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The cerebellar control of motor tuning during sensory discrimination

Final Report Summary - CBTOUCH (The cerebellar control of motor tuning during sensory discrimination.)

The sense of touch is used by animals to build a spatial representation of the surrounding environment. A large fraction of the tactile information is acquired in an active context, while the body is moving in space and brought into contact with the environment either incidentally or purposely. The nervous system must thus integrate sensory and motor inputs to optimize movements aimed at collecting information and correctly interpreting the sensations. A paradigmatic example of such sensorimotor coordination is to be found in the whisking behavior of rodents. A complex network controls the rodent's mobile vibrissae and processes the sensory information they collect. The cerebellum is one of the least characterized brain structure in this network. Yet, facial sensory information is provided to the cerebellum by direct projections from the trigeminal nucleus and by indirect projections from the sensory cortex via the pontine nucleus; cerebellar activity is synchronized with the sensory cortex during whisking; an intact cerebellar connection with the sensory cortex is necessary for vibrissae-guided behaviour. Moreover vibrissal movements have been shown to be modulated by an oscillatory signal arising in the olivo-cerebellar system. It remains to be understood how the cerebellum may contribute to sensorimotor integration in the vibrissae system.
A multi-technique approach was used to allow exploration of the cerebellar contribution to active sensory discrimination from different points of view. In a first stage, optical imaging of flavoprotein autofluorescence was used to identify the network components and their functional connectivity in anesthetized animals. Electrophysiological recordings with tetrodes in the identified area confirmed imaging data while allowing a more subtle investigation. All these results were complemented with anatomical studies of neuronal tracing.
Using these techniques we described for the first time a zone in the lateral part of the cerebellar Crus I lobule where primary sensory and motor cortical inputs converge at the cellular level. Moreover we demonstrated that this cerebellar zone of sensorimotor convergence projects back to the motor cortex thus forming functional cortico-cerebellar reciprocal loops.
In order to understand the functional role of these connections we performed high-speed videography of whiskers movement in head restrained mice after optogenetical stimulation of the cerebellar surface. We found that the lateral Crus I lobule contributes to tuning of whisking movements, notably in the fine adjustments regulating the contact with surrounding objects.
The subject of sensorimotor integration is very popular in the European context with many groups working hard to clarify the underlying cerebral network. The study in this field could have, indeed, a great potential clinical interest since an abnormal sensorimotor interplay has been demonstrated not only in case of direct insults or stroke in sensorimotor areas but also in speech disorders as well as Huntington and Parkinson diseases, schizophrenia or autism. To completely understand its role in pathology, however, a precise knowledge of the circuitry involved in sensorimotor cooperation is necessary. The CBTOUCH project has been designed to answer this question and to characterize in depth the reason why sensory and motor areas should maintain such an accurate communication during everyday life situations.