The PhD defense of Selma Souihel (Biovision Lab) will take place on Wednesday, December 18th at 15:00, in the Amphitheater Morgenstern, Kahn Building, at Inria Sophia Antipolis. The presentation will be in English. You are also welcome to attend the reception that will take place after the defense.
Title : “Generic and specific computational principles for integration of motion trajectories”
English Abstract :
Vision is initiated in the retina, where light is converted into electrical signals by photoreceptors, sent to bipolar cells then ganglion cells, generating spike trains. Visual information is then transmitted to the thalamus via the optic nerve which in turn transmits it to the visual cortex. The retinal processing alone takes time, up to 150 ms, not to mention the time lags introduced by synaptic transmissions between the three processing units. This shows that the existence of compensatory mechanisms to reduce processing delays is absolutely essential. These compensatory mechanisms are known as anticipation.
Anticipation first occurs at the level of the retina and is further carried out by the primary visual cortex. In its first occurrence, anticipation is either characterized by a shift in the peak response, or a short-range wave of activation. In the second case, it is characterized by a wider range wave of activation.
The first contribution of this thesis is the development of a generalized 2D model of the retina, mimicking three types of ganglion cells: Fast OFF cells with gain control, direction-selective cells with gap junction connectivity, and differential motion cells connected through an upstream amacrine circuit, able of anticipating a different kind of moving stimuli.
The second contribution is to use our retina model as an input to a mean-field cortical model to reproduce motion anticipation as observed in voltage-sensitive dye imaging recordings. Throughout our work, we will study the effect of non-linear phenomena involved in anticipation, as well as connectivity, both at the level of the retina and the primary visual cortex. The integrated retino–cortical model allowed us to study the effects of anticipation on two-dimensional stimuli, and to highlight the collaborative aspect of anticipation in the retina and the cortex.
The third contribution is the development of a method to compute correlations between spike trains in the non-stationary case, which we applied to experimental data from salamander and mice retina. We found a variation in correlations during movement, which could be related to interactions between cells. These interactions suggest that the motion of an object can be extrapolated, not only through firing rates but also by the spike train correlations that reflect the spatio-temporal correlations in its trajectory.
Jury :
Supervisor :
Dr. Bruno Cessac, Inria Sophia Antipolis
Reviewers
Dr. Laurent Perrinet, Université Aix Marseille
Dr. Matthias Hennig, University of Edinburgh
Dr. Michael J. Berry II, Princeton University
Examiners
Dr. Frédéric Chavane, Université Aix Marseille
Dr. Olivier Marre, Institut de la Vision
Dr. Stephanie Palmer, University of Chicago
Dr. Benoit Miramond, Université Côte d’Azur
