Spikelets in Pyramidal Neurons: Action Potentials Initiated in the Axon Initial Segment That Do Not Activate the Soma
Fig 6
Orthodromic spikelets evoked with somatic background inputs and dendritic current stimuli.
A: Neuron model with fluctuating somatic inputs as in Fig 1 (red: excitatory, blue: inhibitory). Additionally, the model cell was stimulated every 20 ms with a brief current pulse at the proximal apical dendrite (orange, see Methods). B: Left: example somatic spikelets; shown are 15 spikelets evoked with the dendritic stimulus (orange) and 15 spikelets evoked with the somatic background stimulus (black). Right: phase plots of the depicted spikelets. C: Spikelet-triggered averages for all spikelets evoked with the somatic background stimulus (N = 41, dashed lines) and all spikelets triggered by the dendritic input (N = 43, dotted lines) generated within 200 s of simulation, see Methods. C1: Mean spikelets evoked with the somatic background stimulus (black dashed line) and with the dendritic stimulus (orange dotted line), aligned to the voltage-threshold crossing at the AIS (as in Fig 1H). C2: Mean excitatory (red) and inhibitory (blue) conductances for spikelets evoked with the somatic background stimulus (dashed lines) and for spikelets evoked with the dendritic stimulus (dotted lines). C3: Mean effective synaptic reversal potentials (as in Fig 1H) for spikelets evoked with the somatic background stimulus (dashed line) and with the dendritic stimulus (dotted line).