[Regulation of neural circuit function in the axon initial segment].

The axon initial segment (AIS) is a highly specialized neuronal subregion that separates axonal and somatodendritic compartments. The AIS is enriched with voltage-gated Na+ channels, and plays a critical role in determining neuronal activity. Recently, our understanding of AIS has seen major advances. Types and density of ion channels within the AIS vary among different neuronal types, which may underlie the variations in firing of neurons in the brain. Distribution of the AIS itself is not uniform among neurons either; rather, it is delicately determined in each neuron to meet its specific need. Furthermore, the AIS has a capacity for plasticity and reorganizes its distribution to regulate neural activity. In this review, I will show how these newly found features of AIS contribute to shape the function of neural circuits that are involved in the integration of binaural timing information for sound localization in birds.