Cerebellar cortical circuitry provides one of the best understood neural circuits within the brain in terms of connectivity, the orderliness and characteristic geometry of this circuit inspiring the concept that the cerebellar cortex is a "neuronal machine". Surprisingly however, little has been done to reveal how this machine works in transforming input to Purkinje cell output: to understand cerebellar cortical function the relationship between input and output and how it is shaped by the activity patterns of cortical interneurons needs to be known. One problem is the identification of these interneurons in in vivo preparations where activity can be assessed. Here I will present some recent data on how different types of interneurones behave and may contribute to information processing.

Many studies of cerebellar interneurones have sought precise focal receptive fields, which might be related to some specific aspect of movement. Our findings however indicate that many cerebellar neurones integrate multi-sensory information from several modalities and areas of the body. For example, Golgi cells are major contributors to information processing, controlling transmission from granule cells to Purkinje cells. The multi-sensory responses of Golgi cells indicate that they are unlikely to play the 'gain control' role usually assumed on the basis of connectivity, but may be important for context dependent mossy fibre-parallel fibre transmission.