The location of the axon initial segment affects the bandwidth of spike initiation dynamics
Fig 1
Linear dynamical transfer properties of multicompartmental model neurons. We studied the dynamics of AP initiation in neuronal models, by estimating the temporal modulation of the instantaneous firing probability, in response to the somatic injection of a noisy current (B, green trace). The offset of this current (A-B, dashed grey trace) was weakly modulated over time at a harmonic frequency f. With Circular Statistics methods, we referred the time of each AP to the corresponding phase of the input oscillation. Then we regarded in the complex plane each AP as a vector with unitary length (C, filled colored markers) (C). We finally estimated the magnitude and phase of the vector sum (C), averaging together tens of thousands of APs and thus resulting in a vector with length lower than 1. We systematically explored magnitude and phase for a broad range of values of f (i.e. 10–1000 cycle/s). As the soma-AIS distance increased, the somatic AP waveform varied and became steeper (D).