by E. Paul Zehr
The idea of a human interacting with a virtual environment was also the central theme in some recent movies. In the 2009 Surrogates starring Bruce Willis, the basic theme is that remotely controlled robots are used as “surrogate people.” Eventually some users die when the robotic units they control are “killed.” I love one scene early on in the movie when a detective asks the police chief: “Sir, how is that even possible?” I bet you can guess the reply: “We don’t know.” Exactly. Anyway, the actions of the Iron Man suit were controlled by the brain activity of Tony Stark. Echoes of this story are also found in the 2009 blockbuster Avatar. The interface between the controllers and the Avatars is essentially a kind of biology-to-biology telepresence control and is very similar to an extreme extension of brain interface. The movie also shows the interesting biology-to-biology interface of Na’vi and the Pandoran wildlife. (The real fun part of Avatar is that we don’t yet have the technology for the mobile ride-inside exoskeletal robots that the military uses in that film.)
When I reread the stories about the telepresence armor in Iron Man #280–290 while researching this book, I was stunned by how closely they parallel the basic workings and operational theory of current brain-machine interfaces, although most of the real ones are one-directional. That is, they send commands to control a device but cannot necessarily receive commands from that device. Iron Man’s NTU-150, in contrast, was bidirectional and included information that couldn’t normally be picked up by human sensory organs.
The Interior Extremes of the Extremis Armor
With a bit of foreshadowing, let’s say for now that the Extremis armor comes the closest to what would be needed for the whole Iron Man concept to work with a real biological human body. By the end of this book, I hope to have convinced you of that. This concept is also the furthest away from reality of any of the armors developed so far. The Extremis armor that writer Warren Ellis created is a complete departure from everything that came before it. Not in terms of how it looks (see figure 1.2 and compare the panel C showing Extremis armor with panel B showing the classic red and gold armor), but in terms of how it interfaces with the user. We will talk in chapter 6 and elsewhere about the concept in perceptual neuroscience of “embodiment.” However Extremis takes a literal approach to embodiment, becoming part of the user’s body and allowing direct connection with the nervous system. The Extremis concept debuted with art by Adi Granov in the Invincible Iron Man story arc from 2005 and 2006 called simply “Extremis” and told in six parts. The origin story for Iron Man was updated for this series (Tony was now injured in the Gulf War rather than in Vietnam) and was collected in the 2007 graphic novel of the same name.
In this story, the basic idea behind Extremis lies in the work of Maya Hansen, a former girlfriend of Tony Stark and a scientist who tried to create a serum (described as a “powerful techno-organic virus-like compound” by Iron Man chronicler Andy Mangels) for a new supersoldier that became “Extremis.” A terrorist group steals this serum (actually, Maya gives it to them—long story). Eventually Iron Man fights Mallen, the leader of this group, who has been amplified by Extremis. Tony suffers debilitating injuries in this exchange and has to get Maya out of prison so she can help him undergo “extremis,” or a modification of his genetic expression (“rewriting the DNA”). In Tony’s case, the procedure creates a kind of amplified neural network that allows him to interface completely with his armor to directly jack in and control satellites and remote computers.
The gist of this story line is that Tony and the Iron Man armor are now biologically integrated. He is in fact a cyborg. But a cyborg who can effectively turn himself on or off. With Extremis, Tony Stark has the neural interface for his armor with him at all times. It sits as a layer of electronics just under his skin and in his bones. Extremis is fascinating scifion the very fringe of scientific fact.
Extremis represented a fundamental shift in how Iron Man was portrayed and really created a significant evolution for the character. Iron Man editor Tom Brevoort is quoted by Mangels as saying that, prior to Extremis, “Iron Man was a guy who had no powers and put on a suit, and when he was done, Iron Man was a guy that absolutely had some measure of powers outside of the armor, because the technology has become so integrated into him.” The questions central to our work here are, How much of these concepts are realizable? And if they are realizable—however incrementally—what does it mean for the human inside (or part of) the Iron Man suit of armor? To answer these questions means understanding a bit more about the characteristics of the human body, how it works, and what it means for the human body to be interfaced with technology. Next stop, on to looking at the basic biology of Tony Stark … and you!
CHAPTER TWO Building the Body with Biology
WHEN THE MAN OF METAL NEEDS TO MUSCLE IN
My transistors will operate the machine electronically—move countless gears and control-levers—the iron frame must duplicate virtually every action of the human body.
—Tony Stark to Professor Yinsen, from “Why Must There Be an Iron Man?” (Invincible Iron Man #47, 1972)
In motions honed to high efficiency by years of repetition, microcircuited metal mesh armor is slipped on, snapped into place and polarized to a hardness that rivals titanium steel, and once more a master inventor calls forth his greatest creation—Iron Man!
—“Dreadnight of the Dreadnought!” (Invincible Iron Man #129, 1979)
Iron Man in action—even just walking across a room—would turn heads in London’s Piccadilly Circus, New York City’s Times Square, or Tokyo’s Shinjuku train station. However, Iron Man wouldn’t be nearly so impressive if he could only stand stock still like a statue. Biological movement is based on the actions of muscles and, in vertebrates like us humans, those muscles are layered on top of our bony skeletons but underneath our skin. For Iron Man, the link between muscle activity and motorized actions of his mechanical exoskeleton has to be almost symbiotic.
Normally, when Anthony Edward Stark wants to make a movement, a chain of commands begins in his brain and finishes with the contraction of his muscles and the actions of his body. For example, think back to that excited reach you made to pull this book off the shelf and then carry it, full of hope, to the checkout line. (Or, for those of you so inclined, the motions you made to click on a computer to order it online. That’s cool, too.) When you decide to make a movement like lifting up your left hand, a series of commands are relayed from neurons in your brain, down to those in your spinal cord, and then out from the spinal cord to the muscles themselves to make them contract. That chain of command is an inherent part of Tony Stark’s and your nervous systems.
Muscles sit quietly inside our bodies, leaping into action only when we need them to do something. And, honestly, we need them to do something pretty much all the time. We humans have an awful lot of muscle in our bodies and they make up a whopping 40% of our total body weight. So, Tony Stark, whom Marvel Comics lists at about 6′1″ in height and about 100 kilograms (225 pounds), is packing about 40 kilograms (90 pounds) of muscle! You—and Tony—have three kinds of muscle in your body: smooth (like that found in your gut), cardiac (found in your heart only), and skeletal (found in the muscles that move your skeleton).
Skeletal muscle is probably the type you think of right away when someone shouts “muscle.” Your body has 639 skeletal muscles ready and willing to act during deliberate voluntary actions, during automatic activities like walking, and during reflex corrections to movements. The focus in this chapter is on how Tony Stark would use these muscles to help him control a fancy robotic suit of armor and on the chemical reactions that make these movements possible.
First, let’s look at some of the major muscles that are important for moving our arms and legs and giving us stability. In figure 2.1, panel A shows muscles on the front of the body and panel B shows muscles in the back. All 600-plus of these muscles will need to be protected and enhanced with the Iron Man suit. Of great importance is figuring out how realistic it m
ight be for Tony Stark’s nervous system to be linked to the muscles that move his body and to the suit that surrounds it.
Figure 2.1. Some muscles on the front (A) and back (B) of the human body. Images from Gray’s Anatomy modified by Mikael Häggström.
In such a suit the connection between brain and armor would need to be so good that the brain could actually control an instrumented robotic suit of armor, as if that suit of armor were a human body. In effect, Tony would have to create an anthropomorphic suit. That’s the same “anthro-” as in anthropology and means relating to things human. So, it must be a suit that is meant to look and act like a human. Such a degree of connection wasn’t needed in the first versions of Iron Man armor or even in the Iron Monger armor. For the level of interface between man and machine shown in recent comics, though, that type of suit would be needed.
To set up our exploration of this interface, we first look at how your own body is controlled. How does the nervous system work to produce movements? What kinds of signals are used and how does it all work together? The “motors” of your body are your muscles. In neuroscience the term “motor control” is used to describe how the brain controls movement. But real motors aren’t usually part of movement. Could muscle control be used to mimic the control of motors in a real machine? To answer these questions, let’s review the basics of biological activity and of the anatomy and physiology of the human body. This review will help us when we look at the topics of controlling robots, robotic exoskeletons, and similar inventions.
Muscles Alive! They Twitch! They Contract! They … um … Make Heat?
Let’s compare the overall structure and function of the limbs in our bodies to those of a robotic exoskeleton. The basic biological principle is that the bones of our skeletons support our bodies, the muscles move our bones, and our brains command our muscles. The sum of all the muscle activity and bone movement is the movement of our whole bodies. In the case of a robotic suit of armor, the new skeleton is on the outside and the “muscles,” in the form of motors or actuators, are on the outside of the new skeleton. So, we are dealing with two sets of supporting skeletons and two sets of muscles. For this whole enterprise to work, there has to be a link between these two sets. How that could possibly occur can best be understood by thinking through how the human nervous system functions. The cells of your nerves and muscles are what is known as “excitable tissue.” This refers to electrical excitability. Storing electrical activity of your cells is similar to the way a battery functions, except the “discharge” of your neurons powers information transfer instead of a flashlight or a Nintendo DS game. Which is pretty cool, in my estimation.
Nervous about Neurons
Neurons are excitable cells that generate and carry electrical signals. (Don’t worry. You will get a look at a neuron from the motor system in figure 2.3 later in the chapter.) The electrical signals result from an unbalanced concentration of ions on either side of the nerve cell membrane. Quite a lot is accomplished with just three household-sounding ions: potassium (K+), sodium (Na+), and chloride (Cl−). By the way, bananas, sweet potatoes, and halibut are all excellent sources of dietary potassium intake. You probably get most of your sodium and chloride in the form of table salt, NaCl. Other trace sources of chloride are olives, tomatoes, and celery, and sodium can be found in barley and beets. In addition to these three main players, you also have some special other ions inside your cells. Actually, these ions are found inside and outside of your neurons, but a dominant concentration is maintained in your cells by cellular pumps.
The cellular pump (or exchanger) is usually referred to by its biochemical name, Na-K ATPase. This cellular pump works in a similar way to a revolving door that helps move people inside and outside of a building. Put the potassium ions in the crowd moving in and sodium in the crowd moving out and you get the basic picture, with one twist. The Na-K ATPase revolving door doesn’t create equal opportunity openings. For every two K+ ions that are pumped in three Na+ are pumped out. As a result, at rest, sodium and chloride ions are much more highly concentrated outside your cells, while potassium is more highly concentrated inside. Because ions have either a positive or negative charge and they aren’t evenly distributed across the cell membrane, you wind up with an electrical difference between the inside and outside of the neuron. This is called the “membrane potential.”
A way to appreciate this potential difference is to think about a physical example. Imagine a tub of water. Now take a glass and put it into the water upside down so there is air trapped inside it. As you push it down into the tub, the glass will have some water enter it as the water pressure overcomes the air pressure in the glass. This is similar to the way that the membrane potential increases and decreases across your neurons. This changing level signals information flow in the nervous system. All cells have resting membrane potential differences, but it is only excitable cells in nerve and muscle that can generate changes in membrane potential and transmit those changes as information.
Muscles as Motors—How Do Tony Stark’s Muscles Work?
The spinal cord is highly organized. Sensory innervation of—or bringing nerves to—the skin on different parts of the body corresponds with different levels of the spinal cord. The relationship between nerves in the spine and what are called “dermatomes” is shown in figure 2.2. The organization of the dermatomes is typically thought of using the four regions of the spine and spinal cord. From head to “tail” these are cervical, thoracic, lumbar, and sacral. This concept of dermatomes is useful for diagnosis in clinical neurology. A good (bad?) example is with back injuries. If you or someone you know has had a disc herniation, they likely had some changes in how sensory information from the skin on the legs was relayed. For example, about 20 years ago I had three herniated lumbar discs at L3-L4, L4-L5, and L5-S1. As a nice reminder, I now have patchy sensation on the skin of my lower legs associated with the dermatomes for those spinal levels.
Activity in the nervous system leads to the activation of muscle. If Tony Stark decides he wants to pick up a laser-guided tool of some kind—maybe an arc welder—to make a modification to the Iron Man armor, a command will arrive at the motor cortex of the brain. This is the main movement-control area of his brain and the place where the commands that are sent down the spinal cord to trigger muscle contraction come from.
There is also the issue of motor innervations to “motoneurons”—short for motor neurons—for different muscles in the body. The motoneurons are also organized at anatomical levels. For example, when the signal descends to the part of the spinal cord where the nerve cells for the muscles involved in reaching are found, the cervical region in this case, activation of those cells commands the muscles to become active. For biological systems like your body, the lowest level of control for generating force is using what is called a “motor unit.” This unit is the nerve cell in the spinal cord and all the muscle cells (or fibers) that it connects with. So, when a muscle contraction occurs, it results from activity in many muscle fibers. The muscle fibers have proteins within them that regulate contraction and also produce the actual contraction forces. In figure 2.3, there is an example of a motor unit showing just a few muscle fibers. The motoneuron is at the top of the figure showing the cell body and dendritic tree (the filament-like bits at the top) in the spinal cord with the axon shown extending out to the muscle. The things that look like hot dog buns on the outside of the axon are the sheaths of fatty insulation called “myelin” that help keep signals moving quickly.
Figure 2.2. Dermatomes are areas of skin that are innervated—literally, supplied with nerves—by the sensory fibers from nerve roots in the spinal cord. Note that each dermatome is named according to the spinal nerve supplying it. Although there are seven cervical vertebrae, there are eight cervical dermatomes. Courtesy Ralf Stephan.
Figure 2.3. A motor unit—the basic functional unit for movement—consists of neurons (cell bodies) in the spinal cord, along with the extension of the axon out to th
e fibers in the muscle. Courtesy Johannes Noth (1992).
Once the electrical signal from a motoneuron arrives at the synapse (called the neuromuscular junction), that signal becomes chemical. The term “synapse” was first used by Sir Charles Sherrington, a Nobel Prize–winning physiologist (and, as readers of Becoming Batman already know, one of my superheroes of science). At the synapse for the neuromuscular junction, the chemical neurotransmitter acetylcholine is released, crosses the gap, and leads to depolarization of the muscle fibers. This turns the signal into an electrical one again and causes the release of calcium ions that serve as triggers for muscle contraction.