What are neural spikes?

Rate-coding

Interval-coding

Facts about spikes3


Since the brain consumes a disproportionate fraction of the body’s energy (around 20%), and the majority of that energy is used to fuel neural spikes, it seems unlikely that the energy advantage of interval-coding would be ignored by evolution. The max-entropy interval distribution provides clear evidence for information-theoretic optimization, in my opinion, so I think it’s safe to conclude interval-coding would be preferred wherever information processing is occuring. That said, it’s thought that neurons in some species use analog coding methods,4 and rate-coding is known to be used for muscle actuation, so interval-coding is likely not the whole story. Furthermore, as Shannon realized, knowing the encoding method doesn’t tell us anything about the signal content.

We haven’t yet considered how information is grouped. Are there packets, as in networking protocols like TCP? Or is the information a continuous stream? Personally, I think packets are much more likely, since neurons need a way to distinguish a lack of activity from an unusually long inter-spike interval. Packets also permit simple error detection, with parity bits and checksums. I haven’t yet found good evidence for either position, so this is a direction for future research.


  1. Enoka RM, Duchateau J. Rate Coding and the Control of Muscle Force. Cold Spring Harb Perspect Med. 2017;7(10):a029702. Published 2017 Oct 3. doi:10.1101/cshperspect.a029702 ↩︎

  2. Brette R. Philosophy of the Spike: Rate-Based vs. Spike-Based Theories of the Brain. Front Syst Neurosci. 2015;9:151. Published 2015 Nov 10. doi:10.3389/fnsys.2015.00151 ↩︎

  3. Cessac, B., Paugam-Moisy, H., & Viéville, T. (2010). Overview of facts and issues about neural coding by spikes. Journal of physiology, Paris, 104(1-2), 5–18. https://doi.org/10.1016/j.jphysparis.2009.11.002 ↩︎

  4. Li, Z., Liu, J., Zheng, M., & Xu, X. Z. (2014). Encoding of both analog- and digital-like behavioral outputs by one C. elegans interneuron. Cell, 159(4), 751–765. https://doi.org/10.1016/j.cell.2014.09.056 ↩︎