Information processing in a cerebellar granule cell

A fifteen compartment, biologically realistic model of a cerebellar granule cell (GC) was developed to examine the signal processing capabilities of this most numerous element in the cerebellar cortical circuit. The model explicitly includes compartments for the soma, axon hillock, proximal axon, dendrites and terminal bulbs. All synaptic inputs were transduced via activation of glutamate receptor subtypes located on the dendritic bulb compartments, and were systematically varied in their number and frequency. An intriguing morphological feature, in which axonal location is shifted from the soma to a dendrite, was specifically examined to determine its impact on granule cell output. The GC was shown to be electrotonically compact, resulting in a lack of biasing of output based on axonal location. Biasing of output could be driven by changes in the passive parameters of the model, but required an unrealistically large change in resistive coupling between dendritic and somal compartments. Thus, axonal location does not induce physiologically relevant phase shifts between synaptic inputs located on multiple dendritic bulbs, suggesting that the GC relies heavily upon temporal aspects of its input signals for integrative processing.