Periodic Reporting for period 1 - DeepPop (Multimodal integration and population dynamics in the Deep Cerebellar Nuclei)
Reporting period: 2022-01-17 to 2024-01-16
• What is the problem/issue being addressed?
The cerebellum is a key structure involved in voluntary movement, motor learning and cognition. Understanding day-to-day fine motor coordination, but also how cerebellar dysfunctions can cause such a large spectrum of diseases (ataxia, dystonia, tremor, and some forms of autism and schizophrenia), requires us to decipher how information is processed within this structure. The cerebellum is made of a large cortical section, the well-studied cerebellar cortex, that performs extraordinarily complex sensorimotor processing, and a set of tiny neuronal nuclei, whose function is less well understood: the Cerebellar Nuclei (CN). Once computed in the cerebellar cortex, the cortical output is channelled through these small CN, which are the actual output of the cerebellum. How information is transformed after this computational funnel is unclear.
Recent advances have shown that the CN are composed of multiple subpopulations of neurons, that may be specialized in the control of distinct behaviours, although it is not clear which ones. Anatomical and experimental evidence also suggest that some of the inputs originating from outside the cerebellum (mossy fibres and climbing fibres) can directly influence the CN, indicating that the CN are more than just a relay. Understanding the properties of these inputs, and if and how they affect specific subpopulations in the CN is key to understand what processing happens during this last step of the cerebellar computations. This ultimately determines how the cerebellum controls other brain regions.
• Why is it important for society?
Fundamental research impacts society by deepening our understanding of how the brain works. Brain structures like the cerebellum are highly conserved across species, and many of the observation can be used to increase our understanding of the human brain. Besides increasing our understanding of the world, describing the functioning and network organization of a major brain structure like the cerebellum has potential medical and technological applications. It can lead to novel therapies for pathologies that are due to cerebellar disfunctions (ataxia, tremors), but also to other brain pathologies or disorders that have been shown to involve the cerebellum as part of bigger brain circuits, such as schizophrenia or autism. It can also have technological applications since some AI or robotic technologies are inspired by the cerebellar system.
• What are the overall objectives?
The main objective of this project was to improve our understanding of the processing rules in the cerebellar nuclei, by looking at how individual cells respond to different type of extracerebellar inputs, how they integrate different sources of information at the dendritic level, and how they process information at the level of the neuronal network.
The cerebellum is a key structure involved in voluntary movement, motor learning and cognition. Understanding day-to-day fine motor coordination, but also how cerebellar dysfunctions can cause such a large spectrum of diseases (ataxia, dystonia, tremor, and some forms of autism and schizophrenia), requires us to decipher how information is processed within this structure. The cerebellum is made of a large cortical section, the well-studied cerebellar cortex, that performs extraordinarily complex sensorimotor processing, and a set of tiny neuronal nuclei, whose function is less well understood: the Cerebellar Nuclei (CN). Once computed in the cerebellar cortex, the cortical output is channelled through these small CN, which are the actual output of the cerebellum. How information is transformed after this computational funnel is unclear.
Recent advances have shown that the CN are composed of multiple subpopulations of neurons, that may be specialized in the control of distinct behaviours, although it is not clear which ones. Anatomical and experimental evidence also suggest that some of the inputs originating from outside the cerebellum (mossy fibres and climbing fibres) can directly influence the CN, indicating that the CN are more than just a relay. Understanding the properties of these inputs, and if and how they affect specific subpopulations in the CN is key to understand what processing happens during this last step of the cerebellar computations. This ultimately determines how the cerebellum controls other brain regions.
• Why is it important for society?
Fundamental research impacts society by deepening our understanding of how the brain works. Brain structures like the cerebellum are highly conserved across species, and many of the observation can be used to increase our understanding of the human brain. Besides increasing our understanding of the world, describing the functioning and network organization of a major brain structure like the cerebellum has potential medical and technological applications. It can lead to novel therapies for pathologies that are due to cerebellar disfunctions (ataxia, tremors), but also to other brain pathologies or disorders that have been shown to involve the cerebellum as part of bigger brain circuits, such as schizophrenia or autism. It can also have technological applications since some AI or robotic technologies are inspired by the cerebellar system.
• What are the overall objectives?
The main objective of this project was to improve our understanding of the processing rules in the cerebellar nuclei, by looking at how individual cells respond to different type of extracerebellar inputs, how they integrate different sources of information at the dendritic level, and how they process information at the level of the neuronal network.
The experiments realized during the reporting period focused on the physiology of the extracerebellar inputs onto the CN neurons, in vitro. A first part focused on the anatomy, by targeting specific precerebellar nuclei to label origin-specific subgroups of mossy fibres and identify their targets in the CN. This was done using new viral approaches, which enabled the labelling of cerebellar nuclei neurons specifically targeted by the injected fibres, in a reporter mouse. This set of experiments resulted in an excellent transsynaptic labelling of cerebellar nuclei subpopulations. However, these experiments also revealed that the AAV construction used was not appropriate for the upcoming optogenetic experiments due to excessive toxicity on the presynaptic neurons. To solve this issue, virus expression levels were reduced, and a new batch of customized AAVs with lower toxicity, which are currently being generated and should enable higher quality experiments. A second set of experiments focused on the electrophysiological properties of the inputs, and in particular short term plasticities of excitatory extracerebellar synapses. Pilot experiments revealed a larger than expected diversity of short-term plasticity profiles in these inputs. Knowing whether these properties are origin-specific or target-specific will be determined in the near future. Finally, at the network scale, the existence and structure of local excitatory and inhibitory networks within the CN was tested, using glutamate uncaging mapping experiments. For now, these early results give some interesting insight on the network organization but have mostly been discussed and presented internally for scrutiny during lab meetings. Our plans for future dissemination and exploitation include additional presentations at scientific meetings to gain critical feedback before publication of the results
Data collected during the initial stages of DeepPop enabled the preparation a more ambitious project that was awarded by an ERC-starting grant in 2021, CereCode. This 9-month reporting period of DeepPop enabled to set up and calibrate most of the equipment required for studying the CN and optimize the methodology for the upcoming experiments in vitro and in vivo. It helped refining the technological needs in terms of imaging capacities, and in particular in term of acousto-optic lens imaging for future experiments. This helped make some technological choices and validated some of the viral approaches that were proposed for the project. While many of the observations made are still preliminary, some very interesting observations have been made in terms of cerebellar physiology, although they will need further confirmation in the coming year through the upcoming ERC project CereCode.