Memristor-Using Circuit with Neuron-like Behavior

The memristor is a type of electrical circuit that can change its resistance level to electrical conduction based on the amount of current flowing through it and remember the last resistance level it was at when current is stopped, hence the name. Pretty nifty.

These have been known about in theory since 1971, but haven't found any truly practical application until research published on 19 December 2009 in the Proceedings of the National Academy of Sciences from Hewlett-Packard's laboratories in Palo Alto, California led to a dynamic, self-reprogramming Boolean (named after computer scientist George Boole) sum-of-product circuit.

Published 16 December 2012 in the journal Nature, researchers R. Stanley Williams -- who was on the team that published the 2009 memristor article -- Matthew D. Pickett, and Gilberto Medeiros-Ribeiro have shown that memristors can be used with what are called Mott insulators to build and release a charge using heat. They do this by using material that is not very electrically conductive at lower temperatures due to interactions among the electrons that prevent them from conducting, or flowing out in the same direction. At higher temperatures, as the current increases, these interactions decrease, the electrons begin to agree, and the memristor turns into a conductor, allowing a charge to be released.

Using these "Mott memristors", the team has created what they dub the neuristor using the material niobium dioxide. A bit of background on neurons, the analogous biological brain cells that the team is attempting to emulate: Unlike binary computer systems that communicate information via states that are simply either on or off (1 or 0; high voltage/low voltage), neurons communicate information by spiking from less excited states with electrical activity to various degrees on gradients, and networking with other neurons that are spiking at the same frequencies to produce spiking patterns that represent perceptions.

The neuristor is a memristor-capacitor circuit that is capable of networking capacitor-checked memristors so that their outputs spike at certain frequencies, much like neurons. They are much more regular than neuronal spiking, but as John Timmer writes for Ars Technica, "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."

Continues Timmer:

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."

As it currently stands, the NbO₂ neuristor uses too much power to put in large numbers on a chip. But there are other types of Mott resistors known, and the authors think that it should be possible to find one that's both low power and compatible with current chip-making techniques.

Quantum computing still has quite a way to go, and artificial intelligence as we oft dream of it would probably rely on the kinds of raw computing power quantum computing can offer, but these new neuristors appear promising for modeling neuronal behavior in silicon circuitry.