Spikelets in Pyramidal Neurons: Action Potentials Initiated in the Axon Initial Segment That Do Not Activate the Soma
Fig 4
Orthodromic and antidromic spikelets in the biophysically complex model.
A: Neuron model with fluctuating somatic inputs as in Fig 1 (red: excitatory, blue: inhibitory). Additionally, the model cell was stimulated every 500 ms with a short current pulse at the distal axon (orange, see Methods). B: Left: example somatic spikelets; shown are 20 orthodromic (black, evoked with somatic inputs) and 20 antidromic spikelets (orange, evoked with distal axonal inputs). Right: phase plots of the spikelets depicted in the left panel. C: Spikelet-triggered averages for all orthodromic spikelets (N = 66, dashed lines) and all antidromic spikelets (N = 194, dotted lines) generated within 100 s of simulation. C1: Mean orthodromic (dashed black) and antidromic (dotted orange) spikelet, aligned to the voltage-threshold crossing at the AIS (as in Fig 1H). C2: Mean excitatory (red) and inhibitory (blue) conductances for orthodromic (dashed lines) and antidromic (dotted lines) spikelets. C3: Mean effective synaptic reversal potentials (as in Fig 1H) for the orthodromic (dashed line) and antidromic (dotted line) spikelets.