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Synchrony among Neighbor Neurons in Cerebellum

Final Report Summary - SYNC (Synchrony among Neighbor Neurons in Cerebellum)

The project objectives :

The SYNC project aimed at investigating the role of synchronous activity in local neuronal networks of the Cerebellum in motor coordination and learning, and at understanding how such synchronous Purkinje cell activity can be decoded by the output structure of the Cerebellum: the Deep Cerebellar Nuclei (DCN). This has involved pioneering the development and use of novel optogenetic tools so that in the longer term, it will become possible to address questions such as: what is the transfer function between Purkinje cell population activity and DCN activity? How is it modified by motor learning or ongoing brain state? What are the underlying biophysical mechanisms? What are the constraints on cerebellar motor learning imposed by the functioning of this circuit, and can they be circumvented to enhance motor performance? How is the circuit affected in cerebellar pathologies, and what therapeutic approaches could be explored?

The optogenetic tools we developed allow the selective activation or inhibition of chosen subpopulations of Purkinje cells. This is achieved using patterned illumination of the cerebellar cortex in mice in which Purkinje cells are engineered to express light-sensitive ion channels (Channelrhodopsin) or pumps (Archeorhodopsin). The first application of these new tools is in establishing the functional connectivity map between Purkinje cells in lobule 5 of the cerebellar vermis (the optically most accessible part of the mouse cerebellum) and single target neurons in the Medial Nucleus of the DCN, the main downstream output nucleus for this lobule.

Work carried out at Stanford University (USA) and at the CNRS (France):

The following steps have been achieved during Dr. Piwkowska-Zvonkine’s stay at Stanford University in the United States, in the laboratory of Dr. Mark Schnitzer (Outgoing Host):
• The expression of opsins has been obtained specifically in Purkinje cells with a widespread, uniform distribution.
• An optical system for delivering patterned light to the brain tissue together with a user-friendly interface for controlling the stimuli has been built.
• Preliminary experiments combined photostimulation of Purkinje cells with simultaneous extracellular single unit recordings of both DCN neurons and Purkinje cells.

During the Return period of the Fellowship at the CNRS in France, in the laboratory of Dr. Yves Frégnac, subsequent steps achieved by the Fellow were:
• The development of Matlab applications for analyzing complex data combining electrophysiological signals, images of the brain, photostimulation patterns and timing.
• A refinement of the targeting of the Medial Nucleus, a small structure in the mouse, for extracellular recording, to increase the yield of our experiments.

These wide-ranging technical developments, spanning biotechnology, optics, hardware and software, led to a series of experiments performed in the Schnitzer lab which allowed the efficient collection of in vivo recordings from 30 individual DCN neurons receiving inputs from the Purkinje cell population under study. Analysis of this data is on-going and will shed light on the spatial organization of Purkinje cells converging onto a single downstream neuron and thus on the fine-scale network organization of the cerebellar circuitry.

Final results and their potential impact :

Our preliminary results support the idea that the wiring of the Purkinje-to-DCN projection is a key element of the transformation from a somatotopic representation space in the cerebellar cortex to a different representation space in the cerebellar output nuclei. Our technique is a first step in the development of fast-throughput optics-based tools for mapping functional brain connectivity in vivo, and our experiments will also be useful in guiding the future progress of such approaches.

The Fellow has gained new expertise in and contributed to the development of the newest generation of neurophysiological tools. She has established lasting scientific contacts with an outstanding center for the development of such tools at Stanford University, and has brought back to Europe this new technological capability, together with transgenic animals, experimental protocols and new analysis tools.

Following on from the Marie Curie fellowship, Zuzanna Piwkowska-Zvonkine has joined as a postdoctoral fellow a new team starting up at the Return Host institute, directed by Dr. Brice Bathellier who is recipient of a Marie Curie Career Integration Grant. The new research project directed by Dr. Brice Bathellier also receives funding from the French Agence Nationale de Recherche (ANR) and will make use of the new technology and analytical tools in a study of multi-sensory cortical processing.