Not Just a Pack of Neurons

The Neuron Doctrine

Francis Crick famously said ‘you’re nothing but a pack of neurons’ and there are numerous projects underway to recreate a ‘pack of neurons’ (the network of neural interconnections, called the ‘connectome’) in computers. For example:

These are all very worthy projects that should lead be a significant step forward in neuroscience and lead to medical breakthroughs. But they also opens up the prospect of whole brain emulation (see Anders Sandberg’s lecture) with speculation that such emulations would be conscious (see the talk here regarding this).

But below are two recent reminders I stumbled upon that put dents into the doctrine that you just need to consider the neurons…

1. Factor ‘S’

The BBC have recently made the Reith Lectures available online. Colin Blakemore’s ‘Mechanics of the Mind’ lectures of 1976 are still fresh despite the intervening 35 years. In lecture 2, ‘Chang Tzu and the Butterfly’ (available in both PDF
and MP3 forms), he mentions the work of Legendre and Pieron and Pappenheimer.

Around 1907 Rene Legendre and Henri Pieron extracted cerebro-spinal fluid (CSF) from the ventricles within the brains of sleep-deprived dogs (by killing them first). When this CSF was injected into the nervous system of other dogs, the animals fell into a deep sleep. Because of this, they called the fluid ‘hypnotoxin’. Their claims were met with scepticism as efforts to repeat the results failed until Marcel Monnier in the 1960s, working with rabbits. In 1967, John Pappenheimer and others at Harvard Medical School identified an accumulation of an unknown substance dubbed ‘factor S’ as the cause. This was extracted from the cerebrospinal fluid of sleep-deprived goats and then injected into rats and rabbits. In 1982, factor ‘S’ was identified as muramyl peptide. From the work of Jim Kroeger, it is strongly suspected that muramyl peptides originate from the digested remains of bacteria destroyed and excreted by white blood cells. It can be extracted from human urine [New Scientist 7 Jan 1988].

2. Glial Cells

Two recent Scientific American articles examining the role of glial cells –
Andrew Koob’s and Douglas Fields’s. Glia literally means ‘glue’ and until recently was thought only to serve as the glue (maybe ‘frame’ is a better choice of word) to hold the neurons in place. Glial cells outnumber neurons –this is possibly the origin of that urban myth that we only use 10% of our brains. But studies are showing that they perform other roles. One type of glial cell, the astrocyte, has been show to modulate neuron behaviour.

Given just these among many possible examples (the most obvious one being the effect of analgesics, drugs and alcohol and other drugs on the brain), it would be surprising if simulating just the neurons can create a good model of human (or animal) brain behaviour, let alone functionally account for consciousness.

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2 Responses to Not Just a Pack of Neurons

  1. Pingback: Firing and Wiring | Headbirths

  2. Pingback: Backpropagation | Headbirths

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