Mind Matters News and Analysis on Natural and Artificial Intelligence
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Conceptual illustration of neuron cells with glowing link knots in abstract dark space, high resolution 3D illustration

Even the axons in our nerve cells are “smart PCs”

Your brain is not a computer, it is billions of them

If you want to see your brain in electronic terms, you should picture it as the biggest network imaginable. It’s widely accepted that each neuron in our bodies is complex enough to be something like a little computer. Neurons are considered “pretty weird” on that account:

Unlike their blobby brethren, neurons have distinct regions. There’s the cell body, home to the nucleus. Then come the axons and dendrites, the signal-carrying and signal-receiving parts of the neuron that send long, spindly arms to form connections, called synapses, with other neurons.

Harvard Medical School, “Once seen as nerve cells’ foot soldier, the axon emerges as decision-maker” at ScienceDaily

But the system turns out to be “far more complex than once thought” because, contrary to expectations, far-flung regions (thousands of cell body widths from their nucleus) can even make independent decisions:

“We are not the first to think that there has to be some autonomy,” said Jeffrey Macklis, a neuroscientist at Harvard Medical School and the Max and Anne Wien Professor of Stem Cell and Regenerative Biology at Harvard University. “It would take several hours for a growth cone to signal back to its nucleus for a ‘next command,’ and it has been clear from observing axon growth in the lab that growth cones can move toward targets even if severed from their cell bodies.” 

Harvard Medical School, “Once seen as nerve cells’ foot soldier, the axon emerges as decision-maker” at ScienceDaily

In mouse studies, they found that the outermost tips of the axons (“growth cones”), featured “much of the molecular machinery of an independent cell, including proteins involved in growth, metabolism, signaling and more.” In short, the nucleus is not necessarily the control center of a neuron. Intricate decision-making includes semi-independent constituents of the cell, far from the central command. As Dr. Macklin says, “It’s a whole new way of thinking about neurons.”

We often compare living systems and computers but the comparison with the brain certainly needs updating:

The cell body of a neuron has been traditionally thought of as a mainframe computer with axons like copper wires being directed to its synapses. But this new work suggests another model. Macklis proposes that the cell body may be like a server connected to smart PCs that have the capability to interface with the world…

“What our findings demonstrate is that a neuron, unlike a kidney or liver cell or most cells we think about, doesn’t have a single transcriptome or proteome, but, rather, it has multiple, subcellularly localized transcriptomes and proteomes,” Macklis said.

Harvard Medical School, “Once seen as nerve cells’ foot soldier, the axon emerges as decision-maker” at ScienceDaily Paper. (paywall)

This finding about axons (the signal-carrying parts of the neuron) complements one about dendrites (the signal-receiving part), likewise from mouse studies, in 2013. Dendrites were conventionally thought to merely receive signals passively.

When you look at the hands of a clock or the streets on a map, your brain is effortlessly performing computations that tell you about the orientation of these objects. New research by UCL scientists has shown that these computations can be carried out by the microscopic branches of neurons known as dendrites, which are the receiving elements of neurons… The results challenge the widely held view that this kind of computation is achieved only by large numbers of neurons working together, and demonstrate how the basic components of the brain are exceptionally powerful computing devices in their own right.

Senior author Professor Michael Hausser commented: “This work shows that dendrites, long thought to simply ‘funnel’ incoming signals towards the soma, instead play a key role in sorting and interpreting the enormous barrage of inputs received by the neuron. Dendrites thus act as miniature computing devices for detecting and amplifying specific types of input.

University College London, “Smart neurons: Single neuronal dendrites can perform computations” at ScienceDaily  Paper.(paywall)

One science writer summarized the situation:

The brain is not a supercomputer in which the neurons are transistors; rather it is as if each individual neuron is itself a computer, and the brain a vast community of microscopic computers. But even this model is probably too simplistic since the neuron processes data flexibly and on disparate levels, and is therefore far superior to any digital system. If I am right, the human brain may be a trillion times more capable than we imagine, and “artificial intelligence” a grandiose misnomer.

Brian J. Ford, “The secret power of the single cell” at New Scientist (2010)

We should keep this in mind when we hear amazing claims for the power of artificial intelligence.

See also: The brain exceeds the most powerful computers in efficiency. Eric Holloway: Human thinking takes vastly less computational effort to arrive at the same conclusions

The brain is not a meat computer

and

Yes, your brain is a machine—if you choose to see it that way (Michael Egnor)

Hat tip: Philip Cunningham


Even the axons in our nerve cells are “smart PCs”