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Laurent Bourdieu

Cortical Dynamics and Sensory Mechanisms

Context


The study of neural activity across tens to thousands of cells is a rapidly developing field, particularly through advances in two-photon microscopy. The goal of the team led by Laurent Bourdieu is to study the spatial and temporal organization of brain activity at the level of local neural networks and to understand some rules governing sensory information encoding in the rodent cortex. These issues are mainly addressed using two-photon microscopy, a technique that the team is constantly trying to improve in terms of temporal resolution, sensitivity and penetration depth.

Research highlights


In the past few years, the team has studied coding of sensory information in the rat cortex. In particular, the functional organization of somatosensory cortex, in which the movement of whiskers is encoded, was explored. Whiskers are major tactile organs allowing rodents to explore their environment and textures. Whiskers are represented in the cortex in columns called "barrels". All neurons of a given barrel preferentially respond to the stimulation of a single whisker. The team described the functional organization of neurons within a barrel column based on their selectivity for the direction of the whisker stimulation (called preferred direction). Ending a controversy, it demonstrated that a map of preferred directions emerges very late during development and could be linked to the longest sensory experience of adult rats. Currently, the team is interested in the representation of coordinated movements of whiskers, highlighting the presence and functional organization in the supragranular layers of cells selective to either correlated movements of whiskers or to anti-correlated movements (detecting contrasts).

The team also aims at improving optical imaging methods, particularly two-photon microscopy. This technique allows in vivo measurements of neuronal activity (by recording individual action potentials) and of the spatial organization of small local networks, while enabling identification of certain cell types and their projections to neighboring regions. In collaboration with Stéphane Dieudonné’s team, Laurent Bourdieu’s group designed an ultrafast random access scanner for two-photon microscopy. The scanner is based on acousto-optic deflectors and allows access to temporal resolutions of the order of a millisecond. This work is ongoing with the development of a high-speed 3D scanner. In order to increase the imaging depth into the tissue, the researchers also developed adaptive optics strategies. In particular, they designed a system to measure the laser wavefront in the tissue by interferometric selection of back-scattered photons, a technique having many similarities with optical coherence tomography (OCT). The team is also interested in developing fiberscopes to image freely behaving rodents and study the coding of neuronal activity during complex behavioral tasks.

Focusing ligth through dynamical samples using fast continuous wavefront optimization
B. Blochet, L. Bourdieu, S. Gigan, Optics Letters, 2017, in press.

A radial map of multi-whisker correlation selectivity in the rat barrel cortex
L. Estebanez, J. Bertherat, D. E. Shulz, L. Bourdieu, J.-F. Léger
Nat Commun. 2016;7:13528. doi: 10.1038/ncomms13528.

Fast spatial beam shaping by acousto-optic diffraction for 3D non-linear microscopy.
W. Akemann, J.-F. Léger, C. Ventalon, B. Mathieu, S. Dieudonné, L. Bourdieu
Opt. Exp. 2015(22); 23:28191-28205

Characterization of the angular memory effect of scattered light in biological tissues.
S. Schott, J. Bertolotti, J.F. Léger, L. Bourdieu, S. Gigan,
Opt. Exp. 2015(10); 23:13505-13516

Spatially Selective Holographic Photoactivation and Functional Fluorescence Imaging in Freely Behaving Mice with a Fiberscope.
V. Szabo*, C. Ventalon*, V. De Sars, J. Bradley, V. Emiliani,
Neuron. 2014; 84(6):1157–1169

Late emergence of the vibrissa direction selectivity map in the rat barrel cortex.
Kremer Y, Léger JF, Goodman D, Brette R, Bourdieu L.
J Neurosci. 2011; 31(29):10689-700.




Direction selectivity map in the rat barrel cortex
Direction selectivity map in the rat barrel cortex