Nevertheless, the case for the insula as the hub of athleticism has been building slowly for more than a decade. In the late 1990s neuroanatomist A. D. Craig at Barrow Neurological Institute was mapping the pathways that deliver pain and temperature sensations to the brain through the spinal cord. Upon discovering that these conduits led to the insula, he posited that one of the brain's core functions is to help the body maintain homeostasis, or equilibrium. For example, the body's internal temperature usually stays within a narrow range, and perturbations, registered by the insula, motivate us to restore it to that comfortable zone—perhaps by drinking cool water, seeking a shady patch or ceasing movement. Indeed, when scientists damaged the insula in rats, their ability to regulate their bodies was impaired.
When we exercise, we agitate our internal state. "Everything we do requires a calculation of how much energy it costs us, and this is what the insula seems to be performing," Craig says. By predicting how certain exertions will affect the body, the brain can initiate actions to temper those perturbations before they happen.
A compelling study from 2004 showed clear anatomical differences that matched variation in interoceptive ability. Hugo Critchley, now at the University of Sussex in England, asked participants to estimate the rate at which their hearts were beating without taking their own pulses. The people who guessed their heart rates most accurately had greater activity in the insula and more gray matter in this region. That last point is crucial, because it suggests that the physical size of the insula is directly related to differences in ability. This neural imprinting is similar to what is seen in professional violinists, whose motor cortex devotes greater real estate to the representations of fingers than is seen in an amateur's brain.
The OptiBrain researchers hypothesized that athletes need to be intensely aware of sensations such as heartbeat—and capable of recognizing the important ones and dismissing the red herrings. "The vast majority of NBA players are amazing athletes. But some of them stand out. It's not that Kobe Bryant or Derrick Rose has more energy, it's how they choose to expend that energy in critical moments that will decide their success," clinical psychologist Alan Simmons at the Veterans Affairs San Diego Healthcare System says.
To test the idea that extremely fit individuals have superior interoception—and to investigate what this superiority looks like in action—Paulus and Simmons recently recruited a group of elite athletes to lie in a scanner and perform cognitive tests while an apparatus restricted their breathing. The feeling of shortness of breath is an unpleasant sensation that is known to rev up the insula.
Paulus and Simmons tested 10 of the world's most accomplished adventure racers—men and women who perform wilderness challenges that can include climbing, swimming, running and paddling. They asked the racers and 11 healthy control subjects to lie in a scanner and breathe through a tube while wearing a nose clip. While in the magnetic resonance imaging (MRI) machine, the subjects were instructed to view arrows pointing either left or right on a screen and press a button to note the direction. Sporadically, the researchers adjusted the airflow so that breathing became significantly more difficult. A change in the screen's color alerted the participants that breathing was about to become labored. The color change did not always accurately predict breathing restriction, however.
In all phases of the experiment, the insula was active, but to varying degrees. The healthy volunteers performed equally well on the arrow tests throughout the study—with no interference, when the screen’s color changed and when struggling to inhale. But the adventure racers got more answers correct when either anticipating or undergoing the breathing load. Perturbing these individuals' interoceptive experience actually improved their performances. The racers also showed more brain activation when anticipating the breathing restriction but not while experiencing the restriction itself. It was as if the racers' brains made better use of cues to prepare themselves, thus gaining a cognitive edge. When the challenging moment arrived—when their breathing became labored—their insulas were comparatively placid.
Another study from Paulus's group, also published in 2012, adds nuance to this finding. The group sought to investigate elite athletes' cognitive flexibility. Considered a landmark of intelligence, this skill involves switching easily between opposing demands. Mental agility can plummet in a trying situation, however. Experiments on Navy SEALs and Army Rangers revealed that exposure to combatlike conditions impaired their reaction times, vigilance, learning, memory and reasoning. For Olympic-level athletes, too, grace under fire is a major objective.
To observe cognitive flexibility in action, Simmons asked 10 Navy SEALs and 11 healthy male civilians to perform a simple task in a brain scanner. Navy SEALs are extremely athletic individuals who are trained to cope with great demands on their physical, mental and emotional faculties. The exercise involved observing either a green or red shape followed by an emotionally laden photograph on a screen. Participants were to press one button when they saw a circle and another when they viewed a square. A green shape signaled that a positive image (such as a child playing) would follow; a red shape indicated that a negative picture (for example, a combat scene) would appear next. The subjects were then judged on their speed and accuracy in identifying the shapes.