Hi Russel & Gang,

I just sent this around to an internal email group ....
=======================================
Hi,
It occurred to me that the latest empirical evidence surrounding brain endogenous fields (the subject of my PhD thesis) may be of general interest to the group. The actual science (and supplementary material) is here:


*Anastassiou, C. A., Perin, R., Markram, H. and Koch, C. 'Ephaptic Coupling of Cortical Neurons'
Nature Neuroscience vol. 14, no. 2, 2011. 217-223.
*
The result has also been summarized at physorg here

"Neurobiologists find that weak electrical fields in the brain help neurons fire together" http://www.physorg.com/news/2011-02-neurobiologists-weak-electrical-fields-brain.html

I'd like to encourage everyone to consider that the role of fields is likely to impact neural modelling in due course. The little capacitor in the Hodgkin Huxley model is going to get a lot of attention!

Meanwhile, the context of my PhD is one of supplying the mechanism. The empirical work reveals the phenomenon. The researchers involved have no mechanism. It is, formally, a mystery. In my PhD I have described the most plausible mechanism - ion-channel fields - for the action potential component only. I am setting out at the moment to add the chemical synapse component and electrical synapse (gap-junction) components. Hopefully I'll get a chance to actually demonstrate how the fields involve themselves in the variability in firing synchrony (as a separate feedback mechanism).

If you want to be able to communicate the effect, the buzzword (which I don't like!) is 'ephaptic coupling'. It is also interesting to note that the scientist behind the 'Blue Brain' project (Markram) has teamed up with one of the worlds heavy hitters in the realm of the neurobiology of consciousness (Koch).

cheers
colin hales
===========================================

In my PhD I it took >150,000 hours of supercomputing to show that the EM fields have a whole degree of freedom not in existing neural modelling. The exact same action potential firing can result in an infinity of different local field potentials and these are not merely the result of chemical synapses. Action potentials and electrical synapses contribute their component. I have provided the ultimate mechanism for the fields (electric AND magnetic).

The empirical work mentioned above is the 'icing on the cake'. It shows empirically that the fields themselves self-impact the neural processes and alter the firing dynamics in radical ways at microscopic levels within the tissue. The days of the fields as epiphenomena are over. The view my work supports is one where the EM fields and the action potentials act in a sort of longitudinal/transverse quadrature resonance, two axes mutually altering each other. The mutual interaction does not require large fields ...1v/m will do at the membrane level. These fields have a radical effect on action potential _phase_ and thereby impact whole-tissue field coherence from the single neuron level up. If you plot the field due to a single neuron action potential it beams and dwells and rotates like an active phased array antenna. Baths itself and its neighbours within 1mm with a highly controlled, directed beam effect.

"Ephaptic coupling" is the effect...for some reason biosciences think their EM is different! :-) We all know it as simple EM coupling.
Pretty cool huh? Change is afoot.

cheers
colin



Russell Standish wrote:
Neurobiologists Find that Weak Electrical Fields in the Brain Help
Neurons Fire Together

http://media.caltech.edu/press_releases/13401

Reminds me of what Colin says he is doing...

Cheers


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