An axon initial segment is required for temporal precision in action potential encoding by neuronal populations

Sci Adv. 2018 Nov 28;4(11):eaau8621. doi: 10.1126/sciadv.aau8621. eCollection 2018 Nov.


Central neurons initiate action potentials (APs) in the axon initial segment (AIS), a compartment characterized by a high concentration of voltage-dependent ion channels and specialized cytoskeletal anchoring proteins arranged in a regular nanoscale pattern. Although the AIS was a key evolutionary innovation in neurons, the functional benefits it confers are not clear. Using a mutation of the AIS cytoskeletal protein βIV-spectrin, we here establish an in vitro model of neurons with a perturbed AIS architecture that retains nanoscale order but loses the ability to maintain a high NaV density. Combining experiments and simulations, we show that a high NaV density in the AIS is not required for axonal AP initiation; it is, however, crucial for a high bandwidth of information encoding and AP timing precision. Our results provide the first experimental demonstration of axonal AP initiation without high axonal channel density and suggest that increasing the bandwidth of the neuronal code and, hence, the computational efficiency of network function, was a major benefit of the evolution of the AIS.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials*
  • Animals
  • Axon Initial Segment / physiology*
  • Cells, Cultured
  • Cytoskeleton / metabolism*
  • Hippocampus / physiology*
  • Mice
  • Nerve Tissue Proteins / metabolism*
  • Neurons / physiology*
  • Potassium Channels / metabolism
  • Sodium Channels / metabolism
  • Spectrin / metabolism*


  • Nerve Tissue Proteins
  • Potassium Channels
  • Sodium Channels
  • betaIV spectrin
  • Spectrin