Soutenance de thèse de Isabelle Racicot (Equipe NeOpTo)

Lundi 19 décembre à 14h, à l’amphithéâtre du Laboratoire d’Astrophysique de Marseille (à Château-Gombert)

Isabelle Racicot (Equipe NeOpTo)

Soutiendra sa thèse de doctorat intitulée:
Measuring unexplored fields of view in the non human primate’s visual cortex by advanced optical imaging

Lien visio
https://univ-amu-fr.zoom.us/j/3586639578

Jury: 
Isabelle Ferezou – Université Paris-Saclay (rapporteure)
Serge Meimon – Onéra(rapporteur)
Carole Deumié  – École Centrale Marseille & Institut Fresnel (Présidente du jury)
Dirk Jancke – Ruhr University Bochum (examinateur)
Marc Ferrari – Aix-Marseille université (co-superviseur)
Frédéric Chavane – Aix-Marseille université (superviseur)

Abstract :

Cortical activity can be recorded using a variety of tools, ranging in scale from the single neuron (microscopic) to the whole brain (macroscopic). There is usually a trade-off between scale and resolution; optical imaging techniques, with their high spatio temporal resolution and wide field of view, are the best suited to study brain activity at the mesoscale.

The maximum field of view that can be achieved with optical imaging of cortical areas is however in practice limited by the curvature of the brain, which causes the im- age quality to deteriorate significantly away from the center of the image. Harnessing the full potential of optical cortical imaging techniques therefore requires accounting for the brain curvature.

This thesis aims at addressing the brain curvature issue by building an imaging instrument adapted to optically image at large fields of view the visual cortex of the rhesus macaque. The components of the instrument include a curved CMOS detector, which, combined with an aspherical lens, accounts for the brain curvature of the macaque monkey. The instrument also includes an LED ring that provides uniform illumination on the cortical surface in four wavebands used with the main optical imaging techniques in neuroscience that include optical imaging of intrinsic signals and voltage-sensitive dye imaging.

The instrument was built through several iterations and, when characterized on an optical test bench, yielded a significant increase in the fraction of the area optically accessible that could be imaged in focus, from 28 % (70 mm2) with the standard imaging tool to over 100 % (302 mm2) with the new instrument. The instrument was used for in vivo imaging of a macaque visual cortex and made it possible to image a larger area of the visual cortex at a constant resolution. An algorithm developed to estimate the optical performance of an instrument from a single image containing sharp edges allowed to estimate the in vivo resolution. The results indicated a 4-fold increase in the evenness of the resolution in the field of view, suggesting that the curvature was well accounted for. An additional element consisting of a weak infrared laser and a small diffractive optical element was added to instrument in order to project a pattern on the cortex and measure the distortions of the surface caused by physiological effects like breathing and the heartbeat.

This new instrument, which is to the best of our knowledge the first use of a curved detector for cortical imaging, should facilitate the observation of wide mesoscale phenomena such as dynamic propagating waves within and between cortical maps, which are otherwise difficult to observe due to technical limitations of the currently available recording tools.