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A Berthoz

Publications and source records attributed to A Berthoz.

At least 19 recordsLinked to original sources
PubMed2006

Effect of gravity on human spontaneous 10-Hz electroencephalographic oscillations during the arrest reaction.

Electroencephalographic oscillations at 10 Hz (alpha and mu rhythms) are the most prominent rhythms observed in awake, relaxed (eye-closed) subjects. These oscillations may be considered as a marker of cortical inactivity or an index of the active inhibition of the sensory information. Different cortical sources may participate in the 10-Hz oscillation and appear to be modulated by the sensory context and functional demands. In microgravity, the marked reduction in multimodal graviceptive inputs to cortical networks participating in the representation of space could be expected to affect the 10-Hz activity. The effect of microgravity on this basic oscillation has heretofore not been studied quantitatively. Because the alpha rhythm has a functional role in the regulation of network properties of the visual areas, we hypothesised that the absence of gravity would affect its strength. Here, we report the results of an experiment conducted over the course of 3 space flights, in which we quantified the power of the 10-Hz activity in relation to the arrest reaction (i.e., in 2 distinct physiological states: eyes open and eyes closed). We observed that the power of the spontaneous 10-Hz oscillation recorded in the eyes-closed state in the parieto-occipital (alpha rhythm) and sensorimotor areas (mu rhythm) increased in the absence of gravity. The suppression coefficient during the arrest reaction and the related spectral perturbations produced by eye-opening/closure state transition also increased in on orbit. These results are discussed in terms of current theories on the source and the importance of the alpha rhythm for cognitive function.

Adult↗
PubMed2006

Reproduction of self-rotation duration.

The vestibular system detects the velocity of the head even in complete darkness, and thus contributes to spatial orientation. However, during vestibular estimation of linear passive self-motion distance in darkness, healthy human subjects mainly rely on time, and they replicate also stimulus duration when required to reproduce previous self-rotation. We then made the hypothesis that the perception of vestibular-sensed motion duration is embedded within encoding of motion kinetics. The ability to estimate time during passive self-motion in darkness was examined with a self-rotation reproduction paradigm. Subjects were required to replicate through self-driven transport the plateau velocity (30, 60 and 90 degrees /s) and duration (2, 3 and 4s) of the previously imposed whole-body rotation (trapezoid velocity profile) in complete darkness; the rotating chair position was recorded (500 Hz) during the whole trials. The results showed that the peak velocity, but not duration, of the plateau phase of the imposed rotation was accurately reproduced. Suspecting that the velocity instruction had impaired the duration reproduction, we added a control experiment requiring subjects to reproduce two successive identical rotations separated by a momentary motion interruption (MMI). The MMI was of identical duration to the previous plateau phase. MMI duration was fidelitously reproduced whereas that of the plateau phase was hypometric (i.e. lesser reproduced duration than plateau) suggesting that subjective time is shorter during vestibular stimulation. Furthermore, the accurate reproduction of the whole motion duration, that was not required, indicates an automatic process and confirms that vestibular duration perception is embedded within motion kinetics.

Adult↗
PubMed2005

From brainstem to cortex: computational models of saccade generation circuitry.

The brain circuitry of saccadic eye movements, from brainstem to cortex, has been extensively studied during the last 30 years. The wealth of data gathered allowed the conception of numerous computational models. These models proposed descriptions of the putative mechanisms generating this data, and, in turn, made predictions and helped to plan new experiments. In this article, we review the computational models of the five main brain regions involved in saccade generation: reticular formation saccadic burst generators, superior colliculus, cerebellum, basal ganglia and premotor cortical areas. We present the various topics these models are concerned with: location of the feedback loop, multimodal saccades, long-term adaptation, on the fly trajectory correction, strategy and metrics selection, short-term spatial memory, transformations between retinocentric and craniocentric reference frames, sequence learning, to name the principle ones. Our objective is to provide a global view of the whole system. Indeed, narrowing too much the modelled areas while trying to explain too much data is a recurrent problem that should be avoided. Moreover, beyond the multiple research topics remaining to be solved locally, questions regarding the operation of the whole structure can now be addressed by building on the existing models.

Animals↗
PubMed2004

Velocity and curvature in human locomotion along complex curved paths: a comparison with hand movements.

There is extensive experimental evidence linking instantaneous velocity to curvature in drawing and hand-writing movements. The empirical relationship between these characteristics of motion and path is well described by a power law in which the velocity varies in proportion to the one-third power of the radius of curvature. It was recently shown that a similar relationship can be observed during locomotion along curved elliptical paths raising the possibility that these very different motor activities might, at some level, share the same planning strategies. It has, however, been noted that the ellipse is a special case with respect to the one-third power law and therefore these previous results might not provide strong evidence that the one-third power law is a general feature of locomotion around curved paths. For this reason the experimental study of locomotion and its comparison with hand writing is extended here to non-elliptical paths. Subjects walked along predefined curved paths consisting of two complex shapes drawn on the ground: the cloverleaf and the limacon. It was found that the data always supported a close relationship between instantaneous velocity and curvature. For these more complex paths, however, the relationship is shape-dependent--although velocity and curvature can still be linked by a power law, the exponent depends on the geometrical form of the path. The results demonstrate the existence of a close relationship between instantaneous velocity and curvature in locomotion that is more general than the one-third power law. The origins of this relationship and its possible explanation in the mechanical balance of forces and in central planning are discussed.

Adult↗
PubMed2003

Visuo-vestibular interaction in the reconstruction of travelled trajectories.

We recently published a study of the reconstruction of passively travelled trajectories from optic flow. Perception was prone to illusions in a number of conditions, and was not always veridical in the others. Part of the illusionary reconstructed trajectories could be explained by assuming that subjects base their reconstruction on the ego-motion percept built during the stimulus' initial moments. In the current paper, we test this hypothesis using a novel paradigm: if the final reconstruction is governed by the initial percept, providing additional, extra-retinal information that modifies the initial percept should predictably alter the final reconstruction. The extra-retinal stimulus was tuned to supplement the information that was under-represented or ambiguous in the optic flow; the subjects were physically displaced or rotated at the onset of the visual stimulus. A highly asymmetric velocity profile (high acceleration, very low deceleration) was used. Subjects were required to guide an input device (in the form of a model vehicle; we measured position and orientation) along the perceived trajectory. We show for the first time that a vestibular stimulus of short duration can influence the perception of a much longer-lasting visual stimulus. Perception of the ego-motion translation component in the visual stimulus was improved by a linear physical displacement, perception of the ego-motion rotation component by a physical rotation. This led to a more veridical reconstruction in some conditions, but to a less veridical reconstruction in other conditions.

Acceleration↗
PubMed2003

Perception and reproduction of force direction in the horizontal plane.

In this study, we evaluated the capacity of human beings to perceive and reproduce forces applied to the hand. We tested for perceptive distortions and/or privileged directions in the performance of these two tasks. Subjects resisted a reference force applied by a joystick in a given direction, with instructions to keep the hand at a constant position. In a perception task, subjects subsequently resisted a second such force, the direction of which they could adjust with a potentiometer; the task was to reorient the second force to be in the same perceived direction as the reference. In a reproduction task, subjects were instructed to push against the now elastically constrained joystick with the same force that was required to resist the initially applied reference force. Twenty-four reference force directions in the horizontal plane were tested twice each. We observed systematic distortions in the reproduction of force direction that were not present in the perception task. We further observed that the distortions could be predicted by anisotropy of limb stiffness and could be affected by manipulating the mechanical impedance of the hand-joystick interaction. We conclude that human subjects specify and store forces to be applied by the hand not in terms of a perceived force vector, but rather in terms of the motor activity required to resist or produce the force-i.e., subjects possess a multi-dimensional "sense of effort."

Adult↗
PubMed2003

Antisaccade deficit after anterior cingulate cortex resection.

Suppression of unwanted reflexive saccades is a crucial process allowing to sustain voluntary fixation, when required. This inhibition process, which is mainly controlled by the dorsolateral prefrontal cortex, may also involve other cortical and subcortical structures. We prospectively studied the effect of frontal cortical resections involving adjacent regions to the anterior cingulate cortex on the ability to inhibit reflexive saccades. This lesion study included six patients undergoing resection of frontal low grade gliomas, studied prior and after surgery with electro-oculography, using the antisaccade paradigm. Lesions were normalized and mapped in Talairach space allowing to detail the structures whose lesions were associated with antisaccade deficits. In three of the six patients significant early post-operative antisaccade errors were associated with resection of a common critical region, mainly involving the posterior part of the anterior cingulate cortex. This same region was spared in the three remaining patients with no antisaccade deficit, suggesting that the anterior cingulate cortex, known as the cingulate eye field, could play a role in suppression of unwanted saccades.

Adult↗
PubMed2002

Differential effects of labyrinthine dysfunction on distance and direction during blindfolded walking of a triangular path.

While we walk through the environment, we constantly receive inputs from different sensory systems. For us to accomplish a given task, for example to reach a target location, the sensory information has to be integrated to update our knowledge of self-position and self-orientation with respect to the target so that we can correctly plan and perform the remaining trajectory. As has been shown previously, vestibular information plays a minor role in the performance of linear goal-directed locomotion when walking blindfolded toward a previously seen target within a few meters. The present study extends the question of whether vestibular information is a requirement for goal-directed locomotion by studying a more complex task that also involves rotation: walking a triangular path. Furthermore, studying this task provides information about how we walk a given trajectory, how we move around corners, and whether we are able to return to the starting point. Seven young male, five labyrinthine-defective (LD) and five age- and gender-matched control subjects were asked to walk a previously seen triangular path, which was marked on the ground, first without vision (EC) and then with vision (EO). Each subject performed three clockwise (CW) and three counterclockwise (CCW) walks under the EC condition and one CW and CCW walk under the EO condition. The movement of the subjects was recorded by means of a 3D motion analysis system. Analysis of the data showed that LD subjects had, in the EC condition, a significantly larger final arrival error, which was due to increased directional errors during the turns. However, there was no difference between the groups as regards the overall path length walked. This shows that LD subjects were able to plan and execute the given trajectory without vision, but failed to turn correctly around the corners. Hence, the results demonstrate that vestibular information enhances the ability to perform a planned trajectory incorporating whole body rotations when no visual feedback is available.

Adolescent↗
PubMed2002

Multisensory integration for spatial orientation in trait anxiety subjects: absence of visual dependence.

Studies suggest a greater reliance on visual information for maintaining balance in anxious subjects. Nevertheless, links between this supposed preferred visual processing and spatial orientation have not yet been evaluated. Two groups of subjects differing in their level of trait anxiety were formed. Equipped with a head-mounted visual display, they learned a virtual corridor using passive translation but active rotation, both with normal and with two different conflicting sensory conditions. After two visual navigation trials in the corridor, they were blindfolded and asked to reproduce the same trajectory from memory. In addition, subjects drew a map of the remembered corridor. Anxious subjects were comparable to non-anxious subjects when asked to reproduce the trajectory from memory, but exhibited a deficit when drawing a map of the corridor they were in. The results do not support the hypothesis that anxious subjects use preferentially one type of sensory cue over another for spatial orientation, but instead manifest difficulties in constructing more global representations of space.

Adult↗
PubMed2001

Balance control and posture in anxious mice improved by SSRI treatment.

A task requiring dynamic postural stabilisation during locomotion in a conflicting visual vestibular environment (rotating beam), has been devised to assess anxiety-related balance impairments and postural changes in mice. The model, already validated with acutely administered diazepam, was used to assess the action of two chronically administered selective serotonin reuptake inhibitors (SSRIs), fluoxetine and paroxetine. On three behavioural measures (imbalance, elevation of trunk and angle of tail), observed in anxious BALB/cByJ mice, both compounds had the same diazepam-like effects: reduction in number of imbalances, higher elevation of trunk and increase in tail angle. These data suggest, for the first time, that SSRIs should be useful in the treatment of anxiety-induced balance impairments.

Animals↗
PubMed2001

Background, but not foreground, spatial cues are taken as references for head direction responses by rat anterodorsal thalamus neurons.

Two populations of limbic neurons are likely neurophysiological substrates for cognitive operations required for spatial orientation and navigation: hippocampal pyramidal cells discharge selectively when the animal is in a certain place (the "firing field") in the environment, whereas head direction cells discharge when the animal orients its head in a specific, "preferred" direction. Cressant et al. (1997) showed that the firing fields of hippocampal place cells reorient relative to a group of three-dimensional objects only if these are at the periphery, but not the center of an enclosed platform. To test for corresponding responses in head direction cells, three objects were equally spaced along the periphery of a circular platform. Preferred directions were measured before and after the group of objects was rotated. (The rat was disoriented in total darkness between sessions). This was repeated in the presence or absence of a cylinder enclosing the platform. When the enclosure was present, the preferred directions of all 30 cells recorded shifted by the same angle as the objects. In the absence of the enclosure, the preferred directions did not follow the objects, remaining fixed relative to the room. These results provide a possible neurophysiological basis for observations from psychophysical experiments in humans that background, rather than foreground, cues are preferentially used for spatial orientation.

Animals↗
PubMed2001

Relationship between velocity and curvature of a human locomotor trajectory.

Human locomotion involves the coordination of the movements of the limbs to allow the subject to navigate in the environment. Here we study some curved locomotor paths with the hypothesis that, also during locomotion, movement obey the so-called 'two-thirds power law' stating that the angular velocity of the end effector (here the entire body) is proportional to the two-thirds root of its curvature. We recorded the path of subjects who had to reproduce by mean of displacements of their entire body some circular or elliptical shapes drawn on the ground. Our results clearly show that human subjects adapt their locomotor velocity to the radius of curvature of the path they are following in accordance with the prediction of the power law. These results suggest that for the locomotor system, the central nervous system computes motor strategies in 2D navigational space by taking into account the shape of the path to be followed.

Biomechanical Phenomena↗
PubMed2001

Impairment of predictive saccades in schizophrenia.

Using infrared oculography, we compared saccades toward predictable and pseudo-random visual targets in 19 neuroleptic-free patients with schizophrenia (including 13 neuroleptic-naïve patients) and in 29 age- and gender-matched healthy volunteers. Externally driven saccades were not different between patients and controls, whether or not the target was predictable. Anticipated saccades were specifically less accurate in the patients compared to the controls. The difference between primary gain of anticipated and non-anticipated saccades was markedly higher in the patients compared to controls (p=0.003). These results point to a deficit in the early step of internally driven oculomotor planning in schizophrenia.

Adult↗
PubMed2001

Predictive elements in ocular interception and tracking of a moving target by untrained cats.

We presented a mechanical target moving at constant velocity to awake, nontrained, head-restrained cats, in order to study how naive animals pursue objects moving at a high speed with their gaze. Eye movements were recorded while the target was moving in different directions at a constant velocity (20-80 degrees/s) through the center of the visual field. We observed two oculomotor strategies: cats either made an interception saccade (IS) toward the target but opposite to its motion, or tracked it in the direction of motion. They used the interception strategy more frequently when the gaze position error at the onset of target motion was large, and the tracking strategy when it was small. Interception was always achieved by single saccades, which were faster than tracking saccades (TS). During tracking, cats generated sequences of two to six saccades separated by "smooth" eye movements. Tracking quality varied considerably from trial to trial. When the level of motivation was high, cats would track the target at 80 degrees/s over up to 75% of the oculomotor range, with relatively small position errors. We compared ISs and TSs with respect to their metric properties and timing. The amplitudes of ISs positively correlated with position error existing 100 ms before saccade onset, but saccade vectors were directed to a point ahead of the target along the target's track. We conclude that, in programming the ISs, target motion is used to predict the future target position so as to assure a spatial lead of the gaze at the saccade end, instead of attempting a precise capture of the target. The amplitude of TSs did not depend on preceding position errors. TSs were usually small at the onset of the first saccade, as if cats would wait till the target arrived near the line of sight. A majority of primary TSs were initiated before the target arrived near the direction of gaze. Thus they had a direction, opposite to the position error sampled 100 ms before the saccade, but the same as the direction of target motion. Prediction of the future target position from its velocity vector should therefore contribute to the programming of TSs. In addition, we observed that TSs were faster when they were initiated with a spatial lag relative to the target and they were slower if there was a spatial lead or target velocity was reduced. Such a modulation appears to be analogous to the predictive correction of the saccade amplitude during smooth pursuit in primates. Considering strong visual motion sensitivity and motor properties of output neurons of the superior colliculus, it is likely that, in cats, the colliculus makes a major contribution to the integration of eye movement-related and target motion-related signals.

Animals↗
PubMed2001

Active, passive and snapshot exploration in a virtual environment: influence on scene memory, reorientation and path memory.

We investigated the importance of active, passive and snapshot exploration on spatial memory in a virtual city. The exploration consisted in traveling along a series of streets. 'Active exploration' was performed by giving directions to the subject who controlled his displacement with a joystick. During 'passive' exploration, the travel was imposed by the computer. Finally, during 'snapshot exploration', simple views of the scene were presented sequentially every 4 m. Travel velocity was the same in all cases. The three visual exploration modes were compared with three spatial memory measures: (1) scene recognition, (2) at the end of the path, reorientation toward the departure point and (3) drawings of the path shape. Scene recognition and estimation of the direction of the starting point of the path were not affected by the mode of exploration. In contrast, reproduction of the shape of the path was affected: the errors of reproduction were greater for the snapshot exploration than for the other two conditions; there was no difference between the other two conditions. These results suggest that (1) 2D image features from a visual scene are memorized. Moreover, (2) pointing towards the origin of the path relies on motion duration integration or a frame of reference integrated during displacement. Finally, (3) drawing the path shape involves a deliberate reconstruction process.

Adult↗
PubMed2001

Mental imagery of visual motion modifies the perception of roll-vection stimulation.

When viewing a wide-angle visual display, which rotates in the frontoparallel plane around the line of sight, observers experience an illusory shift of the direction of gravity; this shift leads to an apparent tilt of the body and displaces allocentric space coordinates. In this study, subjects adjusted an indicator to the apparent horizontal while viewing a rotating display. To determine whether top down processes could affect the illusion, the subjects were asked to visualize a rotating configuration of dots onto a blank central portion of the moving visual field. Visualizing dots and actually viewing the dots deflected the spatial judgment in very similar ways. These results demonstrate that top down processing can affect allocentric space coordinates.

Adolescent↗