Tag Archives: Dendritic calcium levels

How the brain really works (maybe) – 2

I sent the previous post to a very intelligent friend — a PhD Electrical Engineer who responded as follows

“Correct me if I’m wrong, but it sounds like you are proposing that in addition to direct communication in the nervous system via electrical and chemical synapses, you are proposing that there could also be communication coupling in nerve fibers via local electric fields. But isn’t this a known phenomenon, ephaptic coupling? See
https://en.wikipedia.org/wiki/Ephaptic_coupling”

I didn’t think EE’s knew about such things (but I told you he’s very smart). Here are a few extra points of mine concerning his response and the article in general.

Excellent point. Thanks. What I propose could certainly be called ephaptic transmission. It has been well described between two axons in peripheral nerves (this was the initial description). Ephaptic transmission is fairly well established in muscle (which also has action potentials spreading along the muscle fiber allowing it to contract). Investigation in the brain has primarily been between adjacent neurons or adjacent axons. Questions have arisen as to whether it could be a mechanism of seizure generation.

As far as I can tell, the following ideas are actually original.
(1) Ephaptic transmission could normally occur between dendrites in the cerebral cortex.
(2) The brain and cerebral cortex is built the way it is to allow dendritic ephaptic transmission to occur.
(3) This is the way serious computations are carried out by the cerebral cortex.

Why now? Probably because there was no way of measuring dendritic electric potential changes directly before this paper (prior to this calcium levels in dendrites were used as a surrogate). Another example of new technology driving the science.

I didn’t put it in the original post, but actual paper notes that the potential flucutations across the dendritic membrane were much larger than the fluctuations recorded at the cell body.

People have wondered for years how various electrical activities in the brain could be synchronized over large areas (every electrical wave seen in the electroencephalogram is the activity of hundreds of thousands to millions of neurons). This may be an explanation — previously people had figured that it was coming from neurons lower in the brain (particularly the thalamus) sending axons all over the place stimulating neurons simultaneously. Even this doesn’t really work, because various areas of the brain are separted from each other, axonal speed is thought to be constant, and the impulses have different distances to travel.

One disturbing aspect to the picture in the previous post — If you regard that neuron as embedded in a cube 50 x 50 x 50 microns on a side, you’d get about 8,000 neurons per cubic millimeter (1,000 x 1,000 x 1,000 cubic microns). The literature says over twice that at 20,000 neurons/cubic millimeter.

I doubt that the above constitutes all the implications of these ideas. Any comments? I am quite interested to hear them.