A team of Stanford University researchers has created a device that, once implanted in the brain, could help record movies of electrical neural activity in thousands of individual neurons.
The device, described in a paper published March 20 in Science Advances, could be used for research or with prosthetics, and is capable of recording more data while being less intrusive than other options.
"The design of this device is completely different from any existing high-density recording devices, and the shape, size and density of the array can be simply varied during fabrication. This means that we can simultaneously record different brain regions at different depths with virtually any 3D arrangement," Jun Ding, PhD, assistant professor of neurosurgery and neurology and co-author of the paper said in a Stanford News story. "If applied broadly, this technology will greatly excel our understanding of brain function in health and disease states."
At the heart of this invention is a bundle of microwires, each of which is less than half the width of the thinnest human hair. These wires, which are directed into the brain to obtain electrical signals that pass by, are small enough to cause minimal damage but sturdy enough to resist degrading over time.
The trick was figuring out how to design an orderly array of these super thin wires that is adaptable in terms of size -- some applications of the array may only warrant a few microwires but others would require thousands.
The researchers spent years designing and redesigning the device and the process for making it. Eventually, they found success by encasing each wire in a biologically-safe polymer, then bundling them in a metal collar. Below the collar, the polymer is removed from the wires so they can be inserted into the brain. Topped off with a silicon chip -- like those used in a camera -- the device can begin recording neural activity.
Once the researchers settled on their design, they were able to run tests in living tissues. They began with retinal cells from rats and a 138-wire array.
"We had to take kilometers of microwires and produce large-scale arrays, then directly connect them to silicon chips," Abdulmalik Obaid, a graduate student in materials science and engineering and lead author of the paper told Stanford News. "After years of working on that design, we tested it on the retina for the first time and it worked right away. It was extremely reassuring."
The team has also successfully tested the device in the brains of living mice, using arrays that ranged from 135 to 251 wires, and are continuing these studies so they can better understand the longevity of their invention and the kinds of signals it is able to obtain.
"Electrical activity is one of the highest-resolution ways of looking at brain activity," said Nick Melosh, professor of materials science and engineering and co-senior author of the paper. "With this microwire array, we can see what's happening on the single-neuron level."
Photos by Andrew Brodhead