Is there a pilot in the brain? Contribution of the self-positioning system to spatial navigation

International audienceSince the discovery of place cells, the hippocampus is thought to be the neural substrate of a cognitive map. The later discovery of head direction cells, grid cells and border cells, as well as of cells with more complex spatial signals, has led to the idea that there is a brain system devoted to providing the animal with the information required to achieve efficient navigation. Current questioning is focused on how these signals are integrated in the brain. In this review, we focus on the issue of how self-localization is performed in the hippocampal place cell map. To do so, we first shortly review the sensory information used by place cells and then explain how this sensory information can lead to two coding modes, respectively based on external landmarks (allothetic information) and self-motion cues (idiothetic information). We hypothesize that these two modes can be used concomitantly with the rat shifting from one mode to the other during its spatial displacements. We then speculate that sequential reactivation of place cells could participate in the resetting of self-localization under specific circumstances and in learning a new environment. Finally, we provide some predictions aimed at testing specific aspects of the proposed ideas

Kv4 potassium channels modulate hippocampal EPSP-spike potentiation and spatial memory in rats

International audienceKv4 channels regulate the backpropagation of action potentials (b-AP) and have been implicated in the modulation of longterm potentiation (LTP). Here we showed that blockade of Kv4 channels by the scorpion toxin AmmTX3 impaired reference memory in a radial maze task. In vivo, AmmTX3 intracerebroventricular (i.c.v.) infusion increased and stabilized the EPSP-spike (E-S) component of LTP in the dentate gyrus (DG), with no effect on basal transmission or short-term plasticity. This increase in E-S potentiation duration could result from the combination of an increase in excitability of DG granular cells with a reduction of GABAergic inhibition, leading to a strong reduction of input specificity. Radioactive in situ hybridization (ISH) was used to evaluate the amounts of Kv4.2 and Kv4.3 mRNA in brain structures at different stages of a spatial learning task in naive, pseudoconditioned, and conditioned rats. Significant differences in Kv4.2 and Kv4.3 mRNA levels were observed between conditioned and pseudoconditioned rats. Kv4.2 and Kv4.3 mRNA levels were transiently up-regulated in the striatum, nucleus accumbens, retrosplenial, and cingulate cortices during early stages of learning, suggesting an involvement in the switch from egocentric to allocentric strategies. Spatial learning performance was positively correlated with the levels of Kv4.2 and Kv4.3 mRNAs in several of these brain structures. Altogether our findings suggestthat Kv4 channels could increase the signal-to-noise ratio during information acquisition, thereby allowing a better encoding of the memory trace

Interactive Design of Sustainable Cities with a Distributed Local Search Solver

International audienceWithin the last decades, the design of more sustainable cities has emerged as a central society issue. A city, in the early stage of its design process, is modeled as a balanced set of urban shapes (residential, commercial, or industrial units, together with infrastructures, schools, parks) that need to be spatially organized following complex rules. To assist urban planners and decision makers in this largely manual and iterative endeavor, we propose the design of a computer-aided decision tool which first automatically organizes urban shapes over a given empty territory, and then offer interactive manipulators that allow the experts to modify the spatial organization, while maintaining relations between shapes and informing experts of the impact of their choices. We cast the problem as a Local Search optimization in which we perform a sequence of swaps between urban shapes, starting from a random initial assignment. We extend the algorithm with novel heuristics to improve computational costs and propose an efficient distributed version. The same algorithm is used for the automated and interactive stages of the design process. The benefits of our approach are highlighted by examples and feedbacks from experts in the domain

Learning and memory of cue-reward association meaning by modifications of synaptic efficacy in dentate gyrus and piriform cortex

International audienc

Early polysynaptic potentiation recorded in the dentate gyrus during an associative learning task

International audienceIn this report, we investigated the electrophysiological dynamics of the neuronal circuit including the dentate gyrus during an associative task. A group of rats was trained to discriminate between a patterned electrical stimulation of the lateral olfactory tract, used as an artificial cue associated with a water reward, and a natural odor associated with a light flash. Polysynaptic field potential responses, evoked by a single electrical stimulation of the same lateral olfactory tract electrode, were recorded in the molecular layer of the ipsilateral dentate gyrus prior to and just after each training session. An increase in this response was observed when a significant discrimination of the two cues began. A positive correlation was found between the change in the polysynaptic potentiation and behavioral performances. The onset latency of the potentiated polysynaptic response was 35-45 ms. When a group of naive animals was pseudoconditioned, no change in field potential was observed. These results are consistent with the hypothesized dynamic activation of the dentate gyrus early in the making of association, allowing gradual storage of associative information in a defined set of synapses. Moreover, the onset latency of the potentiated response suggests the existence of reactivating hippocampal loops during the processing of associative information

Vestibular Modulation of Long-Term Potentiation and NMDA Receptor Expression in the Hippocampus

International audienc

EXTRACELLULAR RECORDINGS OF RODENTS IN VIVO : THEIR CONTRIBUTION TO INTEGRATIVE NEUROSCIENCE

International audienc