Brain Implants & Motor Paralysis: An Interview with Chet Moritz, PhD
Get a glimpse of Dr. Moritz’s research with brain activity and how it relates to fMRI studies, motor paralysis, and more.
By Douglas L. Beck, AuD
Academy/Beck: Good Morning, Chet. Thanks for meeting with me.
Moritz: Hi, Doug. Thank you, too, for your interest in our work.
Academy/Beck: My pleasure. Where and when did you get your doctorate?
Moritz: I earned my doctorate at the University of California at Berkeley in 2003.
Academy/Beck: Okay, great. Well let’s get right into it. I read about your work with Macaques monkeys and how you’re been able to re-route brain signals to move limbs. And thankfully, this didn’t involve long-term injury to the monkeys. Rather, you used chemical paralysis, much like we use in surgery every day, to disable the monkey’s arm, while inspiring the monkeys to move their hand to control a video game…but I’ll let you tell the whole story.
Moritz: Okay, here’s what we did. Our goal was to examine a potential treatment for motor paralysis, such as might result from motor vehicle accidents, sports injuries, and industrial accidents that lead to spinal cord injuries. We worked with monkeys trained to play very simple video games. The goal of the video game was for the monkeys to watch a screen and manipulate a cursor by hand to match a target box, and when they did, they received a reward such as applesauce. So after the monkeys knew how to play and enjoyed playing, we used a fast-acting neuromuscular blockade to temporarily anesthetize the nerves in the shoulder. Then, we recorded extracellular activity from single neurons in the monkey’s motor cortex using microwire arrays that were surgically implanted in the brain.
Academy/Beck: And just to clarify, I should add these are research animals. They have electrode arrays implanted in their motor cortex for years as the monkeys go about their day-to-day activities, and further, these electrodes are recording electrodes, so they’re serving a very different purpose from stimulating electrodes, such as those used with cochlear and brain stem implants, or retinal implants?
Moritz: Right. These electrodes are for recording and were implanted about one year earlier, allowing us to observe brain activity over time. These are high impedance, tungsten electrodes and they’re very selective, allowing us to record from one or several neuron cell bodies near the tip of the electrode. The diameter of the tungsten electrode is 50 microns.
Academy/Beck: So, that would be 50 one-millionths of a meter?
Moritz: Yeah, they’re pretty small! And they’re implanted about 3 to 5 millimeters into the cortex, allowing us to observe extracellular action potentials, or “spikes.”
Academy/Beck: And so the monkeys are awake, totally conscious, and they have temporary chemical paralysis on-board to prevent them from moving the controls using their hands, while at the same time, they really want to play the video games?
Moritz: Exactly. And so, as they attempt to move, or experiment with various strategies, their motor cortex is activated and we can record that activity that originates in their brain, even though it’s in the microvolt domain. We are recording and identifying timing of individual action potentials based on a characteristic electrical signature for each neuron. We can then use the timing, or rate of these action potentials to control electrical stimulation of the muscles of interest.
Academy/Beck: And as many new fMRI studies are finding, when people perform an activity such as singing or they think about singing, or playing guitar versus thinking about playing guitar, the same neurons in the brain are active during the recollection of the activity as in the performance of the activity.
Moritz: Yes, that’s right. And so when the monkey thinks about or attempts the activity, we can capture their electrical brain activity and send that activity through a device that stimulates the temporarily paralyzed muscles in the hand, allowing them to play the video game and get their reward, without having to send the signal through the spinal cord.
Academy/Beck: Amazing, and the application for this technology is astounding.
Moritz: Yes, the potential is fantastic and what we’ve done is actually a very simple demonstration of what might be possible for people with spinal cord injury. Of course, applying this to people with spinal cord injuries could be many years or decades away. So far we’ve only worked with up to two neurons at a time.
Academy/Beck: So in essence, this is a direct connection from brain-based neurons to peripheral muscles?
Moritz: Yes, that’s correct. So we’ve approached it a little differently. Others have gone about this sort of work by recording from many neurons and then de-coding the signal, and then recoding it to drive a robotic arm, or a computer cursor on a screen.
Academy/Beck: So this is a more direct way of facilitating volitional movement?
Moritz: Exactly. We used a simple linear equation that converts the rate of discharge from the neurons in the motor cortex to the amount of current delivered to the muscle. The electronics are so simple that they only take about the same amount of space as a cell phone.
Academy/Beck: So it boils down to a few circuit boards and batteries?
Moritz: More or less, yes. Similar technology has already been developed for functional electrical stimulation (FES) controlled by a shoulder switch and is currently in human use.
Academy/Beck: This really is amazing, Chet. What are your thoughts as to whether this represents neuroplasticity?
Moritz: Well, that’s interesting. I think it’s not yet clear as to whether this represents neuroplasticity at the synaptic level, or perhaps more of a behavioral-based re-learning. But either way, it would likely become automatic over the long-term.
Academy/Beck: Okay, Chet. Thanks so much for sharing your time and good luck in your follow-up and ongoing research.
Moritz: My pleasure, Doug.
Chet Moritz, PhD, is with the Physiology and Biophysics Department, University of Washington, in Seattle, Washington.
Douglas L. Beck, AuD, Board Certified in Audiology, is the Web Content Editor, with the American Academy of Audiology.