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Email You are free to share this article under the Attribution 4.0 International license. University University of California, Berkeley

Neuroscientists are building equipment to edit the sensations we feel, paste images we’ve never seen into our brains, insert non-existent scents into memory, and even cut out unwanted pain.

The researchers are using holographic projection into the brains of mice to activate or suppress dozens and ultimately thousands of neurons at once, hundreds of times each second, copying real patterns of brain activity to fool the brain into thinking it has felt, seen, or sensed something.

“The ability to talk to the brain has the incredible potential to help compensate for neurological damage caused by degenerative diseases or injury.”

The goal is to read neural activity constantly and decide, based on the activity, which sets of neurons to activate to simulate the pattern and rhythm of an actual brain response, so as to replace lost sensations after peripheral nerve damage, for example, or control a prosthetic limb.

“This has great potential for neural prostheses, since it has the precision needed for the brain to interpret the pattern of activation. If you can read and write the language of the brain, you can speak to it in its own language, and it can interpret the message much better,” says Alan Mardinly, a postdoctoral fellow in the University of California, Berkeley lab of Hillel Adesnik, an assistant professor of molecular and cell biology.

“This is one of the first steps in a long road to develop a technology that could be a virtual brain implant with additional senses or enhanced senses.”

Mardinly is one of three first authors of a paper in Nature Neuroscience that describes the holographic brain modulator, which can activate up to 50 neurons at once in a 3D chunk of brain containing several thousand neurons, and repeat that up to 300 times a second with different sets of 50 neurons.

“The ability to talk to the brain has the incredible potential to help compensate for neurological damage caused by degenerative diseases or injury,” says Ehud Isacoff, professor of molecular and cell biology and director of the Helen Wills Neuroscience Institute, who was not involved in the research project. “By encoding perceptions into the human cortex, you could allow the blind to see or the paralyzed to feel touch.”

Chunks of brain

Each of the 2,000 to 3,000 neurons in the chunk of brain was outfitted with a protein that, when hit by a flash of light, turns the cell on to create a brief spike of activity. One of the key breakthroughs was finding a way to target each cell individually without hitting all at once.

To focus the light onto just the cell body—a target smaller than the width of a human hair—of nearly all cells in a chunk of brain, they turned to computer generated holography, a method of bending and focusing light to form a 3D spatial pattern. The effect is as if a 3D image were floating in space.

In this case, the holographic image was projected into a thin layer of brain tissue at the surface of the cortex, about a tenth of a millimeter thick, though a clear window into the brain.

“The major advance is the ability to control neurons precisely in space and time,” says postdoc Nicolas Pégard, another first author who works both in Adesnik’s lab and the lab of coauthor Laura Waller, an associate professor of electrical engineering and computer sciences. “In other words, to shoot the very specific sets of neurons you want to activate and do it at the characteristic scale and the speed at which they normally work.”

The researchers have already tested the prototype in the touch, vision, and motor areas of the brains of mice as they walk on a treadmill with their heads immobilized. While they have not noted any behavior changes in the mice when their brain is stimulated, Mardinly says that their brain activity—which is measured in real-time with two-photon imaging of calcium levels in the neurons—shows patterns similar to a response to a sensory stimulus. They’re now training mice so they can detect behavior changes after stimulation.

Portable devices?

The area of the brain covered—now a slice one-half millimeter square and one-tenth of a millimeter thick—can scale up to read from and write to more neurons in the brain’s outer layer, or cortex, Pégard says. And the laser holography setup could eventually shrink to fit in a backpack a person could haul around.

As they improve their technology, they plan to start capturing real patterns of activity in the cortex in order to learn how to reproduce sensations and perceptions to play back through their holographic system.

Support for the work came from The New York Stem Cell Foundation, Arnold and Mabel Beckman Foundation, National Institute of Neurological Diseases and Stroke, McKnight Foundation, Simon’s Foundation Collaboration for the Global Brain, David and Lucille Packard Foundation, and Defense Advanced Research Projects Agency.

Source: UC Berkeley