'Neuristor' Acts Like Your Brain's Neurons
The computer you're using now to read this article makes use of binary switches which (as the name suggests) have only two states, on or off. The individual neurons of your brain, on the other hand, perform their function using a different model of activity. Neurons exhibit spikes of activity; information can be encoded in the pattern of spiking. HP researchers have created a hardware device comprised of "neuristors" that mimic this behavior:
The people at HP labs who have been working on memristors have figured out a combination of memristors and capacitors that can create a spiking output pattern. Although these spikes appear to be more regular than the ones produced by actual neurons, it might be possible to create versions that are a bit more variable than this one. And, more significantly, it should be possible to fabricate them in large numbers, possibly right on a silicon chip.
The key to making the devices is something called a Mott insulator. These are materials that would normally be able to conduct electricity, but are unable to because of interactions among their electrons. Critically, these interactions weaken with elevated temperatures. So, by heating a Mott insulator, it's possible to turn it into a conductor. In the case of the material used here, NbO2, the heat is supplied by resistance itself. By applying a voltage to the NbO2 in the device, it becomes a resistor, heats up, and, when it reaches a critical temperature, turns into a conductor, allowing current to flow through. But, given the chance to cool off, the device will return to its resistive state. Formally, this behavior is described as a memristor.
To get the sort of spiking behavior seen in a neuron, the authors turned to a simplified model of neurons based on the proteins that allow them to transmit electrical signals. When a neuron fires, sodium channels open, allowing ions to rush into a nerve cell, and changing the relative charges inside and outside its membrane. In response to these changes, potassium channels then open, allowing different ions out, and restoring the charge balance. That shuts the whole thing down, and allows various pumps to start restoring the initial ion balance.
In the authors' circuit, there were two units, one representing the sodium channels, the other the potassium channels. Each unit consisted of a capacitor (to allow it to build up charge) in parallel to a memristor (which allowed the charge to be released suddenly. In the proper arrangement, the combination produces spikes of activity as soon as a given voltage threshold is exceeded. The authors have termed this device a "neuristor."
"Neuristor" is a term coined by visionary computer science engineer Hewitt Crane in his PhD thesis in 1958. However, sf writers have made good use of the word. Robert Heinlein constructed the artificially intelligent computer Mycroft Holmes in his 1966 novel The Moon is a Harsh Mistress out of neuristors. Roger Zelazny used the idea of a neuristor brain to great effect in his 1976 novella Home is the Hangman.
The earliest reference that I know about is the artificial, inorganic artificial brain from Edmond Hamilton's 1926 story The Metal Giants:
No doubt it was a startling proposition, to construct an artificial brain that would possess consciousness, memory, reasoning power...
...Detmold had attacked the problem from a different standpoint. It was his theory that the sensations of the nervous system are flashed to the brain as electric currents, or vibrations, and that it was the action of these vibratory currents on the brain-stuff that caused consciousness and thought. Thus, instead of trying to make simple, living cells and from them work up the complicated structure of the brain, he had constructed an organ, a brain, of metal, entirely inorganic and lifeless, yet whose atomic structure he claimed was analogous to the atomic structure of a living brain. He had then applied countless different electrical vibrations to this metallic brain-stuff, and finally announced that under vibrations of certain frequencies the organ had showed faint signs of consciousness.
Via Arstechnica; see also A scalable neuristor built with Mott memristors.
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