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. 2015 Nov 10;9:151. doi: 10.3389/fnsys.2015.00151

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Copyright © 2015 Brette.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution and reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Variability due to degeneracy. (A) Spikes can be seen as the result of a sequence of operations applied on an input signal, followed by spike generation. In this view, variability comes from noise added in the spiking process. (B) The state of a physical system can often be described as a minimum of energy. Symmetries in the energy landscape can imply observed variability, whose magnitude bears no relation with the amount of intrinsic noise. (C) An example of the energy view is spike-based sparse coding. A reconstruction of the signal is obtained from combining filtered spike trains together, and spikes are timed so as to make the reconstruction accurate. (D) If the system is redundant, the reconstruction problem is degenerate, leading to several equally accurate spiking solutions (here obtained by permutation of neurons).