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This study assessed the impact of sex and typical aging on visuospatial working memory (VSWM), mental rotations, and navigational strategies using behavioral information. Fifty healthy participants regrouped in older (OA) and young adults (YA) performed the Walking Corsi test (WalCT) and the Redrawn Mental Rotation Test (MRT) to explore mental rotation abilities. We recorded kinematic data such as locomotion trajectories, and spatial orientations during navigation. We created a new method of data analysis for the WalCT performances and compared it with the classical approach. This original method allowed us to identify cognitive strategies based on errors analysis. Our data suggested that VSWM and mental rotation capacities in locomotion were modulated by age (YA scored higher than OA), and sex (Young Adult Males (YA-M) having higher performance than Young Adult Females (YA-F). We observed a preferential use of cognitive strategies related to sex; YA-F relied more on egocentric strategies whereas YA-M relied more on allocentric strategies. The preferential use of cognitive strategies in the YA group was not observed in the OA group producing more random errors per sequence. The results suggest the effects that age and sex have on VSWM, cognitive strategies, and mental rotation during navigation and highlight the importance of navigational strategies training.

Interactions between two brains constitute the essence of social communication. Daily movements are commonly executed during social interactions and are determined by different mental states that may express different positive or negative behavioral intent. In this context, the effective recognition of festive or violent intent before the action execution remains crucial for survival. Here, we hypothesize that the EEG signals contain the distinctive features characterizing movement intent already expressed before movement execution and that such distinctive information can be identified by state-of-the-art classification algorithms based on Riemannian geometry. We demonstrated for the first time that a classifier based on covariance matrices and Riemannian geometry can effectively discriminate between neutral, festive, and violent mental states only on the basis of non-invasive EEG signals in both the actor and observer participants. These results pave the way for new electrophysiological discrimination of mental states based on non-invasive EEG recordings and cutting-edge machine learning techniques., info:eu-repo/semantics/published

In the original publication of the article.

International audience; Spatial memory and navigation capabilities tend to decline in normal aging, but few studies have assessed the impact of landmarks on route learning in a large-scale environment. The objectives were to examine age-related effects on visuo-spatial working memory capabilities in various environments and to determine the impact of landmarks in navigation skills in normal aging. 42 young women (23.6 ± 4.9 years) and 37 older women (70.7 ± 4.7 years) with no cognitive impairment have performed three visuo-spatial working memory tests: one in reaching space (computerized Corsi-Block-Tapping test) and two in locomotor navigation space (a condition without landmarks: Virtual Walking Corsi Test and a condition with landmarks: Virtual Room Walking Test). A two-way mixed ANOVA test showed that the young subjects performed better in all conditions than older subjects. The performance in visuo-spatial working memory thus decreases with age. Visuo-spatial working memory performances were identical in reaching and navigation spaces for both groups. The integration of landmarks into a navigational task decreases performance in older women, while this performance is not altered in younger women.

In the visuospatial domain, perspective taking is the ability to imagine how a visual scene appears from an external observer's viewpoint, and can be studied by asking subjects to encode object locations in a visual scene where another individual is present and then detecting their displacement when seeing the scene from the other's viewpoint. In the current study, we explored the relationship between visuospatial perspective taking and self-report measures of the cognitive and emotional components of empathy in young adults. To this aim, we employed a priming paradigm, in which the presence of an avatar allowed to anticipate the next perceived perspective on the visual scene. We found that the emotional dimension of empathy was positively correlated with the behavioral advantage provided by the presence of the avatar, relative to unprimed perspective changes. These data suggest a link between the tendency to vicariously experience the others' emotions and the ability to perform self-other spatial transformations.

How do we choose a particular action among equally valid alternatives? Nonhuman primate findings have shown that decision-making implicates modulations in unit firing rates and local field potentials (LFPs) across frontal and parietal cortices. Yet the electrophysiological brain mechanisms that underlie free choice in humans remain ill defined. Here, we address this question using rare intracerebral electroencephalography (EEG) recordings in surgical epilepsy patients performing a delayed oculomotor decision task. We find that the temporal dynamics of high-gamma (HG, 60–140 Hz) neural activity in distinct frontal and parietal brain areas robustly discriminate free choice from instructed saccade planning at the level of single trials. Classification analysis was applied to the LFP signals to isolate decision-related activity from sensory and motor planning processes. Compared with instructed saccades, free-choice trials exhibited delayed and longer-lasting HG activity during the delay period. The temporal dynamics of the decision-specific sustained HG activity indexed the unfolding of a deliberation process, rather than memory maintenance. Taken together, these findings provide the first direct electrophysiological evidence in humans for the role of sustained high-frequency neural activation in frontoparietal cortex in mediating the intrinsically driven process of freely choosing among competing behavioral alternatives., How do we choose a particular action among equally valid alternatives? Intracranial recordings in humans performing a delayed oculomotor decision task reveal that deliberating between competing alternatives during free choice is indexed by sustained high frequency neural activity in a network of parieto-frontal brain areas.

Here, we examine how different emotions-happiness, fear, sadness and anger-affect the kinematics of locomotion. We focus on a compact representation of locomotion properties using the intersegmental law of coordination (Borghese et al. in J Physiol 494(3):863-879, 1996), which states that, during the gait cycle of human locomotion, the elevation angles of the thigh, shank and foot do not evolve independently of each other but form a planar pattern of co-variation. This phenomenon is highly robust and has been extensively studied. The orientation of the plane has been correlated with changes in the speed of locomotion and with reduction in energy expenditure as speed increases. An analytical model explaining the conditions underlying the emergence of this plane and predicting its orientation reveals that it suffices to examine the amplitudes of the elevation angles of the different segments along with the phase shifts between them (Barliya et al. in Exp Brain Res 193:371-385, 2009). We thus investigated the influence of different emotions on the parameters directly determining the orientation of the intersegmental plane and on the angular rotation profiles of the leg segments, examining both the effect of changes in walking speed and effects independent of speed. Subjects were professional actors and naïve subjects with no training in acting. As expected, emotions were found to strongly affect the kinematics of locomotion, particularly walking speed. The intersegmental coordination patterns revealed that emotional expression caused additional modifications to the locomotion patterns that could not be explained solely by a change in speed. For all emotions except sadness, the amplitude of thigh elevation angles changed from those in neutral locomotion. The intersegmental plane was also differently oriented, especially during anger. We suggest that, while speed is the dominant variable allowing discrimination between different emotional gaits, emotion can be reliably recognized in locomotion only when speed is considered together with these kinematic changes.

Spatial navigation from memory can rely on two different strategies: a mental simulation of a kinesthetic spatial navigation (egocentric route strategy) or visual-spatial memory using a mental map (allocentric survey strategy). We hypothesized that a previously performed "oculomotor navigation" on a map could be used by the brain to perform a locomotor memory task. Participants were instructed to (1) learn a path on a map through a sequence of vertical and horizontal eyes movements and (2) walk on the slabs of a "magic carpet" to recall this path. The main results showed that the anisotropy of ocular movements (horizontal ones being more efficient than vertical ones) influenced performances of participants when they change direction on the central slab of the magic carpet. These data suggest that, to find their way through locomotor space, subjects mentally repeated their past ocular exploration of the map, and this visuo-motor memory was used as a template for the locomotor performance.

During locomotion, a top-down organization has been previously demonstrated with the head as a stabilized platform and gaze anticipating the horizontal direction of the trajectory. However, the quantitative assessment of the anticipatory sequence from gaze to trajectory and body segments has not been documented. The present paper provides a detailed investigation into the spatial and temporal anticipatory relationships among the direction of gaze and body segments during locomotion. Participants had to walk along several mentally simulated complex trajectories, without any visual cues indicating the trajectory to follow. The trajectory shapes were presented to the participants on a sheet of paper. Our study includes an analysis of the relationships between horizontal gaze anticipatory behavior direction and the upcoming changes in the trajectory. Our findings confirm the following: 1) The hierarchical ordered organization of gaze and body segment orientations during complex trajectories and free locomotion. Gaze direction anticipates the head orientation, and head orientation anticipates reorientation of the other body segments. 2) The influence of the curvature of the trajectory and constraints of the tasks on the temporal and spatial relationships between gaze and the body segments: Increased curvature resulted in increased time and spatial anticipation. 3) A different sequence of gaze movements at inflection points where gaze plans a much later segment of the trajectory.

We studied the influence of vision (walking with or without vision) and of gait direction (walking forward or backward) on goal-oriented locomotion in humans. Subjects had to walk, in a free environment, from a given position and orientation towards a distant arrow which constrained their final position and orientation. We found that the average trajectories were mostly similar across the tested conditions, which suggests that locomotor trajectories are generated at a high cognitive level and, to some extent, independently of the detailed sensory and motor implementation levels. The variability profiles around the average trajectories were similar across the gait direction conditions but differed greatly across the visual conditions, indicating the existence of motor-independent and vision-dependent control mechanisms. Taken together, our observations argue further in favour of a top-down implementation of goal-oriented locomotion, where the control of locomotion is specified at the level of whole-body trajectories and then implemented through specific motor strategies.

Path integration is a fundamental mechanism of spatial navigation. In non-human species, it is assumed to be an online process in which a homing vector is updated continuously during an outward journey. In contrast, human path integration has been conceptualized as a configural process in which travelers store working memory representations of path segments, with the computation of a homing vector only occurring when required. To resolve this apparent discrepancy, we tested whether humans can employ different path integration strategies in the same task. Using a triangle completion paradigm, participants were instructed either to continuously update the start position during locomotion (continuous strategy) or to remember the shape of the outbound path and to calculate home vectors on basis of this representation (configural strategy). While overall homing accuracy was superior in the configural condition, participants were quicker to respond during continuous updating, strongly suggesting that homing vectors were computed online. Corroborating these findings, we observed reliable differences in head orientation during the outbound path: when participants applied the continuous updating strategy, the head deviated significantly from straight ahead in direction of the start place, which can be interpreted as a continuous motor expression of the homing vector. Head orientation-a novel online measure for path integration-can thus inform about the underlying updating mechanism already during locomotion. In addition to demonstrating that humans can employ different cognitive strategies during path integration, our two-systems view helps to resolve recent controversies regarding the role of the medial temporal lobe in human path integration.

Substantial data from the cognitive neurosciences point to the importance of bodily processing for the development of a comprehensive theory of the self. A key aspect of the bodily self is self-location, the experience that the self is localized at a specific position in space within one's bodily borders (embodied self-location). Although the neural mechanisms of self-location have been studied by manipulating the spatial location of one's visual perspective during mental imagery, such experiments were conducted in constrained, explicit, and unecological contexts such as explicit instructions in a prone/seated position, although most human interactions occur spontaneously while standing/walking. Using a motor paradigm, we investigated the behavioral and neural mechanisms of spontaneous self-location and mental body transformations during active human interaction. Using own-body imagery using spontaneous and explicit changes in self-location in standing participants, we report that spontaneous interactions with an avatar are neurally indistinguishable from explicit own-body transformation with disembodied self-location but differ from explicit own-body transformation with embodied self-location at 400–600 ms after stimulus onset. We discuss these findings with respect to the neural mechanisms of perspective-taking and self-location in spontaneous human interaction.

We review human functional neuroimaging studies that have explicitly investigated the reference frames used in different cortical regions for representing spatial locations of objects. Beyond the general distinction between "egocentric" and "allocentric" reference frames, we provide evidence for the selective involvement of the posterior parietal cortex and associated frontal regions in the specific process of egocentric localization of visual and somatosensory stimuli with respect to relevant body parts ("body referencing"). Similarly, parahippocampal and retrosplenial regions, together with specific parietal subregions such as the precuneus, are selectively involved in a specific form of allocentric representation in which object locations are encoded relative to enduring spatial features of a familiar environment ("environmental referencing"). We also present a novel functional magnetic resonance imaging study showing that these regions are selectively activated, whenever a purely perceptual spatial task involves an object which maintains a stable location in space during the whole experiment, irrespective of its perceptual features and its orienting value as a landmark. This effect can be dissociated from the consequences of an explicit memory recall of landmark locations, a process that further engages the retrosplenial cortex.

The posterior parietal cortex is involved in numerous visuospatial tasks, but little is known about the lateralization of these functions. We used functional magnetic resonance imaging to map the posterior parietal areas involved in saccades. Cerebral activation was studied during three different steps of saccadic elaboration: internal Decision of where to direct a horizontal saccade, motor Preparation and saccade Execution. These steps activated distinct areas: Decision and Preparation selectively activated the left posterior parietal cortex (left deep posterior intraparietal sulcus and left medial posterior intraparietal sulcus), whereas Execution activated only the right posterior parietal cortex (right medial posterior intraparietal sulcus). In humans, left but not right posterior parietal cortex might be specifically related to decision making and preparation of forthcoming ocular saccades.

Human locomotion was investigated in a goal-oriented task where subjects had to walk to and through a doorway starting from a fixed position and orientation in space. The door was located at different positions and orientations in space, resulting in a total of 40 targets. While no specific constraint was provided to subjects in terms of the path they were to follow or the expected walking speeds, all of them generated very similar trajectories in terms of both path geometry and velocity profiles. These results are reminiscent of the stereotyped properties of the hand trajectories observed in arm reaching movements in studies over the last 20 years. This observation supports the hypothesis that common constraining mechanisms govern the generation of segmental and whole-body trajectories. In contrast, we observed that the subjects placed their feet at different spatial positions across repetitions, making unlikely the hypothesis that goal-oriented locomotion is planned as a succession of steps. Rather, our results suggest that common planning and/or control strategies underlie the formation of the whole locomotor trajectory during a spatially oriented task.

Despite the theoretically infinite number of possible trajectories a human may take to reach a distant doorway, we observed that locomotor trajectories corresponding to this task were actually stereotyped, both at the geometric and the kinematic levels. In this paper, we propose a computational model for the formation of human locomotor trajectories. Our model is adapted from smoothness maximization models that have been studied in the context of hand trajectory generation. The trajectories predicted by our model are very similar to the experimentally recorded ones. We discuss the theoretical implications of this result in the context of movement planning and control in humans. In particular, this result supports the hypothesis that common principles, such as smoothness maximization, may govern the generation of very different types of movements (in this case, hand movements and whole-body movements).

Numerous data in the literature provide evidence for gender differences in spatial orientation. In particular, it has been suggested that spatial representations of large-scale environments are more accurate in terms of metric information in men than in women but are richer in landmark information in women than in men. One explanatory hypothesis is that men and women differ in terms of navigational processes they used in daily life. The present study investigated this hypothesis by distinguishing two navigational processes: spatial updating by self-motion and landmark-based orientation. Subjects were asked to perform a pointing task in three experimental conditions, which differed in terms of reliability of the external landmarks that could be used. Two groups of subjects were distinguished, a mobile group and an immobile group, in which spatial updating of environmental locations did not have the same degree of importance for the correct performance of the pointing task. We found that men readily relied on an internal egocentric representation of where landmarks were expected to be in order to perform the pointing task, a representation that could be updated during self-motion (spatial updating). In contrast, women seemed to take their bearings more readily on the basis of the stable landmarks of the external world. We suggest that this gender difference in spatial orientation is not due to differences in information processing abilities but rather due to the differences in higher level strategies.

Deciding where to look is mandatory to explore the visual world. To study the neural correlates subserving the cognitive phase of self-initiated eye movements in humans, we tested 12 healthy participants, using event-related functional MRI. Changes in the frontal-cortical activity preceding voluntary saccades were studied when the participants freely decided the direction of a forthcoming saccade, compared with a condition in which they had only to prepare an externally cued saccade. Self-initiation of saccades, before their execution, was specifically associated with frontal-lobe activation in the dorsolateral prefrontal cortex, and in the right presupplementary eye field and frontal eye fields, suggesting the roles of these areas in the decision process of where to look when facing two possible visual targets.

International audience; Few studies have explored how humans memorize landmarks in complex multifloored buildings. They have observed that participants memorize an environment either by floors or by vertical columns, influenced by the learning path. However, the influence of the building's actual structure is not yet known. In order to investigate this influence, we conducted an experiment using an object-in-place protocol in a cylindrical building to contrast with previous experiments which used rectilinear environments. Two groups of 15 participants were taken on a tour with a first person perspective through a virtual cylindrical three-floored building. They followed either a route discovering floors one at a time, or a route discovering columns (by simulated lifts across floors). They then underwent a series of trials, in which they viewed a camera movement reproducing either a segment of the learning path (familiar trials), or performing a shortcut relative to the learning trajectory (novel trials). We observed that regardless of the learning path, participants better memorized the building by floors, and only participants who had discovered the building by columns also memorized it by columns. This expands on previous results obtained in a rectilinear building, where the learning path favoured the memory of its horizontal and vertical layout. Taken together, these results suggest that both learning mode and an environment's structure influence the spatial memory of complex multifloored buildings.

A dual adaptation paradigm was used in order to study the adaptation to two conditions of conflicting visual and kinesthetic and vestibular information. Adaptation was induced in humans by modifying visual information during whole-body rotations with the help of a virtual reality set-up. Real rotations' amplitudes were factored by a gain of 0.5 or 1.5. The two conditions were associated to a visual context cue. The aim of the experiment was to provide support for either the feedback or the feedforward model of adaptive states switch. Results show that subjects could adapt to the two conditions of conflict during whole-body rotations. However, the two conflict situations have been found to differ both in their motor dynamics and in their susceptibility to adaptation, as it seems that the adaptation is more complete in the condition of gain 1.5, i.e., faster and more precise. Subjects could be divided into two groups according to their ability to use contextual information to switch between adaptive gains. The visual cues were sufficient for some subjects to switch adaptive state, which corresponds to a context-dependent dual adaptation, or feedforward model of switching. Other subjects showed a switch cost maintained across the experiment, corresponding with a stimulus-dependent adaptation, or feedback model of switching. We are suggesting that the process enabling switching between adaptive states depends on subjects' abilities to use contextual cues of certain types, and thus on their "perceptive styles". This could explain the variability of results obtained in the literature.

Most studies about human locomotion only tend to consider single subjects walking alone in a stationary environment. Nevertheless, human subjects have often to plan and generate their locomotor trajectories according to one another's displacements. Therefore, in the present study we address the question of the interpersonal coordination when pairs of subjects walk simultaneously. Six pairs of subjects walking face to face, backwards and forwards on a 8 m x 2 m track were involved in our experiment. Within each pair, the leader (L) was required to break the initial interpersonal distance whereas the follower (F) had to maintain this distance constant (1, 2 or 3 m). We measured their position and analyzed their travelled distance, the time course of their linear displacement, and the kinematics parameters of their steps. Our results show that F travels smaller distances than L and that even if they are highly correlated, some temporal delays exist between displacements of L and F with greater values when the interpersonal distance increases (from 1 to 3 m). These results are discussed in terms of high level imitation, i.e. bidirectional interactions with mutual influences of each subject on one another.

Anticipatory head orientation relative to walking direction was investigated in humans. Subjects were asked to walk along a 20 m perimeter, figure of eight. The geometry of this path required subjects to steer their body according to both curvature variations (alternate straight with curved walking) and walking direction (clock wise and counter clock wise). In agreement with previous results obtained during different locomotor tasks [R. Grasso, S. Glasauer, Y. Takei, A. Berthoz, The predictive brain: anticipatory control of head direction for the steering of locomotion, NeuroReport 7 (1996) 1170-1174; R. Grasso, P. Prevost, Y.P. Ivanenko, A. Berthoz, Eye-head coordination for the steering of locomotion in humans: an anticipatory synergy, Neurosci. Lett. 253 (2) (1998) 115-118; T. Imai, S.T. Moore, T. Raphan, B. Cohen, Interaction of body, head, and eyes during walking and turning, Exp. Brain Res. 136 (2001) 1-18; P. Prevost, Y. Ivanenko, R. Grasso, A. Berthoz, Spatial invariance in anticipatory orienting behaviour during human navigation, Neurosci. Lett. 339 (2002) 243-247; G. Courtine, M. Schieppati, Human walking along a curved path. I. Body trajectory, segment orientation and the effect of vision, Eur. J. Neurosci. 18 (2003) 177-190], the head turned toward the future walking direction. This anticipatory head behaviour was continuously modulated by the geometrical variations of the path. Two main components were observed in the anticipatory head behaviour. One was related to the geometrical form of the path, the other to the transfer of body mass from one foot to the other during stepping. A clear modulation of the head deviation pattern was observed between walking on curved versus straight parts of the path: head orientation was influenced to a lesser extent by step alternation for curved path where a transient head fixation was observed. We also observed good symmetry in the head deviation profile, i.e. the head tended to anticipate the future walking direction with the same amplitude when turning to the left (29.75 +/- 7.41 degrees of maximum head deviation) or to the right (30.86 +/- 9.92 degrees ). These findings suggest a combination of motor strategies underlying head stabilization in space and more global orienting mechanisms for steering the whole body in the desired direction.

International audience; On Earth, eye velocity of horizontal optokinetic nystagmus (OKN) orients to gravito-inertial acceleration (GIA), the sum of linear accelerations acting on the head and body. We determined whether adaptation to micro-gravity altered this orientation and whether ocular pursuit exhibited similar properties. Eye movements of four astronauts were recorded with three-dimensional video-oculography. Optokinetic stimuli were stripes moving horizontally, vertically, and obliquely at 30 degrees/s. Ocular pursuit was produced by a spot moving horizontally or vertically at 20 degrees/s. Subjects were either stationary or were centrifuged during OKN with 1 or 0.5 g of interaural or dorsoventral centripetal linear acceleration. Average eye position during OKN (the beating field) moved into the quick-phase direction by 10 degrees during lateral and upward field movement in all conditions. The beating field did not shift up during downward OKN on Earth, but there was a strong upward movement of the beating field (9 degrees) during downward OKN in the absence of gravity; this likely represents an adaptation to the lack of a vertical 1-g bias in-flight. The horizontal OKN velocity axis tilted 9 degrees in the roll plane toward the GIA during interaural centrifugation, both on Earth and in space. During oblique OKN, the velocity vector tilted towards the GIA in the roll plane when there was a disparity between the direction of stripe motion and the GIA, but not when the two were aligned. In contrast, dorsoventral acceleration tilted the horizontal OKN velocity vector 6 degrees in pitch away from the GIA. Roll tilts of the horizontal OKN velocity vector toward the GIA during interaural centrifugation are consistent with the orientation properties of velocity storage, but pitch tilts away from the GIA when centrifuged while supine are not. We speculate that visual suppression during OKN may have caused the velocity vector to tilt away from the GIA during dorsoventral centrifugation. Vertical OKN and ocular pursuit did not exhibit orientation toward the GIA in any condition. Static full-body roll tilts and centrifugation generating an equivalent interaural acceleration produced the same tilts in the horizontal OKN velocity before and after flight. Thus, the magnitude of tilt in OKN velocity was dependent on the magnitude of interaural linear acceleration, rather than the tilt of the GIA with regard to the head. These results favor a 'filter' model of spatial orientation in which orienting eye movements are proportional to the magnitude of low frequency interaural linear acceleration, rather than models that postulate an internal representation of gravity as the basis for spatial orientation.

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.

International audience; It is surprising how quickly we can find our bearings when suddenly confronted with a familiar environment, for instance when the lights are turned on in a dark room. Subjectively, this appears to occur almost instantaneously, yet the neural processes permitting this rapid reorientation are unknown. A likely candidate is the head direction (HD) cell system. These limbic neurons found in several brain regions, including the thalamus and the hippocampus, discharge selectively when the head of an animal is oriented in a particular ("preferred") direction. This neuronal activity is independent of position and ongoing behavior and is thus likely to constitute a physiological basis for the sense of direction. Remarkably, although the HD cell system has properties resembling those of a compass, it is independent of geomagnetic fields. Rather, the preferred directions of the HD cells are strongly anchored to visual cues in the environment. Here, we bring evidence for the first time that a fundamental component of the capacity to rapidly reorient in a familiar environment may be brought about by updating of HD cell responses as rapidly as 80 msec after changes in the visual scene. Continuous attractor networks have been used successfully to model HD cell ensemble dynamics. The present results suggest that after large rotations of the surrounding landmarks, activity in such networks may be propagated in abrupt jumps rather than in a gradually progressive manner.

Five cosmonauts were tested 30 days before a six-month space flight and also on the 2nd and the 6th day after their return to Earth. Cosmonauts performed and imagined a task that involved climbing two stairs to step onto a platform, jumping down with both feet and walking normally for a distance of 4 m. Durations of actual and imagined movements were measured by an electronic stopwatch. Results indicated that cosmonauts performed actual and imagined movements with similar durations before and after the space flight. However, the 2nd day after their return to Earth, cosmonauts significantly increased the durations of both actual and imagined movements. The durations of the imagined and actual movements returned to approximate pre-flight values 6 days after landing. Our results provide evidence that motor imagery process accurately replicates the neural and mechanical modifications which occur during the re-adaptation of the motor system on Earth's gravito-inertial environment after a long space flight.

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.

Les recents developpemets des techniques d’imagerie cerebrale telles que la Tomographie par Emission de Positons (TEP) et l’Imagerie par Resonance Magnetique fonctionnelle (IRMf), ont permis aux chercheurs de determiner plus en detail la neuroanatomie fonctionnelle des reponses emotionnelles. Ces travaux s’inscrivent dans le domaine nouveau des “neurosciences des affects”. Cet article propose une revue des etudes menees sur les structures cerebrales impliquees dans le traitement des expressions faciales emotionnelles d’une part, et dans la reponse emotionnelle induite experimentalement d’autre part. L’implication des resultats et les roles des structures ainsi mises en evidence sont discutes.

Since previous studies showed that loading influences posture and gait, the aim of the present study was to determine the effect of asymmetrical loading on locomotion. The following questions were posed: is there a habituation to asymmetrical loading and what is the effect of immediate unloading? Nine healthy subjects (4 males and 5 females) were tested. They had to memorize visually a triangle drawn on the floor and then to walk clockwise and counterclockwise along it in darkness and blindfolded under the following conditions: baseline, loading of right shoulder with 20% of the body weight, after 30 min of habituation to the weight, and immediately after unloading. The turns in degrees around the angles and the distance of the path in cm were measured. The present study demonstrated that asymmetrical loading, which leads to changes in the somatosensory afferentation, affects the human locomotor pattern. There is a habituation effect as well as an unloading effect. There was also a difference between the changes in clockwise and counterclockwise locomotion. Several hypotheses are discussed to explain the results obtained under all conditions.

Although extensively investigated in socio-cognitive neuroscience, empathy is difficult to study. The first difficulty originates in its multifaceted nature. According to the multidimensional model, empathy combines emotional, automatic (simulation), cognitive (mentalizing) and regulatory (executive functions) processes. Substantial functional magnetic resonance imaging (fMRI) data demonstrated that co-activations in the mirror neuron system (MNS) and mentalizing network (MENT) sustain this co-recruitment of so-called first- and second-person-like processes. Because of the poor temporal resolution of fMRI techniques, we currently lack evidence about the precise timing of the MNS-MENT combination. An important challenge is, thus, to disentangle how MNS and MENT dynamically work together along time in empathy. Moreover, the role of the executive functions in the MNS-MENT combination time course is still unknown. Second, empathy - feeling into - is closely related to sympathy - feeling with - and both phenomena are often conflated in experimental studies on intersubjectivity. In this electrical neuroimaging (EEG) pilot-study, we tested whether the egocentered vs. heterocentered visuo-spatial mechanisms respectively associated with sympathy and empathy differentially modulate the dynamic combination of the MNS-MENT activations in their respective neural time course. For that, we employed our newly developed behavioral paradigm assessing the visuo-spatial - but not emotional - features of empathy and sympathy. Using a data-driven approach, we report that empathy and sympathy are underlied by sequential activations in the MNS from the insula to the inferior frontal gyrus (IFG) between 63ms and 424ms. However, at 333-424ms, empathy triggered greater co-activations in the right IFG and dorsolateral prefrontal cortex (dlPFC) (executive functions). Linking together our present and prior (Thirioux et al., 2010) findings from the same dataset, we suggest that this greater recruitment of the right dlPFC monitors the shift from egocentered and first-person-like mechanisms in the MNS to heterocentered and second-person-like mechanisms in the left temporo-parietal junction within the MENT, i.e., reflecting the onset of perspective-change processes in the neural time course of empathy. Contrasting with sympathy, this recruitment of the executive functions could modulate the output end of the mirroring processing in the premotor and sensorimotor cortices.

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.

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.

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.

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.

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.

International audience; Recent psychophysical studies on normal subjects, as well as brain imaging studies, have revised the concepts concerning the mechanisms underlying spatial orientation during navigation tasks. The emphasis has been put on internal models that allow the prediction of a planned trajectory and are essential in the steering of locomotion. Cognitive factors such as strategies and emotional parameters are now starting to be included in the research on spatial orientation. It is obvious that important individual and gender differences exist in the brain operations underlying spatial orientation in humans, which may help to understand the construction of a coherent perception and the organic neural disorders related to the internal representation of space.

The aim of this study was to examine whether the chronic loss of vestibular function modifies perceptual and oculomotor responses during torso rotations in darkness. Subjects (4 patients with complete vestibular loss and 7 healthy volunteers) were seated on a rotating chair. Stimuli consisted of sinusoidal chair rotations ( ± 30 ∘ , 0.1 Hz and 0.011 Hz). We used 2 conditions: space stationary head (neck stimulation) and space stationary head and shoulders (torso stimulation). Horizontal eye deviations and slow component of eye movements were analysed. The results showed that eye movements and perception of head motion in space during neck stimulation were similar to those during torso stimulation both in normal and labyrinthine-defective (LD) subjects. During low-frequency chair rotations (0.011 Hz) all subjects perceived illusory head or head and shoulder rotation in space (as if the lower part of the body was stationary relative to the room) and shifted their gaze in the direction of illusory head rotation. In these conditions there was no significant difference in eye movements between normal and LD subjects. During higher frequency chair rotations (0.1 Hz), LD subjects had significantly larger eye deviations as well as increases in the gain of the slow component of eye movements relative to normals. In these conditions patients mostly perceived illusory head or head and shoulder rotation in space while normal subjects mainly perceived the head as stationary in space. The results indicate that 1) neck and torso rotations can evoke similar ocular responses in LD subjects, 2) the chronic loss of vestibular function modifies the representation of axial body segment motion relative to space.

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.

Pontine omnipause neurons (OPNs) have so far been considered as forming a homogeneous group of neurons whose tonic firing stops during the duration of saccades, when the head is immobilized. In cats, they pause for the total duration of gaze shifts, when the head is free to move. In the present study, carried out on alert cats with fixed heads, we present observations made dur- ing self-initiated saccades and during tracking of a mov- ing target which show that the OPN population is not ho- mogeneous. Of the 76 OPNs we identified, 39 were found to have characteristics similar to those of previ- ously described neurons, "saccade" (S-) OPNs: (1) the durations of their pauses were significantly correlated with the durations of saccades; (2) the discharge ceased shortly before saccade onset and resumed before saccade end; (3) visual responses to target motion were excitato- ry; and (4) during tracking, S-OPNs interrupted the dis- charge for the duration of saccades and resumed firing during perisaccadic "drifts". However, the characteristics of 37 neurons ("complex" (C-) OPNs) were different: (1) the pause duration was not correlated with the duration of self-initiated saccades; (2) time lead of pause onsets relative to saccades was, on average, longer than in the group of S-OPNs, and firing resumed after the saccade end; (3) visual target motion suppressed tonic discharg- es; and (4) during tracking, firing was interrupted for the total duration of gaze shifts, including not only saccades but also perisaccadic "drifts". We conclude that cat OPNs can be subdivided into two main groups. The first comprises neurons whose firing patterns are compatible with gating individual saccades ("saccade" OPNs). The second group consists of "complex" OPNs whose firing characteristics are appropriate to gate total gaze displace- ments rather than individual saccades. The function of these neurons may be to disinhibit pontobulbar circuits participating in the generation of saccade sequences and associated perisaccadic drifts.

We investigated head and gaze orientation in six healthy volunteers walking along 90 degrees corner trajectories, both at light and with eyes closed. We found that head and eyes systematically deviated toward the future direction of the curved trajectory. Anticipation lead was about 1 s. Strikingly, the same behaviour was observed in darkness. In backward (BW) locomotion along the trajectory (from end- to start-point), gaze deviated toward the opposite direction, such that the forward locomotor pattern did not appear time-reversed. Orienting movements displayed higher amplitude, reproducibility and time lead in the forward (FW) direction at light. We suggest that anticipatory orienting synergies belong to the behavioural repertoire of human navigation and may reflect the need to prepare a stable reference frame for intended action.

Vestibular perception of whole-body passive rotation in the horizontal plane was studied by applying two-dimensional (2D) motion to eight blindfolded healthy volunteers: pure rotations in place, corner-like trajectories and arcs of a circular trajectory were randomly applied by means of a remotely controlled robot. Angles embedded in the 2D trajectories were 45 degrees, 90 degrees, 135 degrees and 180 degrees. Stimulation of semicircular canals was the same for all trajectories but was accompanied by concurrent otolith stimulation during circular motion. Subjects participated in two successive experimental sessions. In the first session they were instructed to use a pointer to reproduce the total angular displacement after the motion (REPRODUCTION); in the second session they had to keep pointing towards a remote (15 m) memorised target during the motion (TRACKING). In REPRODUCTION subjects tended to overestimate their rotation angle by 28 +/- 11% (mean +/- SD). There was no systematic effect of the trajectory. Overestimation also occurred when subjects were required to rotate in darkness by 180 degrees (by controlling a joystick). In TRACKING there was virtually no overestimation (6 +/- 17%) and the movement of the pointer matched the dynamics of angular motion. We conclude that (a) the brain can separate and memorise the angular component of complex 2D motion; however, a large inter-individual variability in estimating its amplitude exists; (b) in the range of linear accelerations used in the study, no appreciable effect of otolith-canal perceptual interaction was shown; (c) angular displacements can be dynamically transformed into matched pointing movements; (d) overestimation seems to be typical of delayed judgements of angular displacement and of self-controlled rotations in place. This could be due to the characteristics of the physiological calibration of the vestibular input.

International audience; Eight healthy subjects were asked to walk blindfolded along circular paths of different radii after several practice trials with vision. Their task was to stop after completing two full revolutions. They always walked counter-clockwise (CCW) in (a) a control condition (CONTROL), including the instructions mentioned above, (b) with the further instruction to count backwards in twos (MENTAL), (c) with the instruction to count loudly (LOUD). The movement of two markers lying along the head naso-occipital axis was recorded by means of an ELITE system. Total walked distance (DISTANCE), total head turning angle (ANGLE) and average radius (RADIUS) of the trajectories performed were measured. All subjects were able to perform approximately circular trajectories. They consistently overshot the ideal radius independently of the condition and circle size, undershot the total angle and overshot total distance. The LOUD condition induced greater errors in the performance but only on total distance (P

Israël, I., R. Grasso, P. Georges-François, T. Tsuzuku, and A. Berthoz. Spatial memory and path integration studied by self-driven passive linear displacement. I. Basic properties. J. Neurophysiol. 77: 3180–3192, 1997. According to path integration, the brain is able to compute the distance of a traveled path. In this research we applied our previously reported method for studying memory of linear distance, a crucial mechanism in path integration; our method is based on the overt reconstruction of a passive transport. Passive transport is a special case of navigation in which no active control is performed. Blindfolded subjects were first asked to travel 2 m forward, in darkness, by driving with a joystick the robot on which they were seated. The results show that all subjects but two undershot this distance, i.e., overestimated their own displacement. Then, subjects were submitted to a passive linear forward displacement along 2, 4, 6, 8, or 10 m, and had to reproduce the same distance, still blindfolded. The results show that the distance of the stimulus was accurately reproduced, as well as stimulus duration, peak velocity, and velocity profile. In this first condition, the imposed velocity profile was triangular and therefore stimulus distance and duration were correlated. In a second condition, it was shown that distance was correctly reproduced also when the information about stimulus duration was kept constant. Here, different velocity profiles were used as stimuli, and most subjects also reproduced the velocity profile. Statistical analyses indicated that distance was not reproduced as a consequence of duration, peak velocity, or velocity profile reproduction, but was uniquely correlated to stimulus distance. The previous hypothesis of a double integration of the otolith signal to provide a distance estimate can explain our results. There was a large discrepancy between the accuracy with which the subjects matched the velocity profiles and that of distance reproduction. It follows that, whereas the dynamics of passive motion are stored and available to further use, distance is independently estimated. It is concluded that vestibular and somatosensory signals excited by passive transport can be used to build a dynamic as well as a static representation of the traveled path. We found a close quantitative similarity between the present findings on distance reproduction and those obtained from active locomotion experiments in which the same paradigm was used. This resemblance suggests that the two types of navigation tasks draw on common physiological processes and extends the relevance of our results to naturally occurring path integration.

We have recently reported that the head systematically deviates toward the future direction of the trajectory about 500 ms before attaining a turning point of 90° corner trajectories both in light and in darkness. Here, we investigated how this anticipatory strategy is modified whilst varying visual conditions (Experiment 1) and walking speed (Experiment 2). Exp. 1 showed similar anticipatory behaviour when walking with or without vision. Exp. 2 (that varied walking speed; eyes open) showed that the head started to deviate at a constant distance rather than at a constant time to the corner. The results appear inconsistent with optic flow theories of the guidance of walking direction and might highlight the role of landmarks and/or egocentric direction in anticipatory orienting behaviour.

In goal-oriented locomotion, healthy adults generate highly stereotyped trajectories and a consistent anticipatory head orienting behaviour, both evidence of top-down, open-loop control. The aim of this study is to describe the typical development of anticipatory orienting strategies and trajectory formation. Our hypothesis is that full-blown anticipatory control requires advanced navigational skills. Twenty-six healthy subjects (14 children: 4-11 years; 6 adolescents: 13-17 years; 6 adults) were asked to walk freely towards one of the three visual targets, in a randomised order. Movement was captured via an optoelectronic system, with 15 body markers. The whole-body displacement, yaw orientation of head, trunk and pelvis, heading direction and foot placements were extracted. Head-heading anticipation, trajectory curvature, indexes of variability of trajectories, foot placements and kinematic profiles were studied. The mean head-heading anticipation time and trajectory curvature did not significantly differ among age groups. In children, however, head anticipation was more often lacking (χ2 = 9.55, p0.01), and there were significant intra- and inter-subject variations. Trajectory curvature was often very high in children, while it became consistently lower in adolescence (χ2 = 78.59, p10(-17)). The indexes of spatial and kinematic variability all followed a decreasing developmental trend (R (2)0.5, p0.0001). In conclusion, children under 11 do not perform curvilinear locomotor trajectories as adolescents and adults do. Anticipatory head orientation and trajectory formation develop in late childhood, well after gait maturation. Navigational skills, such as path planning and shifting from ego- to allocentric spatial reference frames, are proposed as necessary requisites for mature locomotor control.

International audience; In the present study, we investigated the effect of weightlessness on the ability to perceive and remember self-motion when passing through virtual 3D tunnels that curve in different direction (up, down, left, right). We asked cosmonaut subjects to perform the experiment before, during and after long-duration space flight aboard the International Space Station (ISS), and we manipulated vestibular versus haptic cues by having subjects perform the task either in a rigidly fixed posture with respect to the space station or during free-floating, in weightlessness. Subjects were driven passively at constant speed through the virtual 3D tunnels containing a single turn in the middle of a linear segment, either in pitch or in yaw, in increments of 12.5°. After exiting each tunnel, subjects were asked to report their perception of the turn’s angular magnitude by adjusting, with a trackball, the angular bend in a rod symbolizing the outside view of the tunnel. We demonstrate that the strong asymmetry between downward and upward pitch turns observed on Earth showed an immediate and significant reduction when free-floating in weightlessness and a delayed reduction when the cosmonauts were firmly in contact with the floor of the station. These effects of weightlessness on the early processing stages (vestibular and optokinetics) that underlie the perception of self-motion did not stem from a change in alertness or any other uncontrolled factor in the ISS, as evidenced by the fact that weightlessness had no effect on the perception of yaw turns. That the effects on the perception of pitch may be partially overcome by haptic cues reflects the fusion of multisensory cues and top-down influences on visual perception.

We have used positron emission tomography (PET) to study the functional anatomy of the repetition of a prelearned sequence of horizontal saccadic eye movements. Five subjects had to memorize a sequence of six successive horizontal saccades. The subjects were scanned in total darkness under three different conditions: at rest, during the execution of self-paced horizontal saccades, and while repeating a prelearned saccades sequence. The repetition of the prelearned saccades sequence led to specific normalized regional cerebral blood flow (NrCBF) increases at the depth of the superior frontal sulcus as well as at the rostral part of the supplementary motor area, whereas at the parietal level an important activation was observed in the intraparietal sulcus extending up to the precuneus. In addition, it was noticed that compared with the resting control condition, both oculomotor tasks activated a common set of cortical and subcortical areas. At the cortical level, this network was composed of the frontal eye fields, the supplementary eye fields, the median part of the cingulate gyrus, and the insula. At the subcortical level, the lenticular nucleus and the thalamus as well as the cerebellar vermis were activated consistently. A direct comparison of our results with those of other PET studies on spatial vision suggests that the dorsal visuospatial pathway could be extended toward the frontal premotor region. In such a scheme, visuospatial information computed in the intraparietal sulcus would be transmitted to the frontal premotor cortex to optimize a spatial-oriented behavior. This is consistent with the early proposal that perceptual and intentional components of spatial information are mediated through superior parietal and frontal areas, respectively.