PT - JOURNAL ARTICLE AU - Maria Teleńczuk AU - Romain Brette AU - Alain Destexhe AU - Bartosz Teleńczuk TI - Contribution of the Axon Initial Segment to Action Potentials Recorded Extracellularly AID - 10.1523/ENEURO.0068-18.2018 DP - 2018 May 21 TA - eneuro PG - ENEURO.0068-18.2018 4099 - http://www.eneuro.org/content/early/2018/05/21/ENEURO.0068-18.2018.short 4100 - http://www.eneuro.org/content/early/2018/05/21/ENEURO.0068-18.2018.full AB - 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.Signficance Statement Action potentials in most neurons initiate in the axon initial segment (AIS). However, the AIS is often neglected in computational studies. We studied the consequences of this initiation mechanism on the extracellular signatures of action potentials. We show that at the time of AP initiation AIS forms a dipole with the soma. The peak-to-peak amplitude of the extracellular action potential (EAP) generated by this dipole changes little with changing soma–AIS distance while the width of the EAP increases with the soma–AIS distance. This may help to monitor dynamic changes in the soma–AIS distance in experimental in vivo recordings.