Brain Connections that Last

Living electrodes could solve the lost-signal problem that plagues the science of mind-controlled prosthetic devices and electronics.

In a sci-fi-turned-reality future, we could be able to control devices with our thoughts alone. Researchers are working on it. Already, brain implants have been developed and tested in amputees and patients with paralysis who learn to move robotic arms, computer cursors, or their own arms via muscle and nerve stimulator with their thoughts along. While researchers, and their patients, have made immense progress, there is one problem that has nagged the field and slowed the otherwise fast pace of progress: over time, sometimes weeks, sometimes months, the implants stop working. They stop being able to receive messages from the neurons in the brain.

Researchers think they know why. The implant – usually a piece of metal that’s pushed into the brain to record signals from the neurons it touches – develops scar tissue around it that block the neuronal signals. Another problem is that the implants are not always so tolerant of the warm, wet, and salty environment of the brain and it appears that the delicate insulation surrounding the metal implants is broken down over time causing signal loss.

Now, Mijail Serruya, MD, PhD, a researcher at Vickie and Jack Farber Institute for Neuroscience at Jefferson is collaborating with the University of Pennsylvania to develop an intriguing solution to the lost-signal problem: a brain implant made almost completely out of neurons, a so-called “living electrode.” These neurons are grown inside a tube of hard jelly, or agar, the width of a human hair and then injected into the brain. The jelly protects the living electrode from immune cells that might otherwise create scar tissue and then dissolves over the course of a few weeks. And because they’re flexible and made from the same types of cells as the rest of the brain, they’re less likely to lose their connection to the brain signals they’re receiving.

Dr.  Serruya answers five questions about the ongoing work, recently described in Advanced Science News.

Q Where would the neurons for living electrode come from? How do we make sure it isn’t rejected like other foreign tissue?

A: For clinical applications, neurons could be created out of so called “induced pluripotent stem cells,” which are adult stem cells that can be taken from a blood sample and converted into other tissues, including neurons. This work is already being done at Jefferson: Professors Lorraine Iacovitti, PhD, and Piera Pasinelli, PhD, neuroscience researchers at the Vickie and Jack Farber Institute for Neuroscience at Jefferson, can take cells from a human being and turn them into neurons: this can be a lot easier than trying to retrieve cells directly from a patient’s brain. Since the cells are genetically the same as the patients’ other cells, they will not be rejected and will not require the use of immune-suppressive therapy.

Q How would the living electrode connect to the computer that interprets patient’s intentions?

A: There are several ways this can be done. One is to implant a tiny grid of metal electrodes under the skull, on the surface of the brain, where it is unlikely to encounter the same response as electrodes implanted deep into the brain. This lets the “living electrode” neurons “talk” with the rest of the brain and then convey that information to the grid at the surface of brain. The grid can then relay signals to external electronics and prosthetic devices. Another way would be to create “living amplifiers” that broadcast signals through the lining of the brain and skull to grids either implanted under the skin, or placed externally on the scalp, perhaps aligned with a magnet as is done with currently available cochlear implants that can restore a person’s ability to hear.

Q Since you’re putting in more neurons into a brain full of neurons, is there any risk that the neurons of the living electrode would become co-opted by the brain for other functions?

A: We want the living electrode neurons to be ‘co-opted’! We want the living electrode to integrate into the brain so it can both relay information out, and write information in. Just like cardiothoracic surgeons want porcine heart valves to be integrated into the tissues of a patient’s heart.

Q How is this different from injecting neuronal stem cells into the brain? Why do we need the agar tube?

A: Stem cells injected into the brain –or anywhere into the body- immediately migrate away, they don’t stay where they were injected. This is fine in certain circumstances (like a bone marrow transplant) but it won’t work if you want the neurons to serve as relays to the outside world via some other stationary device, such as a grid placed on the skin or implanted just under the skin.

Q Is it possible that someone could hack and control the external devices?

A: Living electrodes and conventional electrodes are no more or less “hack-able” than existing medical devices. Deep brain stimulators for Parkinson’s disease and cochlear implants for sensorineural hearing loss have been used for decades and have never been ‘hacked.’ In principle, any device with electronics—from a powered wheelchair to a pacemaker—could be ‘hacked’ it is just unclear what this really would afford the hacker that more direct methods could achieve more easily.

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