Biology subjects

Rouault, H.

Publications and source records attributed to Rouault, H..

5 recordsLinked to original sources

bioRxiv2025

Parallel emergence of perisomatic inhibition and ripples in the developing hippocampal circuit

During hippocampal Sharp Wave Ripples, sequences of awake coding activities are replayed with a rhythmic timing and high level of synchrony favorable for synaptic plasticity and transfer of information to downstream structures. Previous work reported the emergence of ripples at P10 in the CA1 region, together with the development of inhibition. On the other hand, neither the relationships between perisomatic inhibition and ripples nor their developmental emergence have been investigated in CA3, in which ripples have a different frequency profile (90-110Hz instead of 140-200Hz in CA1), functional perisomatic inhibitory circuits have different properties, and some developmental aspects such as neurogenesis or interneuron maturation are early compared to CA1. We have here investigated the hypothesis of a conjoint and earlier appearance and maturation of ripples and perisomatic inhibition in the CA3 hippocampal region compared to CA1. We report a parallel sequence of events in CA3 and CA1, starting with the early expression of perisomatic GABAergic synaptic activity combined with the emergence of ripple activity. Interestingly, perisomatic inhibition and ripple activity follow parallel maturation trajectories, beginning in CA3 at P7 with immature (i.e. not functional yet) inhibition and immature ripples (proto-ripples) with labile oscillatory frequency. Mature functional perisomatic inhibition and clear high-frequency ripple activity progressively emerge between P10 and P12, reaching adult-like properties by P13. A similarly progressive maturation of ripples occurs in CA1, from P11 to P15. The progressive emergence of functional inhibition and specific patterns of neuronal activity likely support the progressive emergence of cognitive function to which they are necessary prerequisite.

neuroscience↗

bioRxiv2024

An Independent Coding Scheme for Distance versus Position in the Hippocampus

Animals navigate using cognitive maps of their environment, integrating external landmarks and distances between them. Hippocampal place cells are the neuronal substrate of these cognitive maps. However, while hippocampal allocentric position coding in reference to external landmarks is well characterized, the determinants of idiothetic hippocampal distance coding remain poorly understood. Using virtual reality, electrophysiological recordings in mice, and local cue manipulations we could dissociate distance from position coding. In the cue-poor condition, we found pervasive distance coding with high distance indices in all bidirectional place cells including both superficial and deep CA1 pyramidal cells. In this condition, the mapping of distance onto a low-dimensional manifold and rigid distance relationships between place fields suggested strong attractor dynamics similar to those observed for grid cells. Inactivation of the medial septum (MS), which disrupts grid cells, significantly reduced both distance coding and rigid distance dynamics, suggesting an alteration (but not complete abolition) of the underlying attractor. In contrast, allocentric position coding could be observed in cue-rich environments, predominantly engaged deep CA1 pyramidal cells, and persisted during MS inactivation. These results are consistent with a selective contribution of grid cells and associated rigid attractor dynamics to hippocampal idiothetic distance coding but not allocentric position coding.

neuroscience↗

bioRxiv2022

One engram two readouts: stimulus dynamics switch a learned behavior in Drosophila

Memory guides behavior across widely varying environments and must therefore be both sufficiently specific and general. A memory too specific will be useless in even a slightly different environment, while an overly general memory may lead to suboptimal choices. Animals successfully learn to both distinguish between very similar stimuli and generalize across cues. Rather than forming memories that strike a balance between specificity and generality, Drosophila can flexibly categorize a given stimulus into different groups depending on the options available. We asked how this flexibility manifests itself in the well-characterized learning and memory pathways of the fruit fly. We show that flexible categorization in neuronal activity as well as behavior depends on the order and identity of the perceived stimuli. Our results identify the neural correlates of flexible stimulus-categorization in the fruit fly. Impact StatementFlies can optimally recall a memory with high specificity by comparing options close in time, or default to generalization when they cannot.

neuroscience↗

bioRxiv2021

The rapid developmental rise of somatic inhibition disengages hippocampal dynamics from self-motion

Early electrophysiological brain oscillations recorded in preterm babies and newborn rodents are initially mostly ignited by bottom-up sensorimotor activity and only later can detach from external inputs. This is a hallmark of most developing brain areas including the hippocampus, which in the adult brain, functions in integrating external inputs onto internal dynamics. Such developmental disengagement from external inputs is likely a fundamental step for the proper development of cognitive internal models. Despite its importance, the developmental timeline and circuit basis for this disengagement remain unknown. To address this issue, we have investigated the daily evolution of CA1 dynamics and underlying circuits during the first two postnatal weeks of mouse development using two-photon calcium imaging in non-anesthetized pups. We show that the first postnatal week ends with an abrupt shift in the representation of self-motion in CA1. Indeed, most CA1 pyramidal cells switch from activated to inhibited by self-generated movements at the end of the first postnatal week whereas the majority of GABAergic neurons remain positively modulated throughout this period. This rapid switch occurs within two days and follows the rapid anatomical and functional surge of local somatic GABAergic innervation. The observed change in dynamics is consistent with a two-population model undergoing a strengthening of inhibition. We propose that this abrupt developmental transition inaugurates the emergence of internal cognitive models.

neuroscience↗

bioRxiv2019

Dynamic control of cortical head-direction signal by angular velocity

The sense of direction requires accurate tracking of head direction at different turning-velocities, yet it remains unclear how this is achieved in the mammalian brain. Here we recorded head-direction cells in bat dorsal presubiculum and found that, surprisingly, the head-direction signal in this cortical region was dynamically controlled by angular velocity. In most neurons, a sharp head-direction tuning emerged at some angular velocity, but was absent at other velocities - resulting in a 4-fold increase in head-direction cell abundance. The head-direction tuning changed as a function of angular velocity primarily via a redistribution of spikes between the neurons preferred and null directions - while keeping the average firing-rate constant. These results could not be explained by existing ring-attractor models of the head-direction system. We propose a novel recurrent network model that accounts for the observed dynamics of head-direction cells. This model predicts that the new classes of cells we found can improve the sensitivity of the head-direction system to directional sensory cues, and support angular-velocity integration.

neuroscience↗