Mossy fibre signals to the cerebellar cortex are received by granule cells, where the integration of synaptic inputs is necessary for the generation of output spikes. By performing whole-cell patch clamp recordings in the cerebella of anaesthetised rats, it has been possible to investigate the factors that contribute to granule cell synaptic integration in vivo. Despite receiving ongoing mossy fibre synaptic activity, resting granule cell firing rates are kept low. In particular, a shunting inhibition, in addition to hyperpolarisation, produced by tonic activation of GABA_A-receptors, are extremely important in maintaining a reduced granule cell excitability, and preventing the transformation of single mossy fibre inputs into granule cell action potentials. The resulting low firing rates act to increase the signal-to-noise ratio in the representation of sensory-evoked activity by the granule cell layer by rejecting spontaneous mossy fibre inputs, thus aiding the discrimination of sensory representations within the cerebellar cortex.