Updating Cajal

The Neuron Doctrine, Redux presents the multitude of interactions among neurons and non-neuronal central nervous system cells that were not included in Cajal's original formulation.

Camillo Golgi developed the silver staining technique that allowed Santiago Ramon y Cajal (picture at right) to visualize individual neurons. His cell images allowed him to successfully argue that neurons were not intimately connected, but rather they communicated via synapses. They shared the Nobel Prize in 1906.

Techniques have improved and new ones have evolved since Golgi and Cajal were experimenting. There are (1) gated gap junctions between neurons that allow some degree of electrical transmission, (2) receptors to neuromodulatory substances outside of the synapse, (3) the presence of axon-glial communication, (4) interactions between glial cells via neurotransmitters and electrical transmission.

With 100 billion nerve cells talking, and then the multiple ways they can, the possibilities are limitless.

Ramachandran: "The number of possible permutations and combinations of brain activity, in other words the numbers of brain states, exceeds the number of elementary particles in the known universe." Bullock et al: "This suggests that the complexity of the human brain and likely other regions of the nervous system derive from some organizational features that make use of the permutations of scores of integrative variables and thousands or millions of connectivity variables."

There is, however, a higher organization of action potentials, as seen on electroencephalograms. "The permutation and combinations of brain activity" are limited by the very organizations and connections that suggest their infinite arrangements. EEG may one day emerge as an old tool answering new questions.

Bullock, T.H., Bennett, M.V.L., Johnston, D., Josephson, R., Marder, E., Fields R.D. 2005. The Neuron Doctrine, Redux, Science, V.310, p. 791-793
Ramachandran VS. A Brief Tour of Human Consciousness: From Impostor Poodles to Purple Numbers. Pi Press, New York, 2004.