Active properties of neocortical pyramidal neuron dendrites

Dendrites are the main recipients of synaptic inputs and are important sites determining neurons input-output functions. This review focuses on thin neocortical dendrites, which receive the vast majority of synaptic inputs in cortex but also have specialized electrogenic properties. We present a simplified working model biophysical scheme of pyramidal neurons that attempts to capture the essence of their dendritic function, including the ability to behave under plausible conditions as dynamic computational sub-units. We emphasize the electrogenic capabilities of NMDA receptors (NMDA-Rs), as these transmitter-gated channels seem to provide the major nonlinear depolarizing drive in thin dendrites, even allowing full-blown NMDA spikes. We show how apparent discrepancies in experimental findings can be reconciled and discuss the current status of dendritic spikes in vivo; a dominant NMDA-R contribution would mean the input-output relations of thin dendrites are dynamically set by network activity, and cannot be fully predicted by purely reductionist approaches