Slightly larger than a kumquat, the insula is part of the cerebral cortex, the thick folds of gray tissue that form the brain's outer layer. The densely rippled structure sits on the inside of the cortical mantle, resembling a tiny Japanese fan tucked neatly into the brain's interior. It is commonly thought of as the seat of interoception, or the sense of your body's internal state.
The insula generates this sense by maintaining a map of all your far-flung organs and tissues. Certain neurons in the insula respond to rumblings in the intestines, for example, whereas others fire to reflect a toothache. To manage the influx of messages bombarding it from throughout the body, the insula collaborates closely with the anterior cingulate cortex, an area crucial for decision-making, to evaluate and prioritize those stimuli. This raw representation of bodily signals has been hypothesized for more than a century to be the origin of emotions.
At first glance, pegging the insula as critical to anything can seem almost meaningless. It has been implicated in functions as diverse as decision-making, anticipation, timekeeping, singing, addiction, speech, even consciousness. The insula and the anterior cingulate cortex are the most commonly activated regions in brain-imaging experiments, according to a 2011 study, making it all the more difficult to discern their core functions.
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.