Editor’s Note (04/27/18): With today’s release of Marvel’s new movie "Avengers: Infinity War," Scientific American is resurfacing an August 2014 story that delved into the neuroscience behind the Hulk, Captain America and Iron Man.

The job of creating superheroes has become more complicated in the 50-plus years since Marvel Comics first assembled the Avengers to fight evil. Audiences today still crave fantastical adventures but at the same time demand a greater degree of plausibility. In response Marvel and Victory Hill Exhibitions gathered a real-life team of scientists to ensure that its Avengers S.T.A.T.I.O.N. Exhibition currently on display in New York City’s Times Square includes elements of realism as it explores Marvel’s superhero mythology.



Beyond simply being a colossal advertisement for its brand, the exhibit enables Marvel to delve into the neuroscience behind Dr. Bruce Banner’s metamorphosis into his green alter ego as well as Capt. Steve Rogers’s transformation into a supersoldier. Another key exhibit mimics the heads-up display that billionaire industrialist Tony Stark uses in his Iron Man suit.



The general public has become more educated about science, so Marvel has had to work harder to come up with explanations that allow the audience suspend disbelief, says neurobiologist Ricardo Gil-da-Costa, a science advisor for Marvel’s Agents of S.H.I.E.L.D. TV program. Gil-da-Costa, whose company Neuroverse consulted on aspects of the exhibition related to neuroscience and helped build Iron Man’s heads-up display demonstration, began speaking with the Avengers S.T.A.T.I.O.N. creators two years ago in an effort to craft the right mix of entertainment backed by real science.



The Hulk

The Hulk’s legend has grown in the half century since Marvel introduced his character, best known for smashing, grunting and shredding Bruce Banner’s wardrobe. Much less is known about the neurological transition that the physicist’s brain undergoes each time he transforms from an articulate 58-kilogram man into the 470-kilogram green brute. Exhibit makers determined that the Hulk in particular provided a unique opportunity to help young visitors understand how the human brain works. The first step was to evaluate the green superhero’s powers and “reverse engineer” some of them back to their neurological roots, Gil-da-Costa says.



The Hulk demo within the sprawling, 930-square-meter S.T.A.T.I.O.N. exhibit begins with an actual MRI scan of a human brain that represents Banner’s gray matter. Simulation software portrays the anatomical changes that the doctor’s brain undergoes as he becomes the Hulk.

“The angrier Hulk gets…”

Supervillains know, or at least they should by now, to take cover when the Hulk starts his rampage—his strength is directly proportional to his level of rage. Banner’s conversion from a mild-mannered scientist to his superhero persona results in a 20 percent growth in his amygdala, coupled with a 30 percent reduction of the prefrontal cortex, which decreases his ability to control rational reflection and decision-making. This change is responsible for the Hulk’s highly emotional behavior, during which he typically reacts with impetuous emotions rather than lucid thought. The amygdala, a small, almond-shaped structure located deep in the lower part of the temporal lobe, is associated with the processing of emotions and contributes to memory formation. The prefrontal cortex, meanwhile, receives information from other brain areas to perform cognitive processes like problem solving, prediction of outcomes, decision-making and behavioral planning.



“Hulk is going now! Don't try to follow!”

The Hulk is capable of incredibly long leaps, as far as 1,600 kilometers by some estimates. To cover such distances and land in the right spot, the Hulk needs rapid and increased visual processing while moving at high speeds, Gil-da-Costa says. To do this the visual cortex in Banner’s brain grows about 15 percent in size when he becomes the Hulk, enabling him to better perceive, discriminate and structure what he sees. Likewise, a 50 percent growth in Banner’s cerebellum—fundamental for motor control, equilibrium, coordination and timing—helps give the Hulk the balance, spatial processing and precision he needs to land on his big, green feet.



“Hulk smash!” (Well, “smashes”)

Hulk has also been known to lay waste to the English language. That probably has to do with the 25 percent reduction in Banner’s planum temporale, which changes his brain’s capacity for language and causes the Hulk to lose the ability for fluent speech, according to Gil-da-Costa. The planum temporale is highly asymmetric—larger in the left hemisphere—a characteristic thought to be part of the human evolution to specialize brain areas for language. A computer simulation at the exhibition shows that Banner’s brain loses this asymmetry when he gets Hulked up.



Captain America

Unlike Hulk’s repeated transformations Steve Rogers’s conversion into Captain America occurred only once and produced mostly positive benefits, including strength and agility, without affecting his capacity for reasoning or language. The supersoldier serum that Professor Abraham Erskine injected into Rogers actually led to increased neural connectivity between brain areas that he frequently activates. In his case, the amygdala, orbitofrontal cortex, prefrontal cortex and visual cortex as well as the motor, pre-motor and somatosensory regions. Working together this network of brain areas processes aspects of a person’s understanding of what others are feeling, in other words aspects of empathy and concern for others, Gil-da-Costa says.



Gil-da-Costa and his team posit that Captain America’s superhuman hand–eye coordination, reflexes, motor speed and muscle response could be side effects of the increased connections between visual cortex and premotor and motor areas.



A phenomenon called synesthesia—a neurological condition of increased connectivity between brain areas in which stimulation of one sense automatically activates a second sense—was also part of the inspiration for Captain America’s brain. People with this condition “hear” colors, for instance. “Captain America doesn't have synesthesia per se, but the same underlying phenomena of increased connectivity occur,” Gil-da-Costa says. “So, it was an inspiration for the designing his brain and structuring it in real science.”



Iron Man

Tony Stark’s enhanced abilities come from neural prosthetics in his metal suit rather than actual changes to his brain. Stark activates different areas of his suit using, amongst other things, a brain–computer interface that converts his brain signals into instructions that his suit’s computer uses to control its flight and fire weapons as well as work the heads-up display (HUD), which gives Iron Man precise information about his surroundings.



To simulate Iron Man’s HUD at the Avengers S.T.A.T.I.O.N. Exhibition, Neuroverse developed a novel electroencephalographic (EEG) brain–computer interface powered by the low-voltage electrical activity that enables brain cells to communicate. This three-electrode EEG is connected to a small display screen. The interface activates when visitors press their foreheads against the EEG sensor, which detects brain waves and converts these signals into commands that the on-screen HUD simulation follows. This technology, integrated with an additional eye-tracking system from The Eye Tribe, allows visitors to navigate the display to watch video clips, play games and see a graph depicting their neural activity in real-time.



The development an accurate EEG-based brain–computer interface that would work for the exhibit’s large and constantly churning audience proved particularly challenging. Exhibit creators developed specific hardware related to sensing the brain and algorithms to interpret an individual’s brain signals. This software requires some degree of recalibration when a new visitor engages the exhibit because each person’s brain and thought patterns—even in response to the same stimuli—are unique. Neuroverse’s sensor begins to take readings when a forehead is pressed against it. This also serves to keep the person’s head fairly still so that the system can more easily read brain waves.



Marvel’s Avengers S.T.A.T.I.O.N. Exhibition is on display through January 4, 2015. Neuroverse is working on a small, multi-use wireless brain–computer interface for use in everyday life. That system is expected to be a low-cost mobile device for monitoring various types of neural activity and sharing that information via a smartphone app.