Spikelets in Pyramidal Neurons: Action Potentials Initiated in the Axon Initial Segment That Do Not Activate the Soma

PLoS Comput Biol. 2017 Jan 9;13(1):e1005237. doi: 10.1371/journal.pcbi.1005237. eCollection 2017 Jan.


Spikelets are small spike-like depolarizations that can be measured in somatic intracellular recordings. Their origin in pyramidal neurons remains controversial. To explain spikelet generation, we propose a novel single-cell mechanism: somato-dendritic input generates action potentials at the axon initial segment that may fail to activate the soma and manifest as somatic spikelets. Using mathematical analysis and numerical simulations of compartmental neuron models, we identified four key factors controlling spikelet generation: (1) difference in firing threshold, (2) impedance mismatch, and (3) electrotonic separation between the soma and the axon initial segment, as well as (4) input amplitude. Because spikelets involve forward propagation of action potentials along the axon while they avoid full depolarization of the somato-dendritic compartments, we conjecture that this mode of operation saves energy and regulates dendritic plasticity while still allowing for a read-out of results of neuronal computations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / physiology*
  • Axons / physiology*
  • Computational Biology
  • Computer Simulation
  • Models, Neurological*
  • Pyramidal Cells / physiology*

Grants and funding

This work was supported by the Deutsche Forschungsgemeinschaft (www.dfg.de; Research Training Group “Sensory Computation in Neural Systems”; grant number GRK 1589/2); the Bundesministerium für Bildung und Forschung (www.bmbf.de; Bernstein Center for Computational Neuroscience Berlin, grant number 01GQ1001A to RK; Bernstein Focus “Neuronal Basis of Learning”, grant number 01GQ0972 to RK; and grant number 01GQ0901); and the Einstein Stiftung Berlin (www.einsteinfoundation.de; Einstein International Postdoctoral Fellow: MWHR). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.