Contribution of the axon initial segment to action
potentials recorded extracellularly
Maria Telenczuk, Romain Brette, Alain Destexhe and Bartosz
eNeuro 5: 0068-18, 2018.
Action potentials (APs) are electric phenomena that are recorded
both intracellularly and extracellularly. APs are usually initiated
in the short segment of the axon called the axon initial segment
(AIS). It was recently proposed that at onset of an AP the soma and
the AIS form a dipole. We study the extracellular signature (the
extracellular action potential, EAP) generated by such a dipole.
First, we demonstrate the formation of the dipole and its
extracellular signature in detailed morphological models of a
reconstructed pyramidal neuron. Then, we study the EAP waveform and
its spatial dependence in models with axonal AP initiation and
contrast it with the EAP obtained in models with somatic AP
initiation. We show that in the models with axonal AP initiation
the dipole forms between somatodendritic compartments and the AIS,
and not between soma and dendrites as in the classical models.
Soma-dendrites dipole is present only in models with somatic AP
initiation. Our study has consequences for interpreting
extracellular recordings of single-neuron activity and determining
electrophysiological neuron types, but also for better
understanding the origins of the high-frequency macroscopic
extracellular potential recorded in the brain.
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