examined. The movements were performed with eyes open or eyes closed, either during phases of microgravity or phases of normal gravity. The main result to emerge from this study is that the head may be stabilized in space about the roll axis under microgravity conditions with, as well as without vision, despite the reduction of the vestibular afferent and the muscle proprioceptive inputs. Moreover, the absence of head stabilization about the yaw axis confirms that the degrees of freedom of the neck can be independently controlled, as it was previously shown. These results seem to indicate that voluntary head stabilization does not depend crucially upon static vestibular afferents. Head stabilization in space may be in fact organized on the basis of either dynamic vestibular afferents or a postural body scheme.

Head Movements↗
PubMedDate not supplied

Head-trunk coordination during hops using one or two feet in children and adults.

The main purpose of this study was to investigate the development of head-trunk coordination during single hops using one foot or two feet in children of two ages (5.5 to 6 and 7 to 7.5) and adults (n = 6/group). The kinematics of the subjects' hops were analyzed by means of an automatic optical TV-image processor called the ELITE system. The absolute angular dispersion of the head, trunk, and leg about the pitch and the roll axis were measured. Head and trunk pitch and roll anchoring indexes were calculated in order to compare the stabilization of a given segment with respect both to external space and to the underlying anatomical segment. Results were analyzed separately for 3 phases: take-off, flight, and landing. Only the last two phases, flight and landing, are presented in this paper, and the following was found: 1) During flight, under both unipedal and bipedal conditions, head and trunk stabilization in space about the pitch axis occurred in children as well as in adults, suggesting an articulated operation of the head-trunk unit. In contrast, during landing, in children and adults, head stabilization in space tended to disappear while trunk stabilization in space was still present, suggesting an en bloc operation of the head-trunk unit. Similarly, pelvis stabilization in space about the roll axis occurred in all subjects during both flight and landing under unipedal conditions, where lateral balance control is of primary importance. Taken together, these results suggest that head stabilization in space is phase dependent, while trunk stabilization is phase independent. The trunk, including the pelvis, may thus constitute a stable reference frame from which anteroposterior and lateral balance control is organized during hops. 2) For head-trunk coordination, whatever the component of rotation, the two groups of children differed from adults, but did not differ from each other, suggesting that, while jumping, the transition between 6 and 7 years of age in the organization of balance control takes place in the coordination of the lower limbs during the preparatory phase of the take-off.

Adult↗