Lisa Roux / PhD seminar series – April 2018

Stabilization of the hippocampal map during spatial learning

April 6, 2018 – 11:30 (Amphi Broca Nouvelle-Aquitaine)
PhD , team leader: Olfaction and Memory / IINS
Invitant : Bordeaux Neurocampus / NBA

Abstract :

The formation of episodic and spatial memories requires a two-stage process that includes an “online” encoding phase, during which the memory trace is initially labile and vulnerable to interference, followed by an “offline” consolidation phase. Stabilization of the memory trace is thought to rely on reactivations of hippocampal networks, which would facilitate the progressive strengthening of the connections that represent the original experience. Reactivations are mainly coordinated by network events called sharp wave ripple oscillations (SPW-Rs) which occur during slow wave sleep, rest and consummatory behaviors. Rodent studies showed that during SPW-Rs, neurons coding for specific locations in space (“place cells”) replay previous waking activity patterns, corresponding to entire spatial trajectories. We hypothesized that activity during SPW-Rs mediates the stabilization of the hippocampal network during learning. We reasoned that if SPW-Rs are necessary for the network stabilization, disrupting neuronal activity specifically during those events would result in an altered mental representation of space coded by hippocampal place cells (the “cognitive map”).

Mice performed a spatial memory task requiring daily learning of three goal locations (hidden rewards) on a familiar multi-well maze. SPW-Rs occurred regularly during reward consumption. We used online position tracking, high-density extracellular recordings and closed-loop manipulations to trigger optogenetic silencing of a subset of CA1 pyramidal neurons, selectively during SPW-Rs at goal locations.

Control place cells (non-silenced or silenced outside SPW-Rs) largely maintained the location of their place fields after learning and showed increased spatial information content. In contrast, the place fields of SPW-R-silenced place cells remapped, and their spatial information remained unaltered. SPW-R silencing did not impact the firing rates or the proportions of place cells. These results suggest that interference with SPW-R-associated activity during learning prevents the stabilization and refinement of the hippocampal map.

Selected publications

Roux L., Hu B., Eichler R., Stark E., Buzsáki G. Sharp wave ripples during learning stabilize the hippocampal spatial map. Nature Neuroscience, 20(6):845-853 (2017)

Stark E., Roux L., Eichler R., Buzsáki G. Local generation of multi-neuronal spike sequences in the hippocampal CA1 region. Proc Natl Acad Sci U S A., 112(33):10521-6 (2015)

Roux L., Madar A., Lacroix MM, Chenju Y., Benchenane K., Giaume C. Astroglial Connexin 43 Hemichannels Modulate Olfactory Bulb Slow Oscillations. J Neurosci., 35(46):15339-52 (2015)

Stark E.*, Roux L.*, Eichler R.*, Senzai Y., Royer S., Buzsáki G. (*equal contribution) Pyramidal cell-interneuron interactions underlie hippocampal ripple oscillations. Neuron, 83(2):467-80 (2014)

Stark E., Eichler R., Roux L., Fujisawa S., Rotstein HG, Buzsáki G. Inhibition-induced theta resonance in cortical circuits. Neuron, 80(5):1263-76 (2013)

Roux L., Benchenane K., Rothstein J., Bovento G., Giaume C. Plasticity of astroglial networks in the olfactory glomeruli. Proc Natl Acad Sci U S A., 108(45):18442-6 (2011)

Scientific focus

Current research focus
The ability to store and retrieve associations between specific sensory stimuli and behaviorally relevant information is a vital memory function: it allows the organism to adapt its behavior based on prior experience. Olfaction is a central sensory modality in rodents as it supports an array of crucial behaviors such as predator avoidance, feeding, reproduction, maternal behavior and social interactions. Although specific odors can trigger innate responses, most odor stimuli acquire behavioral significance upon learning and experience. The goal of our team is to identify the network mechanisms underlying the formation of olfactory memory traces across distributed brain regions. More generally, we aim at understanding how sensory information is routed and processed in the brain to integrate lasting memories. To address these questions, we use a combination of advanced methods that allow monitoring and manipulating in real-time neuronal ensembles in freely moving animals towards a deep mechanistic understanding of brain functions. These methods include chronic multi-site high-density silicon probe recordings (units and local field potentials), 3D behavioral tracking, optogenetic tagging and closed-loop optogenetic manipulations in behaving rodents. Our work is funded by the Conseil Régional de la Nouvelle Aquitaine (Neurocampus project), the Initiative of Excellence of Bordeaux University (2017 Bordeaux Junior Chairs Program) and the ATIP-Avenir Program.

Short bio

2018 – Lisa Roux/ Group Leader: Olfaction and Memory Interdisciplinary Institute for Neuroscience (D. CHOQUET) CNRS UMR 5297, Bordeaux University, Bordeaux, France

2012 – 2017 : postdoctoral training / Buzsáki Laboratory NYU Medical School, Neuroscience Institute, New York, U.S.A. Topic: Mechanism and function of hippocampal sharp wave ripples

2006 – 2011 : Master 2 and Ph.D. Junctional communication and interactions between neuronal and astroglial networks (C. GIAUME) CIRB, Collège de France, Paris, France/ Topic: Neuroglial network interactions in the olfactory glomeruli

MAIN RESEARCH INTERESTS/ Systems neuroscience, Circuits’ function, Oscillations and synchrony, Inhibition Memory Plasticity .

Lisa Roux / Team Leader – Team Olfaction & Memory /

 

28/03/18