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Biomedical subjects

A Berthoz

Publications and source records attributed to A Berthoz.

At least 19 recordsLinked to original sources
PubMed1992

Effect of post-training unilateral labyrinthectomy in a spatial orientation task by guinea pigs.

The effects of unilateral labyrinthectomy in guinea pigs have been studied on an angular orientation task consisting, in an open field, of running to a hidden goal oriented at 45 degrees with respect to the cephalocaudal axis of the animal placed in a starting-box. The task was conducted in light but in an homogeneous environment, i.e. without visual, auditory or olfactory cues indicating the location of the goal. A second group of animals was submitted to a similar task running to a hidden goal but the place of the goal was indicated by a colored card. All the animals were trained before the lesion and tested in their respective task for 1 month after the lesion. In the task conducted without conspicuous cues, animals were dramatically disturbed. In contrast, animals pretrained in the visually guided task were not impaired after the lesion. These results point out the important role of vestibular information in performing spatial tasks based on angular estimation, since, even if proprioceptive and visuokinesthetic information remain available, subjects seemed not able to maintain a correct angular trajectory. The trajectories being not disturbed in the visually guided task, one can exclude the hypothesis that such deficit was due to a purely motor disturbance.

Animals↗
PubMed1991

A neural network model of sensoritopic maps with predictive short-term memory properties.

Coordinated orienting movements can be accurately performed without direct sensory control. Ocular saccades, for instance, have been shown to be reprogrammed after target disappearance when an intervening eye movement is electrically triggered before the saccade onset. Saccadic eye movements can also be executed toward memorized targets, even when the subject has been passively moved in darkness. Two hypotheses have been proposed to account for this goal-invariance property: either (i) the goal is reconstructed and memorized in the stable frame of reference linked to the environment ("allocentric, coordinates") or (ii) the goal is selected and memorized in the sensors-related maps ("egocentric coordinates") and is continuously updated by efferent copies of the motor commands. In this paper, we shall describe a formal neural network based on this second hypothesis. The results of the simulation show that target position can be memorized and accurately updated in a topologically ordered map, using a velocity-signal feedback. Moreover, this network has been submitted to a simple learning procedure by using the intermittent visual recurring afferent signal as the teaching signal. A similar mechanism could be involved in control of limb movement.

Computer Simulation↗
PubMed1991

Eye and head coupled and dissociated movements during orientation to a double step visual target displacement.

Tight coupling between eye and head movements has been observed in response to a single visual target offset. On this basis, when the visual stimulus consists of two successive steps in the same (horizontal) direction, either increasing in eccentricity (staircase) or decreasing in eccentricity (pulse-step) gaze should be due to concomitant eye and head angular displacement. That is, the eyes and head should aim at each target displacement so that their combined movement matches target offset. We have tested this hypothesis in five healthy subjects. The measured variables were head and gaze offset, the interval between two consecutive saccades from onset to onset (I) and the response delay between onset of the second step and onset of the first gaze saccade (D). With both staircase and pulse-step stimuli, the eye saccade preceded the head movement, and the gaze response either had the stimulus profile pattern or consisted of one gaze saccade to the final target offset. In response to staircase stimuli, I decreased concomitantly with an increase in D; with pulse-step stimuli, as D increased, I decreased slightly in three subjects and decreased markedly in two subjects. Dissociation between the eye and head movements could clearly be demonstrated with pulse-step stimuli: the first gaze saccade to the target pulse displacement was accompanied by a head movement to the target step offset. We also observed cases in which the gaze saccade to the target step displacement was made simultaneously with the head movement to the target pulse offset. Our study extends previous observations in head fixed condition and illustrates that in the majority of cases, when the head is free and a visual pulse step stimulus is presented, both the saccadic and head systems have the ability to modify or cancel the initial neural command to move to the first target displacement. When this modification takes place in only one system, eye and head movements are dissociated.

Electrooculography↗
PubMed1991

Head stabilization during various locomotor tasks in humans. II. Patients with bilateral peripheral vestibular deficits.

This experiment, which extends a previous investigation (Pozzo et al. 1990), was undertaken to examine how head position is controlled during natural locomotor tasks in both normal subjects (N) and patients with bilateral vestibular deficits (V). 10 normals and 7 patients were asked to perform 4 locomotor tasks: free walking (W), walking in place (WIP), running in place (R) and hopping (H). Head and body movements were recorded with a video system which allowed a computed 3 dimensional reconstruction of selected points in the sagittal plane. In order to determine the respective contribution of visual and vestibular cues in the control of head angular position, the 2 groups of subjects were tested in the light and in darkness. In darkness, the amplitude and velocity of head rotation decreased for N subjects; these parameters increased for V subjects, especially during R and H. In darkness, compared to the light condition, the mean position of a line placed on the Frankfort plane (about 20-30 degrees below the horizontal semi-circular canal plane) was tilted downward in all conditions of movement, except during H, for N subjects. In contrast, this flexion of the head was not systematic in V subjects: the Frankfort plane could be located above or below earth horizontal. In V subjects, head rotation was not found to be compensatory for head translation and the power spectrum analysis shows that head angular displacements in the sagittal plane contain mainly low frequencies (about 0.3-0.8 Hz). The respective contribution of visual and vestibular cues in the control of the orientation and the stabilization of the head in space is discussed.

Adult↗
PubMed1991

Eye-head coupling in humans. II. Phasic components.

A tonic coupling between the horizontal component of eye position and dorsal neck muscle activity has been demonstrated in animals and humans. In addition, a transient saccade related coupling has been found in animals. In order to investigate such a phasic component of the eye-head synergy in humans, we have recorded the activity of isolated motor units in the splenius muscle during large horizontal eye movements in head fixed subjects. Eye movement recording was achieved by conventional binocular electro-oculography and the activity of the right splenius muscle was recorded with Bronks coaxial electrodes inserted manually at the C4-C5 intervertebral level. We found two main types of motor unit discharge patterns in the splenius (SPMU), the first type (type A, 14 SPMUs) shows a phasic modulation of firing rate during saccades with a triphasic profile composed of a pre-saccadic suppression, a per-saccadic burst and a post saccadic tonic discharge proportional to eye position. The second type (type B, 6 SPMUs) exhibits little, if any, modulation of firing rate with either fixation or saccades. These results suggest that eye-head coupling is present not only during the fixation period but also during saccades and that a phasic activity or suppression related to saccadic eye velocity is present in dorsal neck muscle EMG.

Adult↗
PubMed1991

Head stabilization during locomotion. Perturbations induced by vestibular disorders.

Head kinematics was studied in 10 normal subjects (NS) and 7 patients (P) with bilateral vestibular deficit while they executed various locomotor tasks. The movement of the body was recorded with a video system which allowed a computer reconstruction of the motion of joint articulations and other selected points on the body in three dimensions. Analyses focus on head translation along the vertical axis and rotation in the sagittal plane. Two conditions were studied: free walking (W) and hopping (H). The subjects were tested in light and in darkness. In NS, while walking in darkness, mean head position was tilted downward. In contrast, this flexion was not systematic in P. Darkness did not significantly influence the amplitude and velocity of head angular displacement during W, but, during H the amplitude decreased by 37% for NS. During H in darkness, head stabilization decreased for P. These results suggest that head kinematics, during natural locomotor tasks, could be used to evaluate vestibular deficiencies.

Adult↗
PubMed1990

Head stabilization during various locomotor tasks in humans. I. Normal subjects.

Head kinematics were studied in ten normal subjects while they executed various locomotor tasks. The movement of the body was recorded with a video system which allowed a computer reconstruction of motion of joint articulations and other selected points on the body in three dimensions. Analyses focus on head translation along the vertical axis and rotation in the sagittal plane. This was done by recording the displacement of a line approximating the plane of horizontal semi-circular canals (the Frankfort plane: F-P). Four conditions were studied: free walking (W) walking in place (WIP) running in place (R) and hopping (H). In the 4 experimental conditions, amplitude and velocity of head translation along the vertical axis ranged from 1 cm to 25 cm and 0.15 m/s to 1.8 m/s. In spite of the disparities in the tasks regarding the magnitude of dynamic components, we found a significant stabilization of the F-P around the earth horizontal. Maximum amplitude of F-P rotation did not exceed 20 degrees in the 4 situations. Vertical angular velocities increased from locomotion tasks to the dynamic equilibrium task although the maximum values remained less than 140 degrees/s. Predominant frequencies of translations and rotations in all the tasks were within the range 0.4-3.5 Hz and harmonics were present up to 6-8 Hz. During walking in darkness, mean head position is tilted downward, with the F-P always below the earth horizontal. Darkness did not significantly influence the amplitude and velocity of head angular displacement during W, WIP and R, but during H the amplitude decreased by 37%. Residual head angular displacement is found to compensate for head translation during the 4 conditions. Our study emphasizes the importance of head stabilization as part of the postural control system and described as a basis for inertial guidance.

Adult↗
PubMed1989

Head kinematic during various motor tasks in humans.

Head kinematic during various motor tasks was studied in ten subjects. The movement of the body was recorded with a video system (E.L.I.T.E.) which allows a computer reconstruction of three-dimensional motion of selected points on the body. Analysis is focused on head rotation in the horizontal and vertical planes. The results demonstrate that the amplitude and the maximum velocity do not exceed respectively 38 deg/s and 185 deg/s. However the head is intermittently stabilized and the angle of this stabilization is dependent upon the task and related to the direction of gaze. Darkness had no significant effect on head rotational velocity during walking but caused a decrease in velocity during running and hopping. The results suggest that head stabilization (1) is related to an ocular fixation point in the direction of gaze in space and (2) is probably regulated on the basis of a predictive mode of sensory motor control.

Adult↗
PubMed1989

Neural correlates of horizontal vestibulo-ocular reflex cancellation during rapid eye movements in the cat.

1. The aim of the present study is to describe the behaviour of identified second-order vestibular neurones in the alert cat during eye saccades. A selection of neurones which are involved in horizontal eye movements has been made. The activity has been compared with a selected sample of abducens motoneurones recorded in the same animals. 2. Alert head-fixed cats were used for this study. Eye movements were recorded by the scleral search coil technique. Abducens motoneurones were identified by antidromic stimulation from the VIth nerve with chronically implanted electrodes. They were recorded extracellularly. 3. Second-order vestibular neurones were identified by orthodromic stimulation from the vestibular organs. They were recorded intra-axonally and injected with horseradish peroxidase after recording of their physiological characteristics. Their morphology was reconstructed from frozen sections. 4. All the recorded vestibular neurones showed various amounts of eye position sensitivity. The firing rate (F) - horizontal eye position (H) characteristics are compared for abducens and vestibular neurones. The population average values are F = 33 + 4 H for motoneurones and F = 51 + 2.4 H for vestibular neurones. 5. All recorded vestibular neurones showed an increase of discharge rate during contralateral horizontal saccades and a strong decrease or pause during ipsilateral saccades. Firing rate - horizontal eye velocity sensitivity has been calculated. 6. Results suggest a strong inhibitory input on vestibular neurones from the saccadic generator. This mechanism underlies the suppression of the vestibulo-ocular reflex during saccades. Our results suggest that in the cat, for saccades of amplitude smaller than 20 deg, there is a variable degree of suppression which is provided by a projection of excitatory bursters (EBNs) on second-order vestibular neurones through inhibitory type II neurones. 7. We also conclude from this study that the eye position sensitivity of vestibular second-order neurones is in fact a motor signal indicating a motor error, i.e. the amount of head or eye movement which remains to be done in order to align gaze on target with the eyes centred in the orbit.

Abducens Nerve↗
PubMed1989

[Cooperation and substitution of the saccadic system and the reflexes of vestibular origin: should the "reflex" concept be revised?].

Neuronal mechanisms of production of ocular saccadic movements are discussed, together with stabilizing movements of vestibular origin, and descriptions given of several neuronal elements constituting the tecto-reticulo-spinal system, the generator of horizontal saccadic movements in the brain stem, the vestibulo-ocular pathway, etc... Analysis of these pathways and of the signals travelling through them suggests that the overall apparatus is not constituted of isolated reflex modules but acts as a true functional unit for cooperation between orientation and stabilization mechanisms. In addition, coordination of synergies between eye and head movements appear to be based on the activity of clearly identifiable neurons. This neuronal implementation of the concept of synergy is completed further by a remarkable functional flexibility. The latter allows substitution by the brain, for example, fo saccades instead of vestibular reflex movements when the latter are deficient because of lesions or disturbances in the coherence of sensory information. The principal conclusion reached is that cognitive factors, which imply representations of body movements in space activated as a function of the subject's goals, must be considered when ocular movement, and gaze control is described.

Animals↗
PubMed1979

Otolithic-acoustic interaction in the control of eye movement.

In order to examine otolithic contribution to eye movements ten subjects were asked to track either a moving acoustic target or a stationary target during subject linear motion on a cart. The relative displacement between the subject and the target was the same in the two situations. Recordings of eye movements during subject lateral acceleration in the dark without any task, or with the task of tracking an imagined stationary target were made as a control. The frequencies ranged between 0.15 and 0.3 Hz and peak acceleration between 0.55 and 1.2 m/s2. No lateral eye movements (L-nystagmus) were recorded in the dark. Only saccadic eye movements were recorded during the tracking of a moving acoustic target. Slow eye movements interspersed by saccades were observed when the moving subject tracked an imagined or an acoustic stationary target. Contribution of the slow phase to tracking was more important in the presence of an acoustic target than in the presence of imagined target. The results are interpreted in terms of an otolithic contribution to the central reconstruction of the acoustic target velocity, or in terms of an adaptive control of the otolithic-ocular reflex gain. A conceptual model accounting for these interpretations is proposed.

Acoustic Maculae↗
PubMed1979

Dynamic role of vision in the control of posture in man.

The influence of moving visual surround on the manitenance of upright posture has been studied in man during combined motion of a platform (cart) on which subjects were standing. The normal visual surround was either moving together with the cart, or with a velocity equal to cart velocity either in the same or in the opposite direction of car motion (cart acceleration was either 0.2 m/s2 or 0.05 m/s2). The changes in body pitch observed under these three conditions of visual surround motion were in the same direction as those observed when visual surround motion was given in isolation. However, their amplitude was greater, particularly when visual surround motion was in conflict with body motion.

Acceleration↗
PubMed1979

Contribution of vision to muscle responses in monkey during free-fall: visual stabilization decreases vestibular dependent responses.

In a previous study the muscle responses from the lower limbs were studied in the Baboon (Papio-Papio) during sudden falls. On the other hand, recent findings concerning the role of vision in the control of posture during rapid perturbations in man have stimulated the present investigation. EMG activities were recorded from the fully conscious animal using chronic electrodes implanted in various muscles (splenius, quadriceps femoris, soleus, and tibialis anterior). For testing, the monkey was seated in a special chair suspended from an electromagnet and unexpectedly dropped 90 cm. EMG responses were recorded in three randomly presented conditions: with normal motion of visual world (N), with visual world stabilized with respect to the head (S) using a box covered inside by a black and white checkboard pattern surrounding the animal's head, and in total darkness (D). Results showed that condition S is accompanied in all tested muscles by a significant decrease in the EMG response; this effect is particularly evident in the interval 60--120 ms but may occur earlier. Condition D is in most of the cases accompanied by a less important decrease which is situated between condition N and condition S. These results are in contrast to previous concludions of other authors which negated the role of vision in similar situations.

Animals↗
PubMed1979

Electroanatomy of tectal efferent connections related to eye movements in the horizontal plane.

1. Excitatory and inhibitory oligosynaptic pathways from the superior colliculus (CS) to ocular motoneurons engaged in horizontal eye movements were investigated in cats using acute and chronic brain stem transections in combination with intracellular recordings. 2. Isolation of the medial ponto-bulbar tegmentum from vestibular nuclei and adjacent lateral tegmental structures did not impair short-latency EPSPs and IPSPs induced by collicular stimulation in lateral rectus motoneurons (LR-MNs). On the contrary, responses were enhanced after chronic de-efferentation of vestibular nuclei. This suggests compensatory synaptic rearrangement in the tecto-reticulo-abducens pathways. 3. Midsagittal mesencephalic transections eliminated not only crossed excitatory but also ipsilateral inhibitory CS action on LR-MNs indicating that underlying pathways undergo decussation within the midbrain. 4. Midsagittal transections at different pontine and bulbar levels were performed to locate the second decussation of the inhibitory pathway. Ipsilateral IPSPs were eliminated only by deep lesions extending for about 1.5 mm rostral and caudal to the 6th nuclei. 5. Investigation of medial rectus motoneurons (MR-MNs) revealed two types of excitatory responses to CS-stimulation: (a) di- or trisynaptic EPSPs characterized by a fast rising phase and pronounced frequency potentiation; (b) slowly rising EPSPs displaying little or no frequency potentiation. 'Fast' EPSPs were abolished by all types of pontine lesions interrupting transmission through the contralateral 'abducens region' and may thus be relayed by internuclear neurons within or adjacent to the 6th nucleus. 'Slow' EPSPs persisted after transverse sections at midpontine and rostral pontine levels. 6. The trajectory of tectofugal inhibitory pathway to MR-MNs could not be followed due to a marked suppression of IPSPs under pentobarbital anesthesia. Persistence of IPSPs in LR-MNs under same conditions indicated that reciprocal inhibition of LR- and MR-MNs is mediated by different populations of inhibitory interneurons.

Animals↗