Spike Directivity


The  brain activity was continuously recorded  with three extracellular electrodes  close to the active membrane of a single cell.

 
Within this dynamic environment  the occurrences of  action potentials  are perceived as distinct events (see the moment of AP generation, red arrow). Since there is a certain  shape similitude with digital binary on/off phenomena,   the entire phenomenon is  falsely portraying as binary signaling.

This issue regarding the similitude of  shapes didn't help us to understand the huge difference between APs in the brain and simplified digital phenomena. Few have seen real recordings since everywhere highly filtered APs are shown to reinforce the similitude with digital signals. In addition to APs occurrence, recorded signals show a very rich activity  in the vicinity of every neuron which  is not   'noise'. A metaphor may help to perceive this difference. In fact, there is no more similitude between APs and digital signals than it is between jellyfishs and ring parachutes.


The shape in both cases is misleading. Every spike is SPATIALLY MODULATED and this modulation depends on how different axonal branches, dendrites are activated during 1ms  of AP propagation. The action potential generation  is a fast event (1ms) however  it is NOT a DIGITAL signal . This modulation is dependent on how information is processed within a neuron http://neuroelectrodynamics.blogspot.com/p/computing-by-interaction.html
under the influence of many factors (e.g. neurotransmitters, electric fields).  It's not too difficult to demonstrate this mistake since the wave-shapes of extracellular recorded spikes, their width and amplitude are slightly modulated.
However,  before 2005  (Aur et al., 2005) only few have observed that extracellular action potentials are modulated  in a meaningful way (Quirk et al., 2001).  Since AP generation is a fast process many just hypothesized a digital AP and the MISTAKE WAS  LARGELY INCLUDED IN ALL  TEXTBOOKS.

 Since axons express various types of transmitter receptors and different ion channels then the AP is modulated during axonal conduction.Spike directivity (Aur et al., 2005) is a vector  represented in red color that reveals spatial occurrence of electrical patterns during action potential propagation in a neuron (Aur and Jog, 2006).
If electrical patterns predominantly occur in a single axonal branch  then a change  in spike directivity orientation can be computed from recorded action potential shapes

The left turn trial (T-maze task) is represented by yellow and blue arrows while the right turn trial is represented by red and magenta arrows in the same "expert" neuron (Spike directivity vectors  between tone and turn starts in about 20 trials)

In visual object recognition the spike directivity in the same neuron can separate between two different  presented objects (e.g spider and Jennifer Aniston).










(i) About the same firing rate  is recorded in the neuron (8Hz) during both presentations (spider,  Jennifer Aniston)
(ii) Consistently different parts of  recorded  neuron are activated when the spider   or Jennifer Aniston images are presented
The neuron responds to  presented event  and tells that a certain information regarding this event is “read”  or “written”  during the spike.Based on spike directivity data one can predict that Jennifer Aniston was presented  and not the spider. Therefore, the firing rate does not tell WHAT information was “read” or “written”. In fact the firing rate   doesn’t tell the meaning (semantics)
(iii) This is a simple counter example  which shows that information regarding meaning (semantics) is hidden and is not available in the firing rate.
(iv)The counter example strongly refutes the temporal coding hypothesis.
(v) Therefore, any previous experiment  that has proven that firing rate is a good measure to discriminate the meaning (semantics) or claims  the existence of "temporal coding" has to be reanalyzed and reinterpreted. That’s  the idea of counterexample presentation
(vi) To get reliable semantics from experimental data a direct  relationship with "memory" has to be extracted . Spike directivity  provides directly this relationship since it relates specific information  with the  topography of analyzed neuron . See the difference between the spider presentation  and Jennifer Aniston presentation,    specific  parts of the neuron are active. Based on firing rate analysis one cannot distinguish between  the spider and Jennifer Aniston since the firing rate is 8Hz in both cases.
 (vii) Spike directivity reveals what  information is  intracellularly “read” or “written” during the spike and explains the new model of computation by  interaction (NED) that occurs at molecular level in analyzed cell.
The incoming activity from other neurons  has direct effects on intracellular dynamics,  reorganizes internal signaling which can change the propagation of   upcoming  APs . The alteration in spatial  propagation  allows various  intracellular interactions underlying a different information processing inside the cell. The cliché   that individual neurons convey information through firing rate , interspike interval   improperly simplifies the entire process,  disregards  the fact that  always information is  processed within neurons.
From a false hypothesis (stereotype  spike ) following a correct algorithm (statistics) one can demonstrate that Santa Claus is real using firing rate analyzes and electrophysiological recordings. 

This simple observation of spatially modulated APs has powerful, far-reaching impact on
  neuroscience, neurology and provides new directions for neurological disorders treatment
The transition from experimental observation  that contradicts an existent theoretical model to a broad acceptance takes on average 20-30 years  and  requires a change  in a generation of scientists (see Cajal, Belousov-Zhabotinsky, Shechtman). This step is more difficult if the mistake was included in all textbooks
Few have ever recorded or processed action potentials,  many scientists took everything from textbooks or if they perceived the variability of waveforms shapes they have completely ignored it. Unfortunately, the short term desire of any scientist to be part of ‘established science’ is far more important than defending an experimental truth which can change the entire construct.
The attachment to textbook dogma reflects the strong desire of scientists to be part of  'established science' explains this delay (two, three decades) and is independent of recognized credentials.(e.g. Shechtman was not rejected by PhD students).  Cajal  has highlighted a short term consequence:
The good will of scientists is usually so paradoxical that they are more pleased by the defence of an obvious error (DIGITAL APs) which has become wide-spread than by the establishment of a new fact.”
However, always the new generation moves further the entire framework and some of whom cannot adapt themselves to experimental truth remain forgotten scientists  with an obsolete vision.


References:

1. Dorian  Aur, Christopher I. Connolly, and  Mandar S Jog, (2007) Computing spike directivity with tetrodes, Journal of Neuroscience Methods, Volume 149, Issue 1, 30, pp.  57-63; http://dx.doi.org./10.1016/j.jneumeth.2005.05.006 
2. Dorian  Aur, Mandar S. Jog, Building Spike Representation in Tetrodes, Journal of Neuroscience Methods Volume 157, Issue 2 , 30 October 2006, Pages 364-373 , http://dx.doi.org./10.1016/j.jneumeth.2006.05.003
3. Dorian Aur and Mandar Jog - Neuroelectrodynamics- Understanding The Brain Language , IOS Press 2010, http://dx.doi.org/10.3233/978-1-60750-473-3-i
4. Dorian  Aur, Mandar S. Jog, Reading the Neural Code: What do Spikes Mean for Behavior?. Available from Nature Precedings <http://dx.doi.org/10.1038/npre.2007.61.1, 2007
5. Dorian  Aur, Where is the ‘Jennifer Aniston neuron’? , available from Nature Precedings,   http://dx.doi.org/10.1038/npre.2010.5345.2
 6.   Quirk MC, Blum KI, Wilson MA (2001) Experience-dependent changes in extracellular spike amplitude may reflect regulation of dendritic action potential back-propagation in rat hippocampal pyramidal cells. J Neurosci 21:240-248.

1 comment:

  1. When you are listen to a new language for the first time, you may try to catch every single words from the quick stream of a "meaningless" speech.
    We still don't know the language of a single neuron - and also the code of the "choir" of billions of neurons as a brain. The best way to learn a new language is not catching and counting the words but trying to associate single words to objects/stimuli; then few words become a sentence/behaviour and sentences become a full speech/mind.
    Reading and writing information in such a linguistic metaphor could be "speaking" and "talking" between two or even more parts (two or more neurons; even the researcher - who has yet decoded the language of a neuron - and a neuron, ...). After we have learnt the basics of a language we are able to have a proper "conversation", and reading and writing take on a different meaning, in a network of neurons, thus including memory and also what we call consciousness, emotions, even sleep...
    In my opinion NED is a step ahead, please keep going ;) the journey has just begun...

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