Projecting a visual image directly into the brain, bypassing the eyes

Allowing the blind to see or the paralyzed to feel touch
July 14, 2017

Brain-wide activity in a zebrafish when it sees and tries to pursue prey (credit: Ehud Isacoff lab/UC Berkeley)

Imagine replacing a damaged eye with a window directly into the brain — one that communicates with the visual part of the cerebral cortex by reading from a million individual neurons and simultaneously stimulating 1,000 of them with single-cell accuracy, allowing someone to see again.

That’s the goal of a $21.6 million DARPA award to the University of California, Berkeley (UC Berkeley), one of six organizations funded by DARPA’s Neural Engineering System Design program announced this week to develop implantable, biocompatible neural interfaces that can compensate for visual or hearing deficits.*

The UCB researchers ultimately hope to build a device for use in humans. But the researchers’ goal during the four-year funding period is more modest: to create a prototype to read and write to the brains of model organisms — allowing for neural activity and behavior to be monitored and controlled simultaneously. These organisms include zebrafish larvae, which are transparent, and mice, via a transparent window in the skull.

UC Berkeley | Brain activity as a zebrafish stalks its prey

“The ability to talk to the brain has the incredible potential to help compensate for neurological damage caused by degenerative diseases or injury,” said project leader Ehud Isacoff, a UC Berkeley professor of molecular and cell biology and director of the Helen Wills Neuroscience Institute. “By encoding perceptions into the human cortex, you could allow the blind to see or the paralyzed to feel touch.”

How to read/write the brain

To communicate with the brain, the team will first insert a gene into neurons that makes fluorescent proteins, which flash when a cell fires an action potential. This will be accompanied by a second gene that makes a light-activated “optogenetic” protein, which stimulates neurons in response to a pulse of light.

Peering into a mouse brain with a light field microscope to capture live neural activity of hundreds of individual neurons in a 3D section of tissue at video speed (30 Hz) (credit: The Rockefeller University)

To read, the team is developing a miniaturized “light field microscope.”** Mounted on a small window in the skull, it peers through the surface of the brain to visualize up to a million neurons at a time at different depths and monitor their activity.***

This microscope is based on the revolutionary “light field camera,” which captures light through an array of lenses and reconstructs images computationally in any focus.

A holographic projection created by a spatial light modulator would illuminate (“write”) one set of neurons at one depth — those patterned by the letter a, for example — and simultaneously illuminate other sets of neurons at other depths (z level) or in regions of the visual cortex, such as neurons with b or c patterns. That creates three-dimensional holograms that can light up hundreds of thousands of neurons at multiple depths, just under the cortical surface. (credit: Valentina Emiliani/University of Paris, Descartes)

The combined read-write function will eventually be used to directly encode perceptions into the human cortex — inputting a visual scene to enable a blind person to see. The goal is to eventually enable physicians to monitor and activate thousands to millions of individual human neurons using light.

Isacoff, who specializes in using optogenetics to study the brain’s architecture, can already successfully read from thousands of neurons in the brain of a larval zebrafish, using a large microscope that peers through the transparent skin of an immobilized fish, and simultaneously write to a similar number.

The team will also develop computational methods that identify the brain activity patterns associated with different sensory experiences, hoping to learn the rules well enough to generate “synthetic percepts” — meaning visual images representing things being touched — by a person with a missing hand, for example.

The brain team includes ten UC Berkeley faculty and researchers from Lawrence Berkeley National Laboratory, Argonne National Laboratory, and the University of Paris, Descartes.

* In future articles, KurzweilAI will cover the other research projects announced by DARPA’s Neural Engineering System Design program, which is part of the U.S. NIH Brain Initiative.

** Light penetrates only the first few hundred microns of the surface of the brain’s cortex, which is the outer wrapping of the brain responsible for high-order mental functions, such as thinking and memory but also interpreting input from our senses. This thin outer layer nevertheless contains cell layers that represent visual and touch sensations.

Jack Gallant | Movie reconstruction from human brain activity

Team member Jack Gallant, a UC Berkeley professor of psychology, has shown that its possible to interpret what someone is seeing solely from measured neural activity in the visual cortex.

*** Developed by another collaborator, Valentina Emiliani at the University of Paris, Descartes, the light-field microscope and spatial light modulator will be shrunk to fit inside a cube one centimeter, or two-fifths of an inch, on a side to allow for being carried comfortably on the skull. During the next four years, team members will miniaturize the microscope, taking advantage of compressed light field microscopy developed by Ren Ng to take images with a flat sheet of lenses that allows focusing at all depths through a material. Several years ago, Ng, now a UC Berkeley assistant professor of electrical engineering and computer sciences, invented the light field camera.