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Plasticity. That is the term used to describe a key element deemed responsible for allowing our brains to learn, change and adapt. Researchers at MIT believe they have taken a major step toward replicating this important behavior in the silicon world.
While all of our processors today are digital, MIT has taken an abstract leap by creating a chip that is analog. The article notes that because of the way cells behave in the brain, it is difficult to mimic its functions with just binary ones and zeroes. The brain does not operate with simply "on" and "off" impulses but rather employs a gradation of those impulses where signals become strong and weak instead of black and white.
To understand what the researchers have achieved, one must understand the basic, underlying principles behind how neurons behave. MIT outlines some of the basics here:
"There are about 100 billion neurons in the brain, each of which forms synapses with many other neurons. A synapse is the gap between two neurons (known as the presynaptic and postsynaptic neurons). The presynaptic neuron releases neurotransmitters, such as glutamate and GABA, which bind to receptors on the postsynaptic cell membrane, activating ion channels. Opening and closing those channels changes the cell’s electrical potential. If the potential changes dramatically enough, the cell fires an electrical impulse called an action potential.
All of this synaptic activity depends on the ion channels, which control the flow of charged atoms such as sodium, potassium and calcium. Those channels are also key to two processes known as long-term potentiation (LTP) and long-term depression (LTD), which strengthen and weaken synapses, respectively."
Because of this advancement, researchers can now mimic the behavior of a neuron in its entirety by controlling the flow of electricity through transistors to simulate ion channels found in cells, a feat not possible with previous attempts at creating "brain-like" chips. MIT claims that with about 400 transistors, the chip can approximate the function of a single synapse. Synapses are the connections between neurons that allow the flow of data which, in simple terms, allows for computation.
Scientists have put the chip to use and already believe they have solved a long standing debate. Utilizing the new technology to create a seemingly accurate model, researchers can demonstrate how LTD (long-term depression) ocurrs. "Nobody had put all this together and demonstrated computationally that indeed this works, and this is how it works," claimed Chi-Sang Poon, the senior author of a paper describing the chip and a principal research scientist at MIT.
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