by E. Paul Zehr
I had the opportunity to try out the Lokomat for walking retraining by visiting the lab of a colleague, Tania Lam, at the University of British Columbia in Vancouver, Canada. Tania and I are both part of the International Collaboration on Repair Discoveries (ICORD) based in Vancouver. Research at ICORD is all about discovering cures and restoring functions for people with spinal cord injury. Tania let me walk on her treadmill set-up with the assistance of the robot. Despite knowing quite a bit about how it works, having seen the Lokomat in use many times, I had never actually climbed in and given it a try for myself. You can see an example of what this device looks like in action in figure 5.3. It can move the legs in a walking pattern but needs the person to be hoisted up in a body-weight support harness system (looks a bit like a parachute harness). The figure shows me getting strapped into the device that will move my hips and knees while I “walk.”
Panel A shows me just getting the harness system on; in panel B you can see that the motor system (exoskeleton) is now strapped to my legs. In panels B and C I am just being lifted off the treadmill belt slightly (see my heels lifted), and in panel D I am actually being “walked” by the Lokomat robot. It can work as a kind of passive system, where I just relax and the Lokomat “steps my legs” for me, or it can assist my attempts to step. It can even be set to resist against my normal movements. It was odd when I tried to relax and let the robot step my legs for me. It was also very difficult to do.
Related to the use of Iron Man suit and aftereffects shown in figure 5.1, whenever I changed “modes” on the Lokomat—for example passive to active assist to resistance—it took a number of steps to adjust to the new condition and then several steps to get used to it again when we shifted to an older condition. I guess it would be similar to feeling what it was like to walk for the first time. Or like what it is like to walk in a new scenario, such as on an icy surface in the winter, a slippery wet area, or walking along a beach in strong surf. It takes a bit to adjust to (but you can do, of course) and then a bit to “unadjust” to.
Figure 5.3. The Lokomat robotic exoskeleton. I am suspended over a treadmill and using the exoskeleton to move my legs. Things are just starting in panel A. Notice in panel B that my heels are off the ground as the harness system takes up some body weight. Panel C shows the apparatus from the back, and I am actually stepping—or being stepped by the robot—in panel D. This equipment can be used to help with walking retraining after stroke and spinal cord injury. Courtesy Tania Lam.
Back in Iron Man’s world, Tony eventually reconfigures his armor so that, as described in “Yesterday … and Tomorrow” (Iron Man #244), “new servomotors and booster circuits move my legs for me! As long as I’m in this armor—I function as well as a normal man.” In this way the Iron Man suit was used to restore function that was lost, not just amplify function that Tony had. A point he clearly reflected on in “The Doctor’s Passion” (Iron Man #249) when he said, “Never thought there could be such pleasure in a simple phrase like, ‘I’ll walk.’ But after the time I spent in a wheelchair when I was shot, just putting one foot in front of the other seems like a miracle!”
A “Neuro”-plastic Iron Man
Tony’s recovery might be dramatic, but it is not actually miraculous. The experience the fictional Iron Man had is similar to what occurs in real life when the nervous system adapts to changes within the body. This is called “neural plasticity,” and we will encounter it numerous times in this book. The big theme in this chapter is the use of assistive technology to amplify performance, specifically in the context of amplifying Tony Stark’s abilities to produce Iron Man in action. But we are basing our discussion on examples of technology for real-life rehabilitation, such as devices like the Lokomat, which help retrain walking after spinal cord injury or stroke. This retraining of the body is directly related to neural plasticity.
Some time ago it was noticed that when a four-limbed mammal, like a cat, had a spinal cord injury that made it difficult to move, the back legs could be trained to walk again by stepping the legs on a treadmill. The animal then got better at walking. While the movement never becomes completely “normal,” it can be functional walking. This shows the ability of the nervous system to adapt and change. It is quite different from the concept of the nervous system being “hard wired” and unchangeable. Instead, the nervous system should be thought of as highly adaptable and changeable. Kind of hard wired with soft wire I guess! Going back to the specific example of walking, as in other mammals the brain and spinal cord coordinate our arms and legs together. There is strong evolutionary conservation in these connections and in the basic circuits in the brain and spinal cord that drive things like walking. We have collections of neurons called central pattern generators (or CPGs) that are evolutionarily conserved across all species, spanning the swimming lamprey, the crustaceans, the cat, the nonhuman primates, all the way to our own species of Homo sapiens. CPGs are networks of neurons in the spinal cord that can generate simple walking patterns. We humans have flexible linking of CPGs responsible for each arm and leg. This is what gives us our ability to perform a variety of movements like walking, running, cycling, and swimming. In my own clinical neuroscience research, we look at how we can tap into these connections that can be broken or lost in people who have had strokes or spinal cord injuries. It seems likely that portions of the connections coordinating arms and legs can be still active after damage in stroke. This probably means that the remnants of these neural pathways can be strengthened with training. A lot of work shows that this kind of locomotor retraining can improve walking even many years or decades after injury.
What was immediately obvious when I attempted to use the Lokomat was that it was very hard to walk at first when the walking was being done by something else. This is an important thing to think about for this and the next chapter. Try to make a list of the times that you performed a difficult movement task like walking or reaching and you didn’t actually have to do it for yourself. For most people such a list would be very short and might include no entries at all. My point is that usually when we want to do a movement we do it for ourselves. This means our brains are aware of both what we are trying to do and what actually happened. In contrast, when a robot moved my legs around during stepping, there was a mismatch between the sensory feedback that was occurring and my intentions for stepping, which were lacking. When these devices are used in rehabilitation of stepping in spinal cord injury, for example, it is likely that this disconnect is lessened. This is because there is already a separation in the relation between sensory feedback and motor output as a result of the injury.
This was shown clearly in the original origin story in Tales of Suspense #39 (1963) and revisited in “Why Must There Be an Iron Man?” (Iron Man #47, 1972). A panel from that story (figure 5.4) shows Tony talking about needing to learn how to walk again. This is a bit like the experience I had using the Lokomat. Except I didn’t have a full Iron Man suit. Or any kind of weapons, dang it. Anyway, this panel shows part of that disruption in coordination seen in figure 5.2. In that figure, the main concern was how coordination would be disrupted after taking off the suit or returning from spaceflight. However, coordination would also be disrupted when first putting the suit on (or walking initially with the Lokomat as I described above). In research studies this is sometimes known as walking in a “force field,” that is, when the normal movement of the body is restricted or resisted against. This is shown clearly when Tony says “I’m like a baby—learning to walk all over again.” Tony also says that “this armor’s circuits are coordinated with my brain waves,” which links back to our discussion of the Iron Man suit as a fancy neuro-prosthetic brain-machine interface. But what are the long-term effects of using the Iron Man suit on Tony’s nervous system? Above we talked about neural plasticity and recovery of walking using robotic exoskeletons after spinal cord injury. What happens if your nervous system is fine and you use a robotic exoskeleton anyway? What kind of plasticity occurs then?
As seen so far, the list of concerns for Tony is rather long and includes muscle atrophy, lowered bone mineral density, and loss of balance. Bottom line: he better not have too much strenuous work to do as Tony Stark unless he adheres to his training! Next let’s peek into his nervous system and see how things are going in there. We will find out that we will soon have to add brain remapping and recalibration of spinal cord pathways to his list of concerns.
CHAPTER SIX Brain Drain
WILL TONY’S GRAY MATTER GIVE WAY?
Hard … to move. Well, I expected that. This armor’s circuits are coordinated with my brain waves just as any living human’s brain controls his body…. I’m like a baby—learning to walk all over again.
—Tony Stark describing the original armor, “Why Must There Be an Iron Man?” (Invincible Iron Man #47, 1972)
Blast! I forgot that my command circuitry is more sensitive in this armor! I’ve activated a dozen systems with one thought! And what’s worse, they’re cancelling each other out! I’m not going—anywhere!
—Iron Man in space using prototype armor designed for extended periods outside earth’s atmosphere, “Sky Die” (Iron Man #142, 1980)
Stan Lee really likes the nickname “Shellhead” for Iron Man. What would it be like to “live” for a while within that real shell of iron? Here we take the next step in considering what would happen to Tony Stark’s body while inside Iron Man’s armor for long periods of time. Your body tends to adapt to things that happen to it. Even simple things like the sensations associated with wearing a new shirt or pants that may feel uncomfortable initially fade into the background with time. This is called “sensory adaptation.” Well, what sorts of sensory adaptation does Iron Man need to worry about? Or does he need to worry at all?
Let’s dig a little deeper into the brain. Earlier we talked about the arrangement—we called it a kind of “mapping”—of cells in the brain that control all the muscles of the body. Now, by map, I don’t mean a literal map or a picture like the homunculus shown in chapter 3. Instead I am talking about the direct correspondence between parts of the central nervous system and the muscles and other parts of the body. Because those neurons are directly involved in the brain control of movement, we called that the “motor map.” Producing effective commands for how and where we move is always informed by our senses, so it should be no real surprise that we also have sensory maps of the body. “Somato-” means “body” in Greek; these maps are called “somatosensory maps.”
These maps are present from birth and are refined based on what we experience in life. And, what an experience it would be for the nervous system to interface with a robotic device like the Iron Man suit of armor. The cells that have this representation in the somatosensory maps are found in the part of the brain known as the—as usual, please wait a beat and insert dramatic pause for scientific creativity—the somatosensory cortex.
Here’s a little thought experiment to help appreciate the extent of mapping of the brain cells in the somatosensory cortex. Imagine that you could record the activity of the neurons that are in that part of the brain. Now imagine that we are looking at the activity in the neurons of the brain receiving sensation from the skin of your left hand. Next, take your left index finger and tap it on the page that you are currently reading. The neurons of the cortex that are connected to the receptors in your left index finger that respond to touch would now be active. If you moved to a different finger, the same thing would happen to that brain area. You could continue to do this for all the skin areas on the body and you would create a (very distorted) map of the body. This is basically what the first scientists who did these kinds of experiments found. This mapping is now studied by using many different methods. One is to take many electrodes placed over the scalp in a form of electroencephalography, or EEG. Another is to record directly from the neurons themselves by putting electrodes directly into the brain or on the surface of the brain. Neurosurgeons distinguish areas that are meant to be operated on from those that aren’t by electrically activating the part of the brain in question. Then, using the sensations or movements that come from stimulating the correct (or more importantly incorrect) parts of the brain, areas for surgery can be mapped. You could also get this information on brain activity from scans taken with functional magnetic resonance imaging (fMRI), a powerful technique that includes both anatomy and the physiology of the cellular activity.
With all this in mind (pun intended), we have a decent idea about how information from parts of the body make their way into the brain. And this information can be captured as a kind of mapping representation of the body. What we really want to talk about here is the extent to which these representations can change. It stands to reason that maps that are created as a result of our experiences may be changed when our activities and experiences change. This is bringing us right back to the idea of neural plasticity that we talked about before in the motor system. Now we are in the sensory system, which is essential to consider if we want to comprehend how integrating the Iron Man suit of armor with Tony Stark’s brain could occur. It would not be enough for him to direct his armor to move with his brain. He would also have to be able to respond to stimuli in his environment.
An extreme example of Tony’s brain-machine interface is in “War Machine: Weapon of S.H.I.E.L.D., Part 1” (Iron Man: Director of S.H.I.E.L.D. #33, 2007), when Tony jacks into an entire satellite! Tony Stark’s trusty former driver and pilot Jim Rhodes is told, “Your armor hooks directly into the satellite. In effect, it’ll be an extension of you. A part of you. But you’ll be unaware of your body’s immediate surroundings.” The bit about how the satellite is is a “part of you” is something that comes up again later. Another example of what Tony Stark experiences with his direct neural interface armor is in the recent story lines found in “Invincible Iron Man” and penned by Matt Fraction. In “With Iron Hands, Part 3” (Iron Man: Director of S.H.I.E.L.D. #31, 2007), an interloper (Rahimov) who tries to use the Extremis armor is told by the computer that it is “compressing your cerebral cortex … bringing your neurons closer together … this will enable you to think more efficiently.” Well, I can tell you this won’t enable anyone to think more efficiently—your brain is already extraordinarily efficient.
Some Cranial Cartography: Malleable Maps in the Mind
To get the idea of how these somatosensory maps can change and how wearing and interfacing with a suit of armor might change the brain of a fictional Iron Man, let’s look at some real-life but surreal examples: face transplants and phantom limb pain. The idea of how we normally make use of sensation from movement is nicely captured by Tony Stark’s comments in “World’s Most Wanted: Part 1, Shipbreaking” (Invincible Iron Man #8, 2009). When reflecting on controlling the suit, Tony muses “trying to operate this suit without Extremis is like trying to fly six stealth bombers at once.” To connect with this, think about any of the times you have been temporarily disconnected from sensation in your nervous system—like when your leg or arm has “fallen asleep.” Recall what it felt like and how difficult it was when you tried to move around or do something ordinary like walking and you get a pretty good idea of how odd this sensation really is.
Usually picturing Iron Man involves linking a biological body to a robotic machine. A real-life example that may help us is when we try to link a human body with bits from another body. Don’t think Frankenstein but instead think reattaching an amputated finger or toe or transplantation of a limb or body part from a recently deceased donor. Or a partial facial transplant. In November 2005, a French woman named Isabelle Dinoire became the first person to receive a facial transplant. She had a horrible experience with her pet dog, who, during a long period while Isabelle lay unconscious on her floor, disfigured her by chewing and destroyed large port
ions of her face. She considered numerous options and decided to go with the pioneering approach of two surgeons, Bernard Devauchelle and Jean-Michel Dubernard of the Amiens and Lyon hospitals in France. After a grueling 15-hour surgery, Dinoire had a new face that had blood supply and sensation from her own body.
Beyond the staggering work involved in the procedure, the main reason to bring this up for our purposes is to imagine what this neural interfacing with a new face would feel like. According to a process known as “reinnervation,” nerves in the periphery will grow to targets at a rate of about 1 millimeter per day. Within six months, Isabelle Dinoire began to have sensation in her face. Both sensory reinnervation, to the skin for example, and motor reinnervation, to the muscles of the face controlling movement of the lips and cheeks, would continue occurring over time. It is striking to note that even five years after the procedure the sensation from the skin of the transplanted areas does not feel the same as her own skin. John Follain of the Sunday Times reported that she described to her physicians that the skin from the donor is “softer. I’m the one who can feel it.” This is despite the biological certainty that the skin itself isn’t actually softer. It just feels softer now to her. This is likely an outcome of the reinnervation of this new skin by the axons in Dinoire’s facial nerves. It also reflects the fact that even interfacing biologically similar but separate parts from another person into the body of someone cannot fully replace the normal intact connections. And instead can lead to odd sensations such as described by Dinoire.
