Specific wiring rules implicate diverse temporal processing within cerebellar microcircuits – NetOnTime

The cerebellum plays a major role in the control, timing and learning of skilled movements. The cerebellar cortex combines multimodal sensorimotor information conveyed by mossy fiber (MF) inputs with internal models of the motor apparatus to precisely time cerebellar output. Our goal is to understand how temporal computations are performed in cerebellar circuits. The cerebellar cortex is organized as an array of repeated modules that process information in parallel. However, many studies have demonstrated that individual modules present anatomical and functional regional differences leading to a large diversity of information processing among them. Therefore, an exhaustive functional description of cerebellar modules is necessary to understand how they use intrinsic timing mechanisms across modules to coordinate behavior. Also, the computational power of the cerebellum to learn different patterns of multi-sensory contexts relies on the ability to integrate information streams within modules. Therefore, how does the cerebellum combine both contextual mixing and specific modular organization to control movements? We hypothesize that loose compartmentalization of MF information within cerebellar cortex circumvents the limitations of an all-to-all wiring and enables generalization and robustness, while preserving pattern separation and computational power for specific tasks. Our main questions are:
-How does the circuit connectome determine functional coupling between cerebellar modules? In particular, since granule cells (GCs) at a given location are developmentally clonally related, could cell lineage patterns be responsible for generating functional cerebellar modules?
-How do cerebellar modules differentially process and coordinate temporal information in order to precisely drive movements in normal and altered conditions?
We propose to (1) establish the spatial organization of GC-induced excitatory and inhibitory inputs onto interneurons and Purkinje cells using glutamate uncaging in normal and altered conditions (Task 1). These spatial maps will be compared to GC clonal organization (Task 2), applying new methodologies based on combinations of fluorescence labels of distinct colors, and a new multiphoton color microscopy scheme optimal to image these markers at high resolution in intact neural tissue. In that context, functional synaptic properties of GC clones will be assessed. Then we will address how temporal properties in the MF-GC-Purkinje cell pathway are embedded in the modular organization (Task 3 and 4) using 2P microscopy and iGluSnFR imaging. We will examine whether pathway-specific MF synaptic dynamics also correlates with GC-Purkinje cell synaptic dynamics. We will also consider whether there might be module-specific properties, which may be tuned for specific temporal dynamics of the behaviors controlled by those modules. Then, we will examine whether GC clones exhibit similar synaptic dynamics. We will activate MF subtypes and monitor both E/I balance in the molecular layer and temporal coding strategies in individual GC clones, interneurons and Purkinje cells.. Using modelling (Task 4) we will test the computational effects of the spatio-temporal distribution of dynamic synapses along the MF-Purkinje cell pathways. Finally, we will monitor how modules adapt to behavioral perturbations and study operational rules of microzonal communication (Task 5). All these results will be included in a web platform for dissemination and sharing (Task 6).
This proposal is transformative because it will elucidate the synaptic and circuit mechanisms of cerebellar function. Specifically we will show how the CC uses simple rules to represent complex time-varying sensori-motor contexts within modules, and yet generate module-specific Purkinje cell output dynamics for specific actions. We expect that the temporal mechanisms identified here may provide insight into the building blocks of neural computations in other circuits.