The cerebellum plays a crucial role in sensorimotor processing, yet little is known about its contribution towards sensory signal processing. The whisking behaviour in rodents is a model behaviour for sensorimotor function and the Crus I and II lob ules of the cerebellum have been shown to represent perioral stimulation, linearly encoded whisker setpoint and be important in the generation of whisker movement.

To target our investigation of the sensory representation, I have used a very nar rowly defined stimulus, the deflection of a single whisker, to investigate the re sponse in cerebellar cortex neurons using whole-cell and cell-attached patch-clamp.

In the first step of cerebellar cortex processing, I found the convergence in individual granule cell of mossy fibre inputs at latencies indicating a direct pathway through the trigeminal nuclei and a cortico-pontine path for the single whisker signal. Mo lecular layer interneurons were found to be highly precisely and rapidly excited by the early direct path input from granule cells. Lateral inhibition was also displayed by a molecular layer interneuron with an inhibitory response.

The sole output of the cerebellar cortex, the Purkinje cells, exhibited simple spike responses often combining excitatory and inhibitory phases in the majority of rec orded cells despite the narrowness of the stimulus and the wide recording location. A complex spike response was measured in half of the Purkinje cells with a simple 7 response and never in Purkinje cell without simple spike responses. This separation of the Purkinje cell population into neurons receiving both mossy fibre and climbing fibre input on the single whisker deflection and those that only receive mossy fibre input suggest different mechanisms (e.g. plasticity) and functions.

Together, these findings quantify the sensory input to the cerebellar cortex follow ing a single whisker deflection and the downstream processing of this signal.