Tuesday, 12 July 2011

The Myth of Temporal Coding

Starting with Adrian's recordings the idea was that the neural code was embedded in  temporal patterns. Therefore,  in the last sixty years everything was felt to revolve around temporal patterns.
However, the main hypothesis of computational  neuroscience ( digital-like uniformity of action potentials) is not validated by recent experimental data [1],[2].
 From a false hypothesis (stereotypical spike) one can reach  false conclusions following  a correct analysis of data. The unrealistic hypothesis  impacted model validity, created a strong debate and generated unrealistic predictions  in behavioral studies, visual object recognition (e.g. grandmother cell).


The power of  counterexamples

We completely understand the frustration of neuroscientists regarding temporal coding. For more than 60 years they have tried to prove that temporal coding is the right model of  information processing that reflects the subtle nature of neural code. The paradox is that the same experiment used to show the organization of temporal patterns proves the fallacy of temporal coding. The procedural T-maze learning task became the best counterexample for temporal coding theory http://neuroelectrodynamics.blogspot.com/p/spike-directivity.html. Currently, we can provide other  examples, however there is no need to generate new evidence. That’s the beauty of counterexamples and experimental design. You only need one single counterexample to throw down a "solid"theoretical construct. Quoting Feynman "It doesn't matter how beautiful your theory is, it doesn't matter how smart you are or how many years you can keep a theory alive ! If it doesn't agree with experiment, it's wrong."
With a  digital (stereotype) spike, the temporal coding theory was born dead.

All issues in interpretation are generated by this  FALSE hypothesis of 
a  digital (stereotype) spike, see the analogy:
a. 3=-3                   -------                    (3)2=(-3)2              -----                        9=9
b. (FALSE hypothesis) ------     (operation/transformation) ---- (CORRECT/ FALSE ?)
A.Stereotype spike    --------  adding spikes/firing rate   -------CONTROVERSIES
B. (FALSE hypothesis) ------- (transformation, STATISTICS )  -- CORRECT /FALSE ?



Therefore,  Bayes theory, nonlinear dynamics  ... have no real value if they are attached to a false hypothesis (digital spike). One can learn mathematics, solve complex problems without pretending to apply the mathematical theory to understand  ‘neural code’.  In fact  many controversies in the field were generated by keeping alive the reductionist  temporal coding paradigm, they lead to  inconsistent and naive interpretations regarding place cells, concept cells or mirror neurons.

References

1. Dorian Aur , Christopher I.  Connolly, Mandar S. Jog, 2005, Computing spike directivity with tetrodes, Journal of Neuroscience Methods, 149 (1), pp. 57-63.
2. Takuya Sasaki, Norio Matsuki, Yuji Ikegaya, 2011, Action-potential modulation during axonal conduction Science 331 (6017), pp. 599-601