In the geon model, the mind is a geon composed of gravitational waves (gravitons) which are produced by synchronous firing of neurons during a theta cycle. Information in the mind is encoded in the patterns of gravitational waves within the geon. For the brain to interact with the mind, neurons must be able to absorb a significant amount of energy from the geon, resulting in the generation of action potentials such as the firing of grid cells when they reach their firing fields (see previous chapter). The big question is: how can neurons absorb gravitons? It is easy for a system to absorb photons, but to absorb gravitons is not a simple matter.

Absorption of Gravitons by Molecules

We know that a molecule can absorb a photon by "resonance", that is, if the molecule has two states with energy difference the same as the photon. Theoretically, a molecule can also absorb a graviton by resonance, but the probability is very small. This is because the gravitational interaction is extremely weak, compared to the electromagnetic interaction.

No one knows the exact relative strength between gravitational interaction and electromagnetic interaction. Based on the Newton's law for gravity and the Coulomb's law for electricity, the gravity/electricity ratio is only 10^-42 if we use two electrons for comparison. However, this ratio becomes 10^-36 if two protons are used. It is unclear which one is correct, perhaps both are not accurate. The real answer may require quantum gravity which has not been well developed.

As estimated in Chapter 7, a conscious geon may consist of 10²² gravitons. The lifetime of a conscious geon is about 0.2 second, which is much longer than the time needed for a molecule to absorb a photon (typically less than 10^-12 second). Therefore, the huge number of gravitons and the long interaction time have dramatically increased the probability for a neuron to absorb gravitons. Further enhancement of the probability can be achieved by using a large number of "gravitoreceptors" that have resonant frequencies with gravitons. The gravitoreceptors could be microtubules which are a major component of cytoskeleton.

Microtubules and Fröhlich Condensation

A neuron contains a sea of microtubules which may absorb gravitons if they have the right resonant frequencies. Vibrational frequencies around 10 MHz have indeed been observed in microtubules (reference). Therefore, the total amount of energy absorbed by microtubules in the long axon and in hundreds or even thousands of dendrites should be quite significant. However, most microtubules are not directly participating in the generation of action potentials, which are initiated at the axon initial segment (AIS) (reference). It is likely only the microtubules in AIS are directly involved in neuronal firing. The energy absorbed by microtubules at other regions would be wasted if it cannot propagate to AIS. Usually, a physical system tends to reach thermal equilibrium and every microtubule would get some energy from the geon. In this case, the microtubules in AIS could get only a small fraction of total energy.

In 1968, Herbert Fröhlich discovered a process that is exactly what we need. This process is known as Fröhlich condensation. It has been shown theoretically that if sufficient energy is supplied to a system of coupled oscillators, most of the supplied energy can concentrate around the lowest vibrational mode. The Fröhlich condensation has not been observed yet, but computer simulations have indicated that the 10 MHz vibration in microtubules is a possible candidate (reference).

With the help of Fröhlich condensation, the total absorbed energy from the long axon and dendrites can be channeled to the microtubules with lower vibrational frequencies. These particular microtubules could be located in AIS to regulate neuronal excitability.

AIS is a specialized portion of the axon, located between the axon hillock (where the axon starts) and the beginning of the myelin sheath. It contains high density of voltage-gated sodium and potassium channels. During information transmission, dendrites receive inputs from other neurons, resulting in graded membrane potential changes which converge at the AIS. If the membrane potential at AIS exceeds a threshold, the action potential will be generated. The particular microtubules may regulate neuronal firing at this strategic location.

The organization of microtubules in AIS is entirely different from other regions. Under electron microscope, it can be seen that they assemble into bundles called fascicles. In the pyramidal neuron of the rat cerebral cortex, most fascicles contain 6 to 12 microtubules, but some fascicles contain only 3 or 4. Single microtubules are also present, but less visible under the microscope. The sizes of both the individual and fasciculated microtubules appear to be the same. The total number of microtubules in AIS varies between 22 and 50. They run parallel to the long axis of the axon. Some of them are near the plasma membrane (reference).

The microtubules in AIS, either single or in fascicles, will be called "gating microtubules" because they may work with Tau proteins to regulate neuronal firing.

The Role of Tau Proteins

Tau is one of several types of microtubule-associated proteins (MAPs) which regulate the assembly and stability of microtubule networks. Although microtubule networks exist in all kinds of animal and plant cells, Tau is present only in neurons and predominantly localized in axons. This unique feature suggests that Tau may have neuron-specific functions. The following figure illustrates a possible function which can also explain the pathogenesis of Alzheimer's disease (more info).

Experiments have demonstrated that Tau proteins can associate with the plasma membrane (reference). These membrane-associated Tau proteins may also bind with gating microtubules, either single or in fascicles. A microtubule molecule is highly negatively charged, about 50 electron charges per tubulin dimer (the building block of microtubules) (reference). Upon binding to Tau proteins, gating microtubules can exert a hyperpolarizing field on voltage-gated sodium and potassium channels, reducing their opening probability. Thus, binding between gating microtubules and membrane-associated Tau proteins has inhibitory effect on neuronal firing. The energy received from the geon can induce vibration of the gating microtubule. This vibration may shake off the microtubule from Tau proteins, thereby increasing neuronal excitability.

This simple mechanism can be used to decode the gravitational wave patterns in the geon, as discussed in the next chapter.

Last updated: February 20, 2011

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