29 January 2010

Nanotech Builds a Synaptic Beginning

French researchers have built an artificial synapse using a combination of gold nanoparticles and an "organic transistor." The tiny device was designed to mimic the short term learning behaviour of a single synapse. Understand that it is a bare beginning -- since neurons have thousands of synapses, and there are tens of billions of neurons in the neocortex.
The team, which includes scientists from the CNRS (the French National Science Agency) and CEA (the French Atomic Energy Commission), began by adding gold nanoparticles to the interface between an insulating layer (gate dielectric) and an organic transistor made of pentacene. They fixed the nanoparticles, which were 5, 10 and 20 nm in diameter, into the source-drain channel of the device using surface chemistry techniques and finished the structure by covering it with a 35 nm thick film of pentacene. The resulting device is called a nanoparticle organic memory field-effect transistor or "NOMFET".
Short-term plasticity

A biological synapse transforms a voltage spike (action potential) arriving from a pre-synaptic neuron into a discharge of chemical neurotransmitters that are then detected by a post-synaptic neuron. These are subsequently transformed into new spikes, leading to a succession of pulses that either become larger or diminish in size. This fundamental property of synaptic behaviour is known as short-term plasticity, which is related to a neural network's ability to learn. It is this plasticity that Vuillaume and colleagues have succeeded in mimicking.

In the NOMFET, the pre-synaptic signal is simply the pulse voltage applied to the device and the output signal is the drain current, explains Vuillaume. The holes – the charge carriers in the p-type organic semiconductor employed – are trapped in the nanoparticles and act like the neurotransmitters. A certain number of holes are trapped for each incoming spike voltage and in the absence of pulses, the holes escape in a matter of seconds

This time delay is carefully adjusted by the researchers by optimizing nanoparticle number and device geometry. "The output of the NOMFET is thus able to reproduce the deceasing or amplifying behaviour typical of a synapse depending on the frequency of spikes," said Vuillaume. _PhysicsWorld

Nanowerk story on NOMFET

More from ZDNet

H/T ScienceDaily

Such research is important in recreating the bottom-up behaviour of synapses, and eventually neurons and neuronal networks. It is not necessarily the best way to build an artificial brain, but important insights may arise from the work which will suggest better ways to build artificial brains.

Conceptualizing how the brain creates consciousness and intelligence would be a big help in the effort reverse-engineer the brain and to build machine intelligences. Unfortunately, every effort to do so up until now has been wrong. Not to worry. We do not have to be exactly right to achieve a meaningful result. Just approximately right -- and to be willing to double, triple, quadruple check our work and to start over again as often as we have to until we get it right.

If we become emotionally attached to a failed concept for too long, we miss our chance to achieve a useful tool.

Life is not about being "right" or winning a cocktail argument. It is about being effective and competent in getting things done. This superfluous culture of psychological neoteny and academic (and media) lobotomy will not last.


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