Biology subjects

Lefort, J. M.

Publications and source records attributed to Lefort, J. M..

3 recordsLinked to original sources

bioRxiv2020

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 ones 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. While rats demonstrated knowledge of environmental connectivity, their place cells did not respond to connectivity changes, nor did they represent doorways differently from other locations. Importantly, place cells coded the space in a global frame, expressing minimal repetitive fields despite the repetitive geometry (global coding). These results suggest that CA1 place cells provide a spatial map that does not explicitly include connectivity.

neuroscience↗

bioRxiv2018

Dissociation of fear initiation and maintenance by breathing-driven prefrontal oscillations

Does the body play an active role in emotions? Since the original James/Cannon controversy this debate has mainly been fueled by introspective accounts of human experience. Here, we use the animal model to demonstrate a physiological mechanism for bodily feedback and its causal role in the stabilization of emotional states. We report that during fear-related freezing mice breathe at 4Hz and show, using probabilistic modelling, that optogenetic perturbation of this feedback specifically reduces freezing maintenance without impacting its initiation. This rhythm is transmitted by the olfactory bulb to the prefrontal cortex where it organizes neural firing and optogenetic probing of the circuit demonstrates frequency-specific tuning that maximizes prefrontal cortex responsivity at 4Hz, the breathing frequency during freezing. These results point to a brain-body-brain loop in which the initiation of emotional behavior engenders somatic changes which then feedback to the cortex to directly participate in sustaining emotional states.

neuroscience↗

bioRxiv2017

Harnessing sleep/wake state tracking by olfactory bulb oscillations to perform fully brain-based sleep scoring in mice

It has long been thought that sleep scoring could not be achieved with brain signals alone despite the deep neuromodulatory transformations that accompany sleep state changes. Here we demonstrate using multi-site electrophysiological LFP recordings in freely moving mice that gamma power in the olfactory bulb (OB) allows for clear classification of sleep and wake. Coupled with hippocampal theta activity, it allows the construction of a sleep scoring algorithm that relies on brain activity alone. This method reaches over 90% homology with classical methods based on muscular activity (EMG) and video tracking. Moreover, contrary to EMG, OB gamma power allows correct discrimination between sleep and immobility in ambiguous situations such as fear-related freezing. We use the instantaneous power of hippocampal theta oscillation and OB gamma oscillation to construct a 2D phase-space that is highly robust across mice and days. Dynamic analysis of trajectories within this space yields a novel characterization of sleep/wake and wake/sleep transitions as deeply divergent phenomena. Whereas waking up is a fast and direct transition, falling asleep is best described as stochastic and gradual change. Altogether this methodology opens the avenue for multi-timescale characterization of sleep states with high temporal resolution based on brain signals only.

neuroscience↗