Zoobiquity (5 page)

It’s a grim irony that the one group of people who may best understand the vital role fainting plays in giving the body a needed respite is a group dedicated to inflicting pain: torturers.
Many narratives taken from torture victims contain a nauseatingly familiar refrain. Under the terror and physical violation, many victims pass out. But, horrifically, when they come to, the torturer is cued to resume his assault. You could say that by overriding the body’s protective response—the faint—the torturer adds yet another level of affliction, the way sleep deprivation keeps a body from having a restorative break.
^‡

A slowed heart offers another key survival advantage. It helps a vulnerable animal keep still.
Canadian scientists studying white-tailed deer tracked what happened when they played recorded wolf howls to fawns. The baby deer responded with “very predictable” alarm bradycardia, slowing their hearts and quieting their bodies. Think of the survival edge this physiological trick gives to fawns, who often get left alone for long periods while their mothers go off to forage. A slowed heart rate keeps them from rustling around when danger is nearby. In other words, it helps them hide. Is this physiology present in young humans?

This is the kind of experiment we would never do on infants; terrifying them on purpose to test their heart rates would certainly get the researcher excoriated, if not arrested. And yet, remarkably, an accident of geopolitical fate has given us a small window into how the very youngest members of our own species respond to primal terrors.

On the night of January 18, 1991, during the Gulf War, Scud missiles launched by Iraqi troops began exploding in Israeli communities. Citizens were alerted by howling air-raid sirens that blared from outdoor speakers and on the radio and TV. Since there was a terrifying possibility that the bombs were carrying chemical payloads in addition to their explosive power, the frightened populations had been instructed to don gas masks and seek shelter when they heard the wail of a siren.

In the maternity ward of a Tel Aviv-area hospital that night, three women were in labor. As is standard practice, they had been fitted with fetal heart monitors that strapped around their bellies to keep track of their babies’ heartbeats. At three a.m., a sudden, terrifying shriek of a Scud alert siren penetrated the walls of the maternity ward—and, apparently, the wombs of the expectant mothers. As hospital staff scrambled to put gas masks on themselves and their patients, the nurses noticed something highly unusual on the fetal monitors. The heart rates of all three of the about-to-be-born infants suddenly and unexpectedly.
… plummeted
. From a healthy and brisk 100 to 120 beats per minute they slowed by half, to a frightening 40 to 60. The tiny hearts “lay low” like this for two minutes and then returned to normal.

All three babies, who hadn’t yet even heard their parents’ voices outside the womb, responded physiologically, with bradycardia, to the sound of danger. Some of the slowing may have resulted from the sounds of the siren itself and some from maternal stress hormones entering the fetus’s body in response to the siren. Either way, these obstetrical observations strongly suggest that even prior to birth itself, we’re equipped with unconscious anti-predator defenses, including a potent alarm bradycardia response. All three babies were ultimately born healthy, as well as apparently armed with the full complement of survival instincts we all possess but rarely think about.

Hiding in the face of danger—what scientists call crypsis—is one of nature’s most common and effective strategies for staying out of a predator’s stomach. Some animals depend on body shapes and camouflage to help them hide. And some conceal themselves by performing instinctive or learned behaviors like freezing, hiding, or crouching. Many animals do all of these. The stillness of a slowed heartbeat is just one of many tools prey animals employ to help them “disappear,” at least as far as a predator is concerned.

Freezing, hiding, and crouching—with the help of slowed hearts—connect our nervous systems to the vast range of species with whom we share common ancestry. Examining fainting through the lens of veterinary medicine allowed me to reframe this common but puzzling cardiac event as a possible anti-predation strategy. And this hypothesis, in turn, helped me understand the powerful feedback loop between heart and brain that results, for some of us, in lost consciousness or passing out. Exploring why took me into the watery habitat of our ancient ancestors.

Astronotus ocellatus
, commonly known as an oscar, is a freshwater fish related to tilapia. Energetic and affectionate, oscars’ reputation as “puppies of the aquarium” comes from the enthusiastic greetings they give their owners, complete with tail wagging, acrobatic flips, and finger nibbling.
But when oscars get stressed out—for example, when you’re cleaning their tank—they can seemingly go lifeless. Lying on their sides, completely still, they lose color and breathe more slowly. Their fins stop moving. They sometimes stay this way even when nudged.

If I were able to place an aquatic version of my stethoscope over the heart of that very still—yet alive—fish at the bottom of the tank, I would hear another clue as to why fainting may have survived so many grueling rounds of natural selection. Or, rather, the clue would be in what I
wouldn’t
hear: a robustly beating heart. Instead, I’d notice the familiar, super-slow rhythm of a bradycardic heart, dominated by lengthy pauses between beats.
^§

To understand the significance of this decelerated, less noticeable heart rhythm, consider the physiology of a master predator: the shark. Along with certain other underwater predators, like rays and catfish, sharks come equipped with heartbeat
detectors
.
Called ampullary organs, these specialized sensory cells pick up the weak electrical pulses put out by the beating hearts of other fish. The hunters’ internal ears may also scan for fish heartbeats, picking out the
lub-dubs
like doctors do through stethoscopes. Predators can lock onto the telling signals and home in on them
with lethal accuracy, even when their target is some distance away or hiding under sand. Which means: underwater, a beating heart can be a deadly giveaway.
^‖

Every one of us has this “tell.” Whether you’re a human being, a salamander, or a canary, your telltale heart starts beating in the early days after conception and keeps going until the day you die.

But if a fish underwater could silence its beacon, it would become acoustically invisible. It might even be able to evade a predator. Anyone who’s seen a submarine movie will recognize this principle. The commander of a submarine being tracked by enemy sonar will invariably order his crew to “run silent”—which involves everything from shutting off radios to cutting the engine to suppress the heartbeat of the submarine. Once the threat has passed, they fire up the engines again and the sub speeds away to safety.

Knowing this, we can see why natural selection might have favored fish that had the good fortune to faint their way out of becoming dinner. Having a heart that radically slows in response to real or perceived threats might have been a major advantage, offering protection before an attack even got under way. Fainting and “near fainting while conscious” may have evolved as a lifesaving “third option,” offering a protective alternative to the more storied “fight or flight.”

As we know, the heart-slowing reflex triggered by states of high arousal, such as fear, pain, or distress, is a core feature of vasovagal fainting in human beings. Alarm bradycardia has protected animals across all classes of vertebrates, and persists in us today precisely because its protective power is so deeply embedded into the autonomic nervous system, which has been passed down from our ancient water-dwelling ancestors. This hypothesis connects the acutely slowing heart of a hunted fish in the water to a human fainter in the ER.

In some ways, it’s hard to think of ourselves as prey. Human beings today are so dominant on our planet that we can (and do) wipe out whole species, sometimes without even knowing it. Most of us in developed countries will make it through our entire lives without ever facing a realistic threat from a nonhuman animal predator. An evolutionary
vestige like fainting seems as ill-fitted to our modern times as a chariot repair shop. But a zoobiquitous approach lets us understand reflexes and behaviors in ourselves that mirror anti-predation strategies in other animals.

Picture the myriad defenses nature has bestowed on many adult animals: quills, antlers, talons, noxious smells, and deadly poisons. While all can be useful during an attack, they also serve as “don’t mess with me” warnings that can prevent an attack in the first place.
The same goes for a peculiar jumping maneuver among deer and gazelles called “stotting.” The stotting animal springs up, lands stiffly on all four legs, then springs up again and again, moving away from a predator as if on a pogo stick. Scientists argue about how this behavior helps an animal escape. It seems like a colossal waste of energy—energy that could be spent on running away. But the whole point seems to be to show off superb stamina. Stotting tells a predator that the animal has energy to spare and even
thinking
about giving chase is a waste of time.

Wildlife biologists call these physical traits and behaviors “signals of unprofitability.” They send a clear message to a predator: Move along, find an easier target.

We humans use signals of unprofitability for protection, too. Picture a bodyguard flexing his bulging biceps. Think about how you might instinctively pull yourself up to your full height and walk with an exaggerated swagger on an unnervingly quiet street at night. Imagine the sign on your lawn advertising that you have a burglar alarm inside, or the teams of lawyers employed by big companies to fight lawsuits. The message in each case is the same: Find another victim. This one’s too much trouble.

Indeed, maintaining and advertising a strong defense is a fundamental drive across species. In a conversation I had with the late Harvard evolutionary biologist Karel Liem, he explained that nearly every animal behavior has elements of self-protection, or anti-predation, at its core.

And the physiology of fainting is no different. Simply being still can confer survival advantages. Of course, it doesn’t always work, but it does enough of the time to make it a respectable option of last resort.

Yet respect is rarely the reaction that greets fainters. Alarm bradycardia, vagal nausea, freezing in place, feigning death, and full-on fainting are almost always taken as signs of weakness or cowardice, portrayed in literatura
and film as shorthand for the lily-livered. Franklin Pierce’s episode of battlefield fainting, for example, landed him the moniker “the Fainting General,” which dogged him even after he became president of the United States in 1853. Few would characterize George H. W. Bush, Margaret Thatcher, David Petraeus, Fidel Castro, or Janet Reno as weak-willed, yet all suffered fainting spells while in office. To an observer, passing out might seem helpless, a physiologic act of surrender, even defeat. But, given fainting’s protective power, perhaps it’s time to revise this derogatory and uninformed view of syncope.

Fight, flight, or faint. Fainting is the body’s way of flipping a circuit breaker. It halts the action and perhaps even a pursuer. It can defuse conflict. It can enable escape. Fainting and its related spectrum of “slowing down” behaviors remain with us because over hundreds of millions of years they have helped animals evade death. Embedded in fainting’s ancient physiology is an important lesson for how we respond to the things that scare us. Fighting or fleeing your enemy may work some of the time. But when fighting is futile and fleeing not an option, just being still may offer an even more powerful form of protection.

Teens at the ear-piercing salon, fawns hidden in leaves, blood donors, and fish escaping predators have all inherited fainting’s death-evading neurocircuitry. Their conversing hearts and minds have bestowed upon them a respite—a momentary, deceitful reprieve that for eons has sometimes meant a way out.