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.
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
many fields, in computer science http://neuroelectrodynamics.blogspot.com/p/computing-by-interaction.html
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.
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.
ReplyDeleteWe 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...