How the cerebellum may monitor sensory information for spatial representation

The cerebellum has already been shown to participate in the navigation function. We propose here that this structure is involved in maintaining a sense of direction and location during self-motion by monitoring sensory information and interacting with navigation circuits to update the mental representation of space. To better understand the processing performed by the cerebellum in the navigation function, we have reviewed: the anatomical pathways that convey self-motion information to the cerebellum; the computational algorithm(s) thought to be performed by the cerebellum from these multi-source inputs; the cerebellar outputs directed toward navigation circuits and the influence of self-motion information on space-modulated cells receiving cerebellar outputs. This review highlights that the cerebellum is adequately wired to combine the diversity of sensory signals to be monitored during self-motion and fuel the navigation circuits. The direct anatomical projections of the cerebellum toward the head-direction cell system and the parietal cortex make those structures possible relays of the cerebellum influence on the hippocampal spatial map. We describe computational models of the cerebellar function showing that the cerebellum can filter out the components of the sensory signals that are predictable, and provides a novelty output. We finally speculate that this novelty output is taken into account by the navigation structures, which implement an update over time of position and stabilize perception during navigation

Predictive maps in rats and humans for spatial navigation

Much of our understanding of navigation comes from the study of individual species, often with specific tasks tailored to those species. Here, we provide a novel experimental and analytic framework integrating across humans, rats, and simulated reinforcement learning (RL) agents to interrogate the dynamics of behavior during spatial navigation. We developed a novel open-field navigation task ("Tartarus maze") requiring dynamic adaptation (shortcuts and detours) to frequently changing obstructions on the path to a hidden goal. Humans and rats were remarkably similar in their trajectories. Both species showed the greatest similarity to RL agents utilizing a "successor representation," which creates a predictive map. Humans also displayed trajectory features similar to model-based RL agents, which implemented an optimal tree-search planning procedure. Our results help refine models seeking to explain mammalian navigation in dynamic environments and highlight the utility of modeling the behavior of different species to uncover the shared mechanisms that support behavior

Hippocampal place cells encode global location but not changes in environmental connectivity in a 4-room navigation task

Flexible navigation relies on a cognitive map of space, thought to be implemented by hippocampal place cells: neurons that exhibit location-specific firing. In connected environments, optimal navigation requires keeping track of one’s location and of the available connections between subspaces. We examined whether the dorsal CA1 place cells of rats encode environmental connectivity in four geometrically identical boxes arranged in a square. Rats moved between boxes by pushing saloon-type doors that could be locked in one or both directions. Although rats demonstrated knowledge of environmental connectivity, their place cells did not respond to connectivity changes, nor did they represent doorways differently from other locations. Place cells coded location in a global reference frame, with a different map for each box and minimal repetitive fields despite the repetitive geometry. These results suggest that CA1 place cells provide a spatial map that does not explicitly include connectivity

Environmental metabarcoding reveals contrasting belowground and aboveground fungal communities from poplar at a Hg phytomanagement site

Characterization of microbial communities in stressful conditions at a field level is rather scarce, especially when considering fungal communities from aboveground habitats. We aimed at characterizing fungal communities from different poplar habitats at a Hg-contaminated phytomanagement site by using Illumina-based sequencing, network analysis approach, and direct isolation of Hg-resistant fungal strains. The highest diversity estimated by the Shannon index was found for soil communities, which was negatively affected by soil Hg concentration. Among the significant correlations between soil operational taxonomic units (OTUs) in the co-occurrence network, 80% were negatively correlated revealing dominance of a pattern of mutual exclusion. The fungal communities associated with Populus roots mostly consisted of OTUs from the symbiotic guild, such as members of the Thelephoraceae, thus explaining the lowest diversity found for root communities. Additionally, root communities showed the highest network connectivity index, while rarely detected OTUs from the Glomeromycetes may have a central role in the root network. Unexpectedly high richness and diversity were found for aboveground habitats, compared to the root habitat. The aboveground habitats were dominated by yeasts from the Lalaria, Davidiella, and Bensingtonia genera, not detected in belowground habitats. Leaf and stem habitats were characterized by few dominant OTUs such as those from the Dothideomycete class producing mutual exclusion with other OTUs. Aureobasidium pullulans, one of the dominating OTUs, was further isolated from the leaf habitat, in addition to Nakazawaea populi species, which were found to be Hg resistant. Altogether, these findings will provide an improved point of reference for microbial research on inoculation-based programs of tailings dumps

Chinese Languages spoken in Mauritius: An Overview

Citation: Julie Lefort, Chinese Languages spoken in Mauritius: An Overview, Lame dan lame? La main dans la main? Hand in Hand? Conference, University of Mauritius and University of Wollongong, 2019. Abstract: Up to now, studies on the Chinese community of Mauritius have mainly focused on Chinese immigration and settlement from a historical point of view and little attention has been given to Chinese languages and linguistic practices involving Chinese languages. Although different varieties of Chinese are spoken in Mauritius, namely Hakka, Hokkien, Cantonese, and to some extent, Standard Mandarin, the few studies on Chinese languages of Mauritius have focused on the Meixian-Hakka language, which is often seen as the only variety spoken in Mauritius. In this article I provide an overview of the Chinese languages spoken in Mauritius from a sociolinguistic perspective. I give an introduction about the history of Chinese immigration to Mauritius in order to understand how these varieties have led to today’s situation and will show that the Chinese community of Mauritius is not as homogeneous as it is often believed to be. I will try to classify the different speakers according to the Chinese variety they speak and their situation, giving concrete examples of families in which this particular variety is spoken. I will show that the Chinese languages spoken in Mauritius can be classified between ancestral transmitted ones and imported vehicular ones

Rôle du LTP cérébelleux à fibre parallèle : synapses Purkinje cellulaires dans la navigation spatiale

La navigation spatiale peut être subdivisée en deux processus: la construction d’une représentation mentale de l’espace à partir de l’exploration de l’environnement d'une part, et l’utilisation de cette représentation de façon à produire le trajet le plus adapté pour rejoindre le lieu souhaité d'autre part. Lors de l’exploration de l’environnement, des informations externes et des informations de mouvement propre (i.e. vestibulaires et proprioceptives) sont combinées pour former la carte cognitive. Depuis longtemps des études suggèrent que le cervelet participe à la navigation spatiale mais son rôle a souvent été confiné à l’exécution motrice. Notre équipe a étudié des souris mutantes L7-PKCI présentant un déficit de plasticité synaptique de type dépression à long terme (DLT) au niveau des synapses entre fibres parallèles et cellules de Purkinje du cortex cérébelleux. Ces travaux ont montré que les souris présentent à la fois un déficit dans l'optimisation de la trajectoire mais également dans le maintien de la carte cognitive formée dans l'hippocampe. En effet, les propriétés de décharge des cellules de lieu de l'hippocampe sont affectées chez ces souris exclusivement lorsque celles-ci doivent naviguer en se reposant sur les informations provenant de leur mouvement propre, c'est à dire quand elles explorent l'environnement dans le noir. A ces mêmes synapses, une plasticité de type potentialisation à long terme (PLT) a été observée et permet (avec la DLT) la modulation bidirectionelle de l’efficacité synaptique. La plasticité bidirectionnelle est un processus clé dans les modèles théoriques de type « filtre adaptatif » de traitement de l’information par le cervelet. Selon ces modèles, l’absence de PLT ou DLT devrait affecter de façon similaire la plasticité bidirectionnelle et conduire ainsi à des déficits comparables. Pour tester cette hypothèse, nous avons étudié les conséquences fonctionnelles d’un déficit de type PLT au niveau de la même synapse entre fibre parallèle et cellule de Purkinje. Nous avons utilisé la lignée transgénique L7-PP2B, spécifiquement déficitaire pour cette plasticité.Malgré un léger déficit moteur révélé exclusivement sur le rotarod, les capacités de navigation des souris L7-PP2B ne sont pas affectées dans une tâche de navigation en labyrinthe aquatique de type piscine de Morris. Les propriétés des cellules de lieu de l’hippocampe des souris L7-PP2B ont ensuite été caractérisées lors de l’exploration d’une arène circulaire dans différentes conditions environnementales. Contrairement à celles des souris L7-PKCI, les propriétés des cellules de lieux des souris L7-PP2B ne sont pas affectées lorsque les souris ne peuvent utiliser que les informations de mouvement propre pour s’orienter, c'est à dire dans le noir. Par contre, les cellules de lieux des souris L7-PP2B présentent une instabilité en l’absence de toute manipulation d’indice environnemental, dans 23% des sessions d’enregistrement. Cette instabilité, absente chez les souris contrôles, se manifeste de façon imprévisible dans un environnement familier et est caractérisée par une rotation angulaire cohérente de l’ensemble des cellules de lieux enregistrées. Ces données suggèrent qu’en l’absence de PLT cérébelleuse la représentation spatiale de l’hippocampe n’est pas ancrée de façon stable aux indices externes proximaux. Ces résultats, associés à ceux des souris L7-PKCI indiquent que le cervelet contribue de manière complexe à la fois à la représentation spatiale hippocampique et aux capacités de navigation et que DLT et PLT jouent probablement des rôles différents dans ces processus.Spatial navigation can be divided into two processes: building a spatial representation from the environment exploration and using this representation to produce an adapted trajectory toward a goal. During the environment exploration, external and self-motion information (i.e. vestibular and proprioceptive) are combined to form the spatial map. It has long been suggested that the cerebellum participates in spatial navigation but its role has often been confined to motor execution. Our team has studied L7-PKCI mice which lack a plasticity mechanism (long term depression (LTD)) at parallel fiber-Purkinje cell synapses in the cerebellar cortex. These works have shown that L7-PKCI mice present a deficit in trajectory optimization as well as in the maintenance of the cognitive map in the hippocampus. Indeed in these mice, the firing properties of hippocampal place cells are affected specifically when mice have to rely on self-motion information, i.e. when exploring the environment in the dark.A these same synapses, another type of plasticity (long term potentiation (LTP)) has been described, and allows (with LTD) the bidirectional modulation of the synaptic efficiency. Bidirectional plasticity is a key element of the ‘adaptive filter’ theoretical models of cerebellar information processing. According to these models, a lack of LTP or LTD should similarly affect bidirectional plasticity and result in comparable deficits. To test this prediction, we investigated the functional consequences of a deficit of LTP at parallel fiber-Purkinje cell synapses using the L7-PP2B mice model, specifically impaired for this plasticity.In spite of a mild motor adaptation deficit, revealed on the rotarod task, spatial learning of L7-PP2B mice was not impaired in the watermaze task. Hippocampal place cell properties of L7-PP2B mice were characterized during exploration of a circular arena, following different experimental manipulations. In contrast to mice lacking cerebellar LTD, place cells properties of L7-PP2B mice were not impaired when mice had to rely on self-motion cues, i.e. in the dark. Surprisingly, L7-PP2B place cells displayed instability in the absence of any proximal cue manipulation in 23 % of the recording sessions. This instability occurred in an unpredictable way in a familiar environment and was characterized each time by a coherent angular rotation of the whole set of recorded place cells. These data suggest that, in the absence of cerebellar LTP, hippocampal spatial representation cannot be reliably anchored to the proximal cue. These results along with those from L7­PKCI mice, indicate that the cerebellum contributes to both hippocampal representation and subsequent navigation abilities and that LTP and LTD are likely to play different roles in these processes

Rôle du LTP cérébelleux à fibre parallèle : synapses Purkinje cellulaires dans la navigation spatiale

Spatial navigation can be divided into two processes: building a spatial representation from the environment exploration and using this representation to produce an adapted trajectory toward a goal. During the environment exploration, external and self-motion information (i.e. vestibular and proprioceptive) are combined to form the spatial map. It has long been suggested that the cerebellum participates in spatial navigation but its role has often been confined to motor execution. Our team has studied L7-PKCI mice which lack a plasticity mechanism (long term depression (LTD)) at parallel fiber-Purkinje cell synapses in the cerebellar cortex. These works have shown that L7-PKCI mice present a deficit in trajectory optimization as well as in the maintenance of the cognitive map in the hippocampus. Indeed in these mice, the firing properties of hippocampal place cells are affected specifically when mice have to rely on self-motion information, i.e. when exploring the environment in the dark.A these same synapses, another type of plasticity (long term potentiation (LTP)) has been described, and allows (with LTD) the bidirectional modulation of the synaptic efficiency. Bidirectional plasticity is a key element of the ‘adaptive filter’ theoretical models of cerebellar information processing. According to these models, a lack of LTP or LTD should similarly affect bidirectional plasticity and result in comparable deficits. To test this prediction, we investigated the functional consequences of a deficit of LTP at parallel fiber-Purkinje cell synapses using the L7-PP2B mice model, specifically impaired for this plasticity.In spite of a mild motor adaptation deficit, revealed on the rotarod task, spatial learning of L7-PP2B mice was not impaired in the watermaze task. Hippocampal place cell properties of L7-PP2B mice were characterized during exploration of a circular arena, following different experimental manipulations. In contrast to mice lacking cerebellar LTD, place cells properties of L7-PP2B mice were not impaired when mice had to rely on self-motion cues, i.e. in the dark. Surprisingly, L7-PP2B place cells displayed instability in the absence of any proximal cue manipulation in 23 % of the recording sessions. This instability occurred in an unpredictable way in a familiar environment and was characterized each time by a coherent angular rotation of the whole set of recorded place cells. These data suggest that, in the absence of cerebellar LTP, hippocampal spatial representation cannot be reliably anchored to the proximal cue. These results along with those from L7­PKCI mice, indicate that the cerebellum contributes to both hippocampal representation and subsequent navigation abilities and that LTP and LTD are likely to play different roles in these processes.La navigation spatiale peut être subdivisée en deux processus: la construction d’une représentation mentale de l’espace à partir de l’exploration de l’environnement d'une part, et l’utilisation de cette représentation de façon à produire le trajet le plus adapté pour rejoindre le lieu souhaité d'autre part. Lors de l’exploration de l’environnement, des informations externes et des informations de mouvement propre (i.e. vestibulaires et proprioceptives) sont combinées pour former la carte cognitive. Depuis longtemps des études suggèrent que le cervelet participe à la navigation spatiale mais son rôle a souvent été confiné à l’exécution motrice. Notre équipe a étudié des souris mutantes L7-PKCI présentant un déficit de plasticité synaptique de type dépression à long terme (DLT) au niveau des synapses entre fibres parallèles et cellules de Purkinje du cortex cérébelleux. Ces travaux ont montré que les souris présentent à la fois un déficit dans l'optimisation de la trajectoire mais également dans le maintien de la carte cognitive formée dans l'hippocampe. En effet, les propriétés de décharge des cellules de lieu de l'hippocampe sont affectées chez ces souris exclusivement lorsque celles-ci doivent naviguer en se reposant sur les informations provenant de leur mouvement propre, c'est à dire quand elles explorent l'environnement dans le noir. A ces mêmes synapses, une plasticité de type potentialisation à long terme (PLT) a été observée et permet (avec la DLT) la modulation bidirectionelle de l’efficacité synaptique. La plasticité bidirectionnelle est un processus clé dans les modèles théoriques de type « filtre adaptatif » de traitement de l’information par le cervelet. Selon ces modèles, l’absence de PLT ou DLT devrait affecter de façon similaire la plasticité bidirectionnelle et conduire ainsi à des déficits comparables. Pour tester cette hypothèse, nous avons étudié les conséquences fonctionnelles d’un déficit de type PLT au niveau de la même synapse entre fibre parallèle et cellule de Purkinje. Nous avons utilisé la lignée transgénique L7-PP2B, spécifiquement déficitaire pour cette plasticité.Malgré un léger déficit moteur révélé exclusivement sur le rotarod, les capacités de navigation des souris L7-PP2B ne sont pas affectées dans une tâche de navigation en labyrinthe aquatique de type piscine de Morris. Les propriétés des cellules de lieu de l’hippocampe des souris L7-PP2B ont ensuite été caractérisées lors de l’exploration d’une arène circulaire dans différentes conditions environnementales. Contrairement à celles des souris L7-PKCI, les propriétés des cellules de lieux des souris L7-PP2B ne sont pas affectées lorsque les souris ne peuvent utiliser que les informations de mouvement propre pour s’orienter, c'est à dire dans le noir. Par contre, les cellules de lieux des souris L7-PP2B présentent une instabilité en l’absence de toute manipulation d’indice environnemental, dans 23% des sessions d’enregistrement. Cette instabilité, absente chez les souris contrôles, se manifeste de façon imprévisible dans un environnement familier et est caractérisée par une rotation angulaire cohérente de l’ensemble des cellules de lieux enregistrées. Ces données suggèrent qu’en l’absence de PLT cérébelleuse la représentation spatiale de l’hippocampe n’est pas ancrée de façon stable aux indices externes proximaux. Ces résultats, associés à ceux des souris L7-PKCI indiquent que le cervelet contribue de manière complexe à la fois à la représentation spatiale hippocampique et aux capacités de navigation et que DLT et PLT jouent probablement des rôles différents dans ces processus

The cerebellum: a new key structure in the navigation system

Early investigations of cerebellar function focused on motor learning, in particular on eyeblink conditioning and adaptation of the vestibulo-ocular reflex, and led to the general view that cerebellar Long Term Depression (LTD) at parallel fiber-Purkinje cell synapses is the neural correlate of cerebellar motor learning. Thereafter, while the full complexity of cerebellar plasticities was being unraveled, cerebellar involvement in more cognitive tasks - including spatial navigation - was further investigated. However, cerebellar implication in spatial navigation remains a matter of debate because motor deficits frequently associated with cerebellar damage often prevent the dissociation between its role in spatial cognition from its implication in motor function. Here, we review recent findings from behavioral and electrophysiological analyses of cerebellar mutant mouse models, which show that the cerebellum might participate in the construction of hippocampal spatial representation map (i.e. place cells) and thereby in goal-directed navigation. These recent advances in cerebellar research point toward a model in which computation from the cerebellum could be required for spatial representation and would involve the integration of multi-source self-motion information to: 1) transform the reference frame of vestibular signals and 2) distinguish between self- and externally-generated vestibular signals. We eventually present herein anatomical and functional connectivity data supporting a cerebello-hippocampal interaction. Whilst a direct cerebello-hippocampal projection has been suggested, recent investigations rather favor a multi-synaptic pathway involving posterior parietal and retrosplenial cortices, two regions critically involved in spatial navigation

Acquisition of an olfactory associative task triggers a regionalized down-regulation of adult born neuron cell death

International audienc

Cerebellar Contribution to Spatial Navigation: New Insights into Potential Mechanisms

SIXTH INTERNATIONAL SYMPOSIUM OF SRC, Rome, ITALY, JUL 03-04, 2014International audienceThe contribution of the cerebellum to the non-motor aspects of spatial navigation is now established, but the mechanisms of its participation remain unclear. The L7-PKCI mouse model, in which inhibited PKC activity suppresses parallel fiber-Purkinje cell long-term depression (LTD), provides the opportunity to study their spatial abilities in the absence of any motor impairment. L7-PKCI mice are deficient in the spatial but not the cued version of the watermaze task. Their performances are preserved when alleys guide their trajectories in the starmaze task, suggesting that cerebellar PKC-dependent mechanisms are required for the production of an optimal trajectory toward a goal. Furthermore, electrophysiological recordings in freely moving L7-PKCI mice revealed that their hippocampal place cell properties are affected when they have to rely on self motion information: in the absence of external information as well as in a conflicting situation between self-motion and external information. This suggests that the cerebellum is involved in the processing of self-motion information and is required for the construction of the spatial representation in the hippocampus