New ‘Artificial Synapse’ Gets Closer to Mimicking Brain Connections

The so-called memristor, an electrical component whose resistance relies on how much charge has passed through it in the past, mimics the way calcium ions behave at the junction between two neurons in the human brain, the study said. That junction is known as a synapse.
The researchers said the new device could lead to significant advances in brain-inspired, or neuromorphic, computers, which could be much better at perceptual and learning tasks than traditional computers, as well as far more energy efficient.
"In the past, people have used devices like transistors and capacitors to simulate synaptic dynamics, which can work, but those devices have very little resemblance to real biological systems.
So it’s not efficient to do it that way, and it results in a larger device area, larger energy consumption and less fidelity," said study leader Joshua Yang, a professor of electrical and computer engineering at the University of Massachusetts Amherst. [10 Things You Didn’t Know About the Brain]
Previous research has suggested that the human brain has about 100 billion neurons and approximately 1 quadrillion (1 million billion) synapses. A brain-inspired computer would ideally be designed to mimic the brain’s enormous computing power and efficiency, scientists have said.
"With the synaptic dynamics provided by our device, we can emulate the synapse in a more natural way, more direct way and with more fidelity," he told Live Science. "You don’t just simulate one type of synaptic function, but [also] other important features and actually get multiple synaptic functions together."
In biological systems, when a nerve impulse reaches a synapse, it causes channels to open, allowing calcium ions to flood into the synapse. This triggers the release of brain chemicals known as neurotransmitters that cross the gap between the two nerve cells, passing on the impulse to the next neuron.
The new "diffusive memristor" described in the study consists of silver nanoparticle clusters embedded in a silicon oxynitride film that is sandwiched between two electrodes.
The film is an insulator, but when a voltage pulse is applied, a combination of heating and electrical forces causes the clusters to break up. Nanoparticles diffuse through the film and eventually form a conductive filament that carries the current from one electrode to the other. Once the voltage is removed, the temperature drops and the nanoparticles coalesce back into clusters.
Because this process is very similar to how calcium ions behave in biological synapses, the device can mimic short-term plasticity in neurons, the researchers said. Trains of low-voltage pulses at high frequencies will gradually increase the conductivity of the device until a current can pass through, but if the pulses continue, this conductivity will eventually decline.