  Since the first experimental evidences of active conductances in dendrites,
most neurons have been shown to exhibit dendritic excitability through the
expression of a variety of voltage-gated ion channels. However, despite
experimental and theoretical efforts undertaken in the last decades, the role
of this excitability for some kind of dendritic computation has remained
elusive. Here we show that, owing to very general properties of excitable
media, the average output of a model of active dendritic trees is a highly
non-linear function of their afferent rate, attaining extremely large dynamic
ranges (above 50 dB). Moreover, the model yields double-sigmoid response
functions as experimentally observed in retinal ganglion cells. We claim that
enhancement of dynamic range is the primary functional role of active dendritic
conductances. We predict that neurons with larger dendritic trees should have
larger dynamic range and that blocking of active conductances should lead to a
decrease of dynamic range.
