03 April 2010

Memristor Update and Video

The discovery of the memristor derives from the search for a rigorous mathematical foundation for electronics by a young electronics engineer at the University of California, Berkeley, Leon O. Chua. Chua’s analysis suggested there was a fourth foundational circuit element missing from the standard trio of resistor, capacitor and inductor. He called it “memristor.” In 1971, he published a seminal paper on this missing basic circuit element.

...Jumping forward to 2010, the work of Dr. Wei Lu’s University of Michigan team now confirms that memristor circuits indeed behave like synapses. Lu’s team used a mixture of silicon and silver to join two metal electrodes, mimicking how synapses allow neurons to learn new firing patterns — not unlike a slime mold’s ability to anticipate events. The timing of electrical signals in two neurons anticipates how later messages can jump across the synapse between them. When a pair fires, the given synapse becomes more likely to pass later messages between the two. “Cells that fire together, wire together,” says Lu.

Just like a synapse, the memristor changes its resistance in varying levels. Dr. Lu found that memristors can simulate synapses because electrical synaptic connections between two neurons can seemingly strengthen or weaken depending on when the neurons fire. “The memristor mimics synaptic action,” Lu concludes. Dr. Nadine Gergel-Hackett at NIST acknowledges the Michigan team’s successful creation of a brain synapse analog. “This work is a large step towards the realization of biology-inspired computing,” she says. _hplus

This electronic approach to an artificial synapse may help in the quest to build a bottom-up artificial brain. The neo-cortex contains about 10 billion neurons, with each neuron making approximately 10,000 connections (or more). The synaptic approach to cognition is only one of several approaches that neuroscientists and cognitive scientists have taken. But it is a fairly good place to start.

Neurons are also connected to each other via "gap junctions" -- direct ion exchange pathways between neurons. Other cells are also involved intimately with neuronal function -- the glial cells. No one actually understands how the brain generates cognitive activity, or consciousness.

But if scientists can create realistic artificial brains that can be tested and monitored in exquisite detail at every stage of input, output, and anything in between, it is quite likely that we will learn something.

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