Imitating the brain, in silicon

Source:MIT

MIT researchers have created a semiconductor chip that is said to imitate how the brain’s neurons adapt in response to new information. With about 400 transistors, the silicon chip can simulate the activity of a single brain synapse — a connection between two neurons that allows information to flow from one to the other. The chip could also be used in neural prosthetic device research related to artificial retinas, says Chi-Sang Poon, a principal research scientist in the Harvard-MIT Division of Health Sciences and Technology.

Poon is the senior author of a paper describing the chip in the Proceedings of the National Academy of Sciences the week of Nov. 14. Guy Rachmuth, a former postdoc in Poon’s lab, is lead author of the paper. Other authors are Mark Bear, the Picower Professor of Neuroscience at MIT, and Harel Shouval of the University of Texas Medical School.

The researchers work relies on the their understanding of how a presynaptic neuron releases neurotransmitters, such as glutamate and GABA, which bind to receptors on a postsynaptic cell membrane, activating ion channels. Opening and closing those channels is said to change the cell’s electrical potential, sometimes strongly enough for the cell to fire 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,” according to an MIT press release.

The MIT researchers designed their computer chip so that the transistors could mimic the activity of different ion channels. This is an analog chip in which a gradient of electrical potential drives current to flow through the transistors just as ions are thought to flow through ion channels in a cell.

“We can tweak the parameters of the circuit to match specific ion channels,” Poon says. “We now have a way to capture each and every ionic process that’s going on in a neuron.”

The MIT researchers plan to use their chip to build systems to model specific neural functions, such as the visual processing system. Such systems could be much faster than digital computers.

Question: Do they actually understand how the brain works? Does this chip truly mimic that understanding? What good would it do if it did? What attempts failed before, and why?

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