The Brains Electromagnetic Field

At rest, the neuronal membrane forms a dipole in which the inside of the membrane is negatively (about -65 mV) charged in relation to the outside of the membrane. This charge difference is maintained by the action of ion pumps that pump cations (principally sodium and calcium) out of the neuron. Brain neurons are densely packed, with about 104 neurons/mm2 so the fields of adjacent neurons will not be discrete but form a complex overlapping field made up of the superposition of the fields of millions of neurons in the vicinity. The electrical field at any point in the brain will be a superposition of the induced fields from all of the neurons in the vicinity and will depend on the geometry and the dielectric properties of neurons and tissue. The combined activity of all the neurons in the brain generates a complex electromagnetic field whose strength can be estimated from theoretical principles and measured during EEG or MEG, and is about 20-250 V/m [34].

When any neuron receives a signal from upstream neurons, synaptic transmitters stimulate ion pumps that cause the membrane to become more or less negatively polarized, depending on the type of signal received. If the membrane charge falls below about -40 mV then the neuron "fires" and a chain of depolarizations is triggered that travels along the neuron and stimulates release of neurotransmitters. Conventional neurobiology has focused on the chemical signal that is transmitted from one neuron to another. There is absolutely no doubt at all that most of the information processing performed by the brain is due to this type of signaling. However, the massive membrane depolarization will also generate an electromagnetic field perturbation that, traveling at the speed of light, will influence the probability of firing of adjacent neurons. Vigmond [44] modeled the electrical activity of pyramidal cells and demonstrated that neuron firing induced a peak of intracellular potential in receiver cells that ranged from a few microvolts to 0.8 mV, decaying with approximately the inverse of distance between the cells. For neurons that are arranged randomly, their induced fields will tend to sum to zero; but the laminar organization of structures such as the neocortex and hippocampus, with parallel arrays of neurons, will tend to amplify local fields. Using the model, a peak intracellular voltage of 2600 V/m (and thereby above the thermal noise level in the membrane) will be induced in receiving cells if they are located within a radius of 73-77 |m from the source cell [34]. Considering only those cells in the plane of the source cell embedded in the human cerebral cortex (about 104 neurons/mm2), then approximately 200 neighboring cells will be within that field volume. The firing of a single neuron will thereby be capable of modulating the firing pattern of many neighboring neurons through field effects.

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