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A Berthoz

Publications and source records attributed to A Berthoz.

At least 37 records · Page 2Linked to original sources
PubMed2001

Human cortical networks for new and familiar sequences of saccades.

Visual exploration is organized in sequences of saccadic eye movements that depend on both perceptual and cognitive context. Using functional magnetic resonance imaging, we studied the neural basis of sequential oculomotor behavior and its dependence on different types of memory by analyzing cerebral activity during performance of newly learned and familiar sequences of eye movements. Compared to a resting condition, both types of sequences activated a common fronto-parietal network, including frontal and supplementary eye fields, and several parietal areas. Within this network, newly learned sequences induced stronger activation than familiar sequences, probably reflecting higher attentional demands. In addition, specific regions were recruited for the performance of new sequences, including pre-supplementary eye fields, the precuneus and the caudate nucleus. This indicates that in addition to attentional modulation, novelty of saccadic sequences requires specific cortical resources, probably related to effortful sequence preparation and coordination as well as to spatial working memory. For familiar sequences, recalled from long-term memory, we observed specific right medial temporo-occipital activation in the vicinity of the boundary between the parahippocampal and lingual gyri, as well as an activation site in the parieto-occipital fissure. We conclude that neuronal resources recruited by the gaze system can change with the familiarity of the scanpath to be executed. This study is important to better understand how the brain implements memorized scanpaths for visual exploration and orienting.

Adult↗
PubMed2001

Active locomotion increases peak firing rates of anterodorsal thalamic head direction cells.

Head direction (HD) cells discharge selectively in macaques, rats, and mice when they orient their head in a specific ("preferred") direction. Preferred directions are influenced by visual cues as well as idiothetic self-motion cues derived from vestibular, proprioceptive, motor efferent copy, and command signals. To distinguish the relative importance of active locomotor signals, we compared HD cell response properties in 49 anterodorsal thalamic HD cells of six male Long-Evans rats during active displacements in a foraging task as well as during passive rotations. Since thalamic HD cells typically stop firing if the animals are tightly restrained, the rats were trained to remain immobile while drinking water distributed at intervals from a small reservoir at the center of a rotatable platform. The platform was rotated in a clockwise/counterclockwise oscillation to record directional responses in the stationary animals while the surrounding environmental cues remained stable. The peak rate of directional firing decreased by 27% on average during passive rotations (r(2) = 0.73, P < 0.001). Individual cells recorded in sequential sessions (n = 8) reliably showed comparable reductions in peak firing, but simultaneously recorded cells did not necessarily produce identical responses. All of the HD cells maintained the same preferred directions during passive rotations. These results are consistent with the hypothesis that the level of locomotor activity provides a state-dependent modulation of the response magnitude of AD HD cells. This could result from diffusely projecting neuromodulatory systems associated with motor state.

Action Potentials↗
PubMed2001

Role of lateral acceleration in curve driving: driver model and experiments on a real vehicle and a driving simulator.

Experimental studies show that automobile drivers adjust their speed in curves so that maximum vehicle lateral accelerations decrease at high speeds. This pattern of lateral accelerations is described by a new driver model, assuming drivers control a variable safety margin of perceived lateral acceleration according to their anticipated steering deviations. Compared with a minimum time-to-lane-crossing (H. Godthelp, 1986) speed modulation strategy, this model, based on nonvisual cues, predicts that extreme values of lateral acceleration in curves decrease quadratically with speed, in accordance with experimental data obtained in a vehicle driven on a test track and in a motion-based driving simulator. Variations of model parameters can characterize "normal" or "fast" driving styles on the test track. On the simulator, it was found that the upper limits of lateral acceleration decreased less steeply when the motion cuing system was deactivated, although drivers maintained a consistent driving style. This is interpreted per the model as an underestimation of curvilinear speed due to the lack of inertial stimuli. Actual or potential applications of this research include a method to assess driving simulators as well as to identify driving styles for on-board driver aid systems.

Acceleration↗
PubMed2001

Localization of human frontal eye fields: anatomical and functional findings of functional magnetic resonance imaging and intracerebral electrical stimulation.

OBJECT: The goal of this study was to investigate the anatomical localization and functional role of human frontal eye fields (FEFs) by comparing findings from two independently conducted studies. METHODS: In the first study, 3-tesla functional magnetic resonance (fMR) imaging was performed in 14 healthy volunteers divided into two groups: the first group executed self-paced voluntary saccades in complete darkness and the second group repeated newly learned or familiar sequences of saccades. In the second study, intracerebral electrical stimulation (IES) was performed in 38 patients with epilepsy prior to surgery, and frontal regions where stimulation induced versive eye movements were identified. These studies showed that two distinct oculomotor areas (OMAs) could be individualized in the region classically corresponding to the FEFs. One OMA was consistently located at the intersection of the superior frontal sulcus with the fundus of the superior portion of the precentral sulcus, and was the OMA in which saccadic eye movements could be the most easily elicited by electrical stimulation. The second OMA was located more laterally, close to the surface of the precentral gyrus. The fMR imaging study and the IES study demonstrated anatomical and stereotactic agreement in the identification of these cortical areas. CONCLUSIONS: These findings indicate that infracentimetric localization of cortical areas can be achieved by measuring the vascular signal with the aid of 3-tesla fMR imaging and that neuroimaging and electrophysiological recording can be used together to obtain a better understanding of the human cortical functional anatomy.

Adult↗
PubMed2001

[Neural basis of spatial orientation and memory of routes: topokinetic memory or topokinesthesic memory].

The neural basis of spatial orientation and the memory of routes have been explored by brain imaging (PET SCAN and fMRI) in human. Several cognitive strategies and several types of reference frames can be used by the brain to establish relations between our body and the environment. Four categories of brain areas have been considered: the areas involved in egocentric and allocentric coding on one hand and on the other hand the areas involved in the "route" like and the "survey or map" like strategies used during tasks in which subjects had to mentally remember a path by mental navigation or mental scanning of a map. The results have confirmed that parietal and frontal structures involved in "spatial neglect" are also found to be involved in the egocentric orientation tasks of subjective midline detection. More generally we have been able to identify parieto-frontal areas involved in visuo-spatial memory. In addition we have identified the areas involved in the cortical processing of vestibular information and lastly we have shown that in addition to the parieto-frontal areas a parieto temporal lobe network is involved in allocentric tasks and also during mental navigation by route or survey strategies. These results contribute to the identification of the neural basis of topographic memory but they also suggest that we have to define a particular type of spatial memory which is involved in the memory of routes and movements which we suggest to call "topo-kinetic" or "topo-kinesthetic" memory.

Brain Mapping↗
PubMed2000

Balance control and posture differences in the anxious BALB/cByJ mice compared to the non anxious C57BL/6J mice.

A relation between anxiety disorders and balance control dysfunctions has been observed in many studies in humans. A mismatch in the integration of sensory inputs could trigger these disturbances. Very few experimental animal procedures have been designed to study the functional link between anxiety and balance control. A task was therefore developed, challenging the visual, vestibular and somesthesic sensory systems in mice. The test, called the 'rotating beam', gave an accurate assessment of balance control and the posture, using sensitive measures (number of falls and imbalances, position of tail and trunk). Striking differences were observed between the two inbred strains of mice known to have radically different anxiety-related behaviour. The highly anxious strain, BALB/cByJ, performed poorly compared to the non anxious strain, C57BL/6J. Balance control and postural abilities of anxious mice were improved by acute anxiolytic diazepam treatment. Lower behavioural performance level was registered in non anxious mice given anxiogenic beta-CCM treatment. The findings account for a strong relationship between anxiety and balance control in mice. Finally, the highly sensitive procedure proved to be well suited to the study of functional links between anxiety and sensorimotor processes.

Animals↗
PubMed2000

Lack of anticipatory gaze-orienting responses in patients with right brain damage.

OBJECTIVE: To study eye movements during cervical proprioceptive stimulation by passive body rotation in darkness, with the head held stationary, in patients with right brain damage and hemineglect. BACKGROUND: At very low frequency, this stimulation is reported to produce an illusion of head turning in space and eye deviations directed opposite to trunk rotation (in the direction of the illusory head rotation). METHODS: Ten normal subjects and seven patients with unilateral cerebral lesions (five right brain-damaged patients with mild to moderate visuospatial neglect, two left brain-damaged patients without neglect) were included in the study. Subjects were seated on a rotating chair. Stimuli consisted of slow sinusoidal passive trunk rotations (+/-30 degrees, 0.01 Hz) while the head was fixed in space. RESULTS: Eye movements directed opposite to trunk rotation were typical for normal subjects and for left brain-damaged patients. In contrast, all right brain-damaged patients showed either eye movements in the direction of trunk rotation or no eye deviations at all. CONCLUSION: This result could characterize a lack of anticipatory coordinating gaze behavior in patients with right brain damage.

Aged↗
PubMed2000

Spatial, not temporal cues drive predictive orienting movements during navigation: a virtual reality study.

A fundamental property of the human brain is the ability to make predictions of future sensory and motor events. We have recently found that steering manoeuvres when walking along curvilinear trajectories are controlled by an anticipatory guidance of the direction of head (and eyes). However it is unclear whether a time-related or space-related signal triggers such anticipatory head orienting movements. By simulating navigation along a multi-legged virtual corridor we show that anticipatory orienting movements are triggered (in standing subjects) by reaching specific locations rather than by the time to the approaching corridor's bend. Similar to what happens in car driving, specific spatial features of the route rather than time to collision seem to drive steering.

Adult↗
PubMed2000

Eye deviation during rotation in darkness in trait anxiety: an early expression of perceptual avoidance?

BACKGROUND: Patients with dizziness and patients with panic disorder and agoraphobia share a common symptomatology. Numerous studies have investigated a potential link between anxiety and the vestibular system, but few of them have addressed the specific topic of spatial representation. METHODS: Passive whole-body rotations in the horizontal plane were imposed on two groups of subjects who differed in their level of trait anxiety. Subjects were seated on a mobile robot in darkness. After each passive rotation, subjects were asked to reproduce the stimulus by driving the robot with a joystick and to perform a rotation of the same magnitude. Eye movements were recorded and analyzed. RESULTS: No difference in either perception (accuracy in the reproduction task) or in VOR gain was found between the two groups of subjects. Mean eye deviation, caused by fast phases of the nystagmus, differed in the two groups. It was typically in the anticompensatory direction in the non-anxious group, and in the compensatory direction the anxious group. Such compensatory movement may be explained by an egocentric orientation strategy, that may in turn indicate a lack of interest toward the visual surroundings. CONCLUSIONS: An egocentric strategy for self-orientation exhibited at a level below the threshold of awareness could reveal the existence of a physiological mode of processing leading to agoraphobic avoidance.

Adult↗
PubMed2000

Neural correlates of topographic mental exploration: the impact of route versus survey perspective learning.

There are two major sources of information to build a topographic representation of an environment, namely actual navigation within the environment (route perspective) and map learning (survey perspective). The aim of the present work was to use positron emission tomography (PET) to compare the neural substrate of the topographic representation built from these two modes. One group of subjects performed a mental exploration task in an environment learned from actual navigation (mental navigation task). Another group of subjects performed exploration in the same environment learned from a map (mental map task). A right hippocampal activation common to both mental navigation and mental map tasks was evidenced and may correspond the neural substrate of a "dual-perspective" representation. The parahippocampal gyrus was additionally activated bilaterally during mental navigation only. These results suggest that the right hippocampus involvement would be sufficient when the representation incorporates essentially survey information while the bilateral parahippocampal gyrus would be involved when the environment incorporates route information and includes "object" landmarks. The activation of a parietofrontal network composed of the intraparietal sulcus, the superior frontal sulcus, the middle frontal gyrus, and the pre-SMA was observed in common for both mental navigation and mental map and is likely to reflect the spatial mental imagery components of the tasks.

Adult↗
PubMed2000

The neural basis of egocentric and allocentric coding of space in humans: a functional magnetic resonance study.

The spatial location of an object can be represented in the brain with respect to different classes of reference frames, either relative to or independent of the subject's position. We used functional magnetic resonance imaging to identify regions of the healthy human brain subserving mainly egocentric or allocentric (object-based) coordinates by asking subjects to judge the location of a visual stimulus with respect to either their body or an object. A color-judgement task, matched for stimuli, difficulty, motor and oculomotor responses, was used as a control. We identified a bilateral, though mainly right-hemisphere based, fronto-parietal network involved in egocentric processing. A subset of these regions, including a much less extensive unilateral, right fronto-parietal network, was found to be active during object-based processing. The right-hemisphere lateralization and the partial superposition of the egocentric and the object-based networks is discussed in the light of neuropsychological findings in brain-damaged patients with unilateral spatial neglect and of neurophysiological studies in the monkey.

Adult↗
PubMed2000

Self-motion perception during a sequence of whole-body rotations in darkeness.

The main aim of this study was to examine how postrotatory effects, induced by passive whole-body rotations in darkness, could alter the perception of motion and eye movements during a subsequent rotation. Perception of angle magnitude was assessed in a reproduction task: blindfolded subjects were first submitted to a passive rotation about the earth-vertical axis on a mobile robot. They were then asked to reproduce this angle by controlling the robot with a joystick. Stimulus rotations ranged from 80 degrees to 340 degrees. Subjects were given one of two delay instructions: after the stimulus, they either had to await the end of postrotatory sensations before starting reproduction (condition free delay, FD), or they had to start immediately after the end of the stimulus rotation (no delay, ND). The delay in FD was used as an incidental measure of the subjective duration of these sensations. Eye movements were recorded with an infrared measuring system (IRIS). Results showed that in both conditions subjects accurately reproduced rotation angles, though they did not reproduce the stimulus dynamics. Peak velocities reached in ND were higher than in FD. This difference suggests that postrotatory effects induced a bias in the perception of angular velocity in the ND condition.

Acceleration↗
PubMed2000

Mental rotation for spatial environment recognition.

We investigated the importance of retinal and body inclination in the recognition of spatial environment. The paradigm involved the recognition, in body upright and tilted conditions, of tilted images -intervals of 15 degrees from 0 degrees to 90 degrees leftward and rightward respective to head coordinates - of known spatial layouts encountered while walking in Paris. The analysis of reaction times was consistent with the subjects mentally rotating the spatial layout so that the environment was subjectively vertical before making their decisions. In contrast, when the body was roll-tilted (33 degrees ), overall reaction time was not affected; however, reaction time and spatial layout tilt with respect to the head were correlated when the body was tilted but not when upright. Both results indicate that gravity was slightly important in performing the task.

Adult↗
PubMed2000

Visual perception of motion and 3-D structure from motion: an fMRI study.

Functional magnetic resonance imaging was used to study the cortical bases of 3-D structure perception from visual motion in human. Nine subjects underwent three experiments designed to locate the areas involved in (i) motion processing (random motion versus static dots), (ii) coherent motion processing (expansion/ contraction versus random motion) and (iii) 3-D shape from motion reconstruction (3-D surface oscillating in depth versus random motion). Two control experiments tested the specific influence of speed distribution and surface curvature on the activation results. All stimuli consisted of random dots so that motion parallax was the only cue available for 3-D shape perception. As expected, random motion compared with static dots induced strong activity in areas V1/V2, V5+ and the superior occipital gyrus (SOG; presumptive V3/V3A). V1/V2 and V5+ showed no activity increase when comparing coherent motion (expansion or 3-D surface) with random motion. Conversely, V3/V3A and the dorsal parieto-occipital junction were highlighted in both comparisons and showed gradually increased activity for random motion, coherent motion and a curved surface rotating in depth, which suggests their involvement in the coding of 3-D shape from motion. Also, the ventral aspect of the left occipito-temporal junction was found to be equally responsive to random and coherent motion stimuli, but showed a specific sensitivity to curved 3-D surfaces compared with plane surfaces. As this region is already known to be involved in the coding of static object shape, our results suggest that it might integrate various cues for the perception of 3-D shape.

Adult↗
PubMed2000

Modulation of spatial orientation processing by mental imagery instructions: a MEG study of representational momentum.

Under appropriate conditions, an observer's memory for the final position of an abruptly halted moving object is distorted in the direction of the represented motion. This phenomenon is called "representational momentum" (RM). We examined the effect of mental imagery instructions on the modulation of spatial orientation processing by testing for RM under conditions of picture versus body rotation perception and imagination. Behavioral data were gathered via classical reaction time and error measurements, whereas brain activity was recorded with the help of magnetoencephalography (MEG). Due to the so-called inverse problem and to signal complexity, results were described at the signal level rather than with the source location modeling. Brain magnetic field strength and spatial distribution, as well as latency of P200m evoked fields were used as neurocognitive markers. A task was devised where a subject examined a rotating sea horizon as seen from a virtual boat in order to extrapolate either the picture motion or the body motion relative to the picture while the latter disappeared temporarily until a test-view was displayed as a final orientation candidate. Results suggest that perceptual interpretation and extrapolation of visual motion in the roll plane capitalize on the fronto-parietal cortical networks involving working memory processes. Extrapolation of the rotational dynamics of sea horizon revealed a RM effect simulating the role of gravity in rotational equilibrium. Modulation of the P200m component reflected spatial orientation processing and a non-voluntary detection of an incongruity between displayed and expected final orientations given the implied motion. Neuromagnetic properties of anticipatory (Contingent Magnetic Variation) and evoked (P200m) brain magnetic fields suggest, respectively, differential allocation of attentional resources by mental imagery instructions (picture vs. body tilt), and a communality of neural structures (in the right centro-parietal region) for the control of both RM and mental rotation processes. Finally, the RM of the body motion is less prone to forward shifts than that of picture motion evidencing an internalization of the implied mass of the virtual body of the observer.

Adult↗
PubMed2000

A common mechanism for the control of eye and head movements in humans.

How the human brain controls the subtle coupling between eye and head movements is still debated. The brain could either coordinate two separate (eye and head) networks or use a single system involved in gaze (eye + head) control. In a recent report, a total transfer from eye to head movements was observed in a patient with congenital ophthalmoplegia. This led the authors to hypothesize that such transfer resulted from a long-term adaptation between oculomotor and head movement systems. We report on a patient in whom a similar transfer was observed but at the acute stage of an acquired ophthalmoplegia. This case demonstrates that the transfer between head and eye movements does not necessarily require long-term adaptation and supports the hypothesis of a common unique gaze motor command in which eye and head movements would be rapidly exchangeable.

Adult↗
PubMed1999

Visual mental imagery interferes with allocentric orientation judgements.

The subjective visual vertical is determined when a subject judges the orientation of an indicator (e.g. a short line segment) as apparently vertical. The mechanisms that underlie this perceptual performance are usually assumed to be based predominantly on bottom-up processing of primarily vestibular and visual information. However, it is also possible that top-down processes play a role in such abilities. We used an interference paradigm in order to investigate the effects of mental images on the perception of the visual vertical. The results demonstrate for the first time that visual mental imagery can exert the same directional influence on the subjective visual vertical as a perception of the corresponding stimulus.

Adolescent↗