Brain Implants and Neuroscience: Interview with Chet Moritz PhD
Douglas L. Beck, AuD, spoke with Dr. Moritz about spinal stimulation, “intention to move” and more.
Academy: Hi, Chet. It’s great to speak with you again. Hard to believe it was five years ago when we last spoke about brain implants, motor implants, by-passing the spinal cord, and neuroscience! See interview from 2009.
Moritz: Hi, Doug. Yes, it’s been a while! Thanks for your continued interest in our work.
Academy: Thanks, Chet. For the readers not familiar with your work, if I were to summarize the most memorable aspects, I would say something like…You temporarily chemically paralyzed monkeys, rendering them unable to send an efferent signal from their brains to the their hands. However, you also placed electrodes along their sensory-motor strip, allowing you to record their cortical activity. At that point the specific cortical activity was selectively and digitally amplified, and sent to their forearm muscles via a computer, thereby initiating volitional motoric motion, while effectively bypassing their spinal cords. Is that a fair summary?
Moritz: Yes, that’s pretty much the idea and the goal was to see what we might be able to do with regard to helping people who’ve had spinal cord injuries or a peripheral nerve injury with resultant paralysis. So as you mentioned, we intercepted that bioelectric activity at the level of the brain and relayed it through a computer to the extremities. As such, when the monkey thought about moving their extremity, even though the natural neurologic signal were blocked, they were able to move that same extremity via our device.
Academy: And even though it’s been five years since we first talked about this and published it, it’s still quite amazing to me! Okay, so what’s the status quo in 2013?
Moritz: Well, it’s pretty exciting. Many of the components of our system have been updated and improved and other researches have begun to take the various components to clinical trial. For example, Brown University and Massachusetts General Hospital are performing a safety study and have implanted around five people with the brain recording electrodes we intend to use. Their focus has been on controlling cursors on a computer screen, and more recently controlling robotic arms. Even many years after a spinal cord or brainstem injury, their subjects are able to control devices in several degrees of freedom. This is important as we didn’t know previously whether the brain would re-map after paralyzing injuries, and the Brown group has done fantastic work to demonstrate that we can still extract the intention to move even after injury.
Academy: Please tell me a little more specifically about intercepting the “intention to move” in the absence of the anatomy and physiology which facilitates that motion.
Moritz: Sure, Doug. The thing is, when one plans, attempts, or actually creates an actual movement; similar populations of neurons in the brain are active. Some of these neurons indicate the direction, velocity and force of the desired motion and that activity can be “de-coded” and translated into the movement of a robotic arm or to control stimulation of paralyzed muscles.
Academy: And so it seems to me the starting point for the anatomic recording site is likely highly related to the anatomic correlates of the homunculus?
Moritz: Right. That’s almost always the starting point, and then of course, fine tuning goes on from there as some of those neurons will respond more robustly than others. Interestingly, the specific neurons chosen weren’t critically important in our initial study as the animals quickly learned to use even neurons not obviously related to movement.
Academy: Which speaks advantageously and inclusively with regard to the importance of neuroplasticity in your work, and obviously across all/most neurological rehabilitation?
Moritz: Exactly. Of course if we can intercept neurologic activity from a specific, desired area of the brain, that would be more convenient, but as you know Doug, form your work with cognition and audition, brains are incredibly flexible, and so we don’t have to locate or record from only the specific neurologic populations that originally controlled a given movement. .
Academy: That’s fantastic, Chet. And so just for grins, what’s the extracellular amplitude of these bioelectric signals?
Moritz: Well, depending on the distance from the neuron and the impedance of the electrode, the actual voltage will vary. Nonetheless, the peak-to-peak amplitudes are generally 50 to 250 microvolts. More importantly, however, is the firing rate of the neuron. That codes the digital information in the brain, and is the key feature that is used to drive muscle stimulation in our lab or robotic arm control done by others.
Academy: So the robotic arm research and development is being done by other researchers?
Moritz: Yes. That work is being done at Brown and also by a group in Pittsburgh. In Pittsburgh, they have recently demonstrated up to 7 degree-of-freedom robotic control, which is very impressive. Our work more recently has focused on stimulating the spinal cord below the injury. As you can imagine, electrically stimulating the spinal cord below the injury site has enormous advantages over stimulating the muscles directly, including reduced fatigue and activation of muscle synergies.
Academy: Right…but doesn’t neurologic and motoric atrophy which starts immediately in tandem with the injury, rendering the rest of the distal system dysfunctional?
Moritz: Well, that’s a great observation and a great question. In fact we just completed a study in rodents to investigate this issue. As it turns out, after a cervical spine injury (the most common spinal cord injury in people), stimulation of spinal cord below the injury is able to evoke a wide range of hand and arm movements beginning several weeks after injury. In addition, stimulation below the injury also confers a moderate but sustained therapeutic benefit that outlasts the stimulation. We published papers on both of these exciting findings earlier this year and we’ll place the references at the end of this interview.
Academy: Absolutely fascinating, Chet. Thanks so much for your time and thanks for the update.
Moritz: Entirely my pleasure, Doug. Thanks for your interest in our work.
Chet Moritz, PhD, is an assistant professor, in the Division of Physical Therapy, Departments of Rehabilitation Medicine and Physiology and Biophysics, Center for Sensorimotor Neural Engineering, and Program in Neurobiology and Behavior at the University of Washington.
Douglas L. Beck, AuD, is the Web content editor for the American Academy of Audiology.
For more Information, References, and Recommendations
Sunshine MD, Cho FS, Lockwood DF, Fechko AS, Kasten MR, Moritz CT. (2013) Cervical intra-spinal stimulation evokes robust forelimb movements before and after injury. Journal of Neural Engineering 10 (3).
Kasten MR, Sunshine MD, Secrist E, Horner PJ, Moritz CT. (2013) Cervical intra-spinal stimulation improves forelimb motor recovery after spinal contusion injury. Journal of Neural Engineering. 10(4).