Humans are different

Humans are different

The popular article in Medicalxpress (see this) tells about highly interesting observation described in the Nature article “Allometric rules for mammalian cortical layer 5 neuron biophysics” by Mark Harnett (see this).

The finding is that the density of voltage gated channels in the human brain is dramatically lower than in other mammalian brains.

1. The neuronal system studied was layer 5 pyramidal neurons. Dendrites of these neurons were considered. Densities of voltage gated channels per neuron volume and per brain volume were studied. The ion channels studied were Na and K channels. The channels considered are ion pumps and need metabolic energy.

10 mammalian species were studied so that cortical thickness and neuron size were the varying parameters. As the neuron size increases, the density of neurons decreases.

Humans were found to be an exception. The density of the channels per brain volume is dramatically reduced. The proposed interpretation is that this reduces the amount of metabolic energy needed to generate action potentials and the metabolic energy is used for other purposes. Before continuing, it is good to recall some basic facts about neurons. Synapses, dendrites, and myelination are the basic notions needed if one tries to understand these findings. It is enough to notice that most synaptic contacts are between axons to dendrites but that almost any other combinations are possible. Myelination is mostly for axons and only rarely for dendrites. The dendrites of the excitatory pyramidal cells studied in the article are profusely decorated with dendritic spines.

Could the TGD view about the brain allow us to interpret these findings? Why would the density of the voltage gated ionic channels be smaller for pyramidal dendrites? How could this relate the evolutionary leap leading to the emergence of humans?

1. In the TGD framework, nerve pulses do not mediate information between neurons but make possible transfer of information between them using dark photon signals.

Nerve pulse patterns however generate dark Josephson radiation transferred to the magnetic body (MB) of the brain. Dark Josephson radiation is characterized by length and time scales proportional the value of h_eff, which is quite large implying that the wavelengths λ= ch_eff/E of dark photons with energy of visible photon can be of order Earth size.

This gives rise to a temporal variation transformed to a sequence of pulses if the receiving end at MB has cyclotron resonance frequency at the average value of Josephson frequency. The outcome at MB is analogous to a nerve pulse pattern.

Second function could be to act as a relay connecting the flux tubes of presynaptic neuron and postsynaptic neuron to a single flux tube acting as a longer waveguide. Keeping the communication lines open only when they are used could save energy as it does in human communications.

Only vertebrates have myelinated axons, which suggest that their emergence was a cognitive leap involving emergence of layers of MB with larger h_eff and larger scale. The emergence of EEG mediating information to layers of MB with size scale of Earth for 10 Hz alpha band would relate to this leap.

Also dendrites can be myelinated but the fraction of myelinated dendrites is small. For instance, myelinated dendrites can appear in the olfactory system. Therefore the idea that myelination of dendrites in the human brain could explain the finding does not look plausible.

Why would the dendrites of the olfactory system be myelinated? Myelination would reduce dramatically the spatial resolution of the olfactory percept at MB. Olfactory sense is indeed very rough and one cannot speak about spatial distribution of a smell. Does this mean that the world of smells is much richer for invertebrates? What could the reduction of the density of voltage gated channels mean? Why would the distances between voltage gated channels be longer for humans and what does this imply?

1. The TGD inspired proposal is that humans differ from other mammals in that the value of h_eff involved is considerably larger for some neurons. In fact, the TGD inspired model for the generation of language assumes that the value of h_eff for MBs of language genes is considerably larger than for other genes.
2. The average distance between voltage gated ionic pumps defines a spatial resolution scale and is a good candidate for the minimum wavelength λ assignable to a signal propagating along the dendrite. For an ordinary photon, λ defines energy, which must be above the thermal energy at physiological temperatures. This minimum energy is rather near to the minimal energy of the ordinary Josephson photons associated with membrane potential (about .05 eV) and the corresponding wavelength is 14.8 μm.

Also other kinds of signala can propagate along the axon. The inspired model for nerve pulse proposes that nerve pulses could correspond to perturbations of oscillating Josephson current which in the rest state corresponds to a propagating sequence of Sine-Gordon solitons mathematically analogous to a sequence of rotating gravitational penduli. Nerve pulse corresponds to a perturbation, which kicks some pendul from rotational to an oscillating motion and this perturbation propagates along the axon with the same velocity as nerve pulse.

The natural guess is that the resolution scale is proportional to ℏ_eff,B at intra-brain flux tubes in turn proportional to ℏ_eff,MB for the flux tubes at the MB of brain having quantal length scales much longer than brain size. The range of variation of the spatial resolution could correspond to the variation of ordinary photon wavelengths between visible wavelengths (of order μm) and IR wavelengths of order 14.8 μm. Note however that the lengths of myelinated portions are about 100 μm.

For a summary of earlier postings see Latest progress in TGD.

Articles and other material related to TGD.