Date : 05/05/2011
Internship proposal for : Master 2
IBENS UMR CNRS 8197 et INSERM 1024
46 rue d'Ulm
Main discipline: Neurophysiology
Lab Director : Antoine Triller
Summary of lab's interests
Recently, the development of new experimental approaches allowing for simultaneous recording of many individual neurons in the living animal has lead to increasing interest in the dynamical coordination between the activities of cells in neural network. It is expected that the precise temporal organization of brain activity, such as the synchrony of discharge of hundreds or thousands of individual neurons, could be closely related to the coding and storing mechanisms used to represent information in the central nervous system. The work in our group participates to the study of this spatio-temporal organization of brain activity, and aims at a better understanding of the rules that governs encoding processes. Experimental approaches on behaving rats include multi-electrode recordings and, on anaesthetized rats, intra-cellular recordings and fast two-photon microscopy.
Summary of project
Rodents possess a set of macro-whiskers on their face, which are used in various behavioral tasks such as the localization of objects and the determination of their shape and texture. Tactile information obtained from the deflection of whiskers contacted by objects are represented in the somato-sensory cortex S1 within the S1bf area. Thalamic inputs are projecting in the layer 4 of S1bf, where neurons are organized in domains referred as barrels. There is a one to one correspondence between barrels and whiskers. The receptive fields of S1bf neurons are mainly centered on the principal whisker associate to this barrel. However, it has been shown recently that these receptive fields could have complex structures, spanning several adjacent whiskers and being dependant on the direction of the whisker deflection. The use of multi-whisker stimulators has moreover shown that the firing of a number of neurons was strongly modulated in presence of strong correlations between the deflection angles of adjacent whiskers. Some neurons detect the coherent motion of all whiskers, whereas others detect angular contrasts of deflection between the principal and adjacent whiskers (« center / surround » contrast).
We will study in this project if the tactile information contained in the spatio-temporal correlations between the deflections of the rat whiskers are represented also in the temporal correlations of the firing of layer 2/3 neurons. In this purpose, we will measure simultaneously the unitary activity of large neuronal populations in layer 2/3 during the presentation of stimulations with « center / surround » contrasts and in presence of background noise. We will study whether the stimulus features are encoded by an increase in the temporal correlations of the neuronal discharges.
Neuronal activities will be measured by two-photon calcium imaging in barrel cortex layer 2/3 of anaesthetized rats. Controlled stimulations will be applied with a multi-whisker stimulator built by the group of Daniel Shulz (UNIC, Gif / Yvette). This stimulator was recently implemented in our two- photon microscope setup. The measurement accuracy of the temporal correlations of neuronal activity will be analyzed and optimized by different scanning strategies in two photon microscopy.