This Is Your Brain on Anesthesia
YOU MIGHT BE OUT FOR THE COUNT, BUT SCIENTISTS CAN STILL LEARN A LOT FROM THE ANESTHETIZED BRAIN.
UNTIL THE middle of the 19th century, surgery was performed with no anesthesia. You don’t need a fertile imagination to realize how excruciating the experience was for patients. Nor did the surgeons who administered this particular type of torment take it lightly.
In e Worst of Evils: e Fight Against Pain, scientist and author omas Dormandy describes how 19thcentury surgeon and medical pioneer Sir James Paget recalled those gruesome days before anesthesia in his memoirs: “ ey had been the worst nightmares. I can remember them still. Even now, they sometimes rouse me from my sleep. I wake drenched in sweat.” Paget wasn’t the only one who was disturbed by the experience. Charles Darwin dropped out of medical school at least partly because he didn’t have the stomach for pre-anesthesia surgery.
ese days, surgery is much less traumatic: You start counting backward from 100, and before you get to 95, you nd yourself waking up in recovery. Modern anesthesia is genuinely one of the miracles of modern medicine. While the surgical team takes care of business, you’re checked out. But what happens to your brain during the time you aren’t there?
ANESTHESIA doesn’t shut down the brain. Instead, it interferes with the communication of neurons across different parts of the brain. e ability to experience anything, from thinking to processing sensory experiences — such as what it feels like to have your body sliced open and your innards tinkered with — depends on this more or less constant neuronal chatter.
Some scientists have found that anesthesia dramatically alters this chatter. e result? “Essentially, a drug-induced coma,” explains Miles Berger, an anesthesiologist and neuroscientist at the Duke University Institute for Brain Sciences.
He compares it to an old television
that goes from a normal picture to rolling static waves. “ ere may actually be more total signal in the case of the static waves,” he says, “but the information transfer is less.” e neurons are still active under anesthesia, but it’s as if all the information is lost and replaced by those large static waves.
Being anesthetized is very di erent from being asleep, but in both cases, the brain is active, even if we’re unaware of it. Using electroencephalography (EEG) to track electrical activity in di erent parts of the brain while we’re anesthetized can help neuroscientists better understand our minds — and even potentially screen for brain illnesses. Berger and colleagues have found that EEG patterns from patients under anesthesia may help identify those most likely to have delirium post-surgery, a common problem in older patients.
In addition, studying how brains respond to anesthesia might one day help to screen patients for cognitive decline. Berger uses the analogy of a stress test for heart disease. Cardiologists put people on treadmills to see how their hearts respond to exercise stress. at can help determine how likely a patient is to have a heart attack. Berger and his colleagues see anesthesia and surgery as something similar — a stressor for the brain.
“If we can monitor the brain in real-time and see how it’s responding to the stress of surgery and anesthetic drugs,” he says, “that could allow us to predict who might potentially have a brain problem in the future.” is wouldn’t diagnose dementia or even early cognitive decline, but it might one day be a useful screening tool.
“Our hope,” says Berger, “is that we can identify people who are at risk for cognitive decline just by looking at how their brains respond to anesthesia, and then those patients can be referred for further workup.”
COMING TO terms with death isn’t easy — even if you’re an insect that’s little more than an eighth of an inch in size.
For fruit ies, or Drosophila melanogaster, the mere sight of their companion’s corpses can trigger certain cues known to alter their brain chemistry, deplete fat stores, and even cause other ies to avoid them, as if the traumatized insects still carried the stench of death.
What’s more, scientists from the University of Michigan have found that fruit ies who witness their dead comrades age faster and die sooner. ey’ve peered inside the insects’ pintsized brains to better understand what happens when fruit ies are exposed to death, according to a 2023 study in PLOS Biology. e research may have implications for pausing the clock on human aging triggered by trauma, as well.
ACROSS THE ANIMAL kingdom, a number of species are aware of death’s looming specter, each reacting in their own unique way.
Social insects like ants and honeybees, for example, act as impromptu undertakers, carting dead colony members away from the nest. e behavior — known as necrophoresis — is, in part, triggered when the deceased insects no longer emit life-a rming chemical compounds, which their living companions can sense.
Other examples abound, too. When female baboons grieve a dead relative, they’re ooded with increased stress hormones, much like humans. Elephants, meanwhile, will mourn openly, including standing guard over the bodies of the deceased, touching
the corpse with their trunk and even making noises.
“Apes are close to us, so you’d expect [that type of behavior],” says Christi Gendron, a neurobiologist at the University of Michigan and co-author on the new study. “But, speci cally, the way that elephants mourn their dead and show altered behaviors has always been one of the most striking [to me].”
Since these responses share similarities across species, researchers like Gendron suggest that the physiological processes behind them might be shared, too, including among humans.
GENDRON AND study co-author Tuhin S. Chakraborty found out how living fruit ies respond to the sight of dead ones almost by accident. “[Chakraborty] stumbled upon it,” says Gendron. “ e initial question that he was asking was whether ies can sense other sick ies. You hear stories of dogs that can sense sickness in humans, and we were trying to understand the neurobiology there.”
To study that, Chakraborty infected fruit ies with a bacterial pathogen. When those ies died, healthy ies housed with the cadavers began losing stored fat, sent out a signal to other ies to stay away and died more quickly than their counterparts. e scientists published those results in 2019.
For the latest experiment, the team wanted to better understand how the neural circuitry in living ies was translating the sensory perception of death into a diminished life span. ey were able to track the ies’ brain activity by tagging them with a uorescent green protein that enabled the scientists to see when — and where — the insects’ neurons had been activated. Dissecting those corpse-exposed ies showed heightened activity in the ellipsoid body, a part of the brain responsible for processing sensory information.
e scientists then identi ed the speci c population of neurons necessary for that activity in the sensory region of the brain. Later, when those same neuron clusters were stimulated, the ies died sooner, even if they had never been exposed to a dead y before.
Unfortunately, humans must confront death, too. And for those who are routinely exposed to stressful situations that surround death, like military personnel and rst responders, the consequences can threaten their longevity, as well. “[ ose individuals] o en su er cardiovascular issues,” says Gendron. “ ey also su er psychological issues, potentially, like PTSD and depressive disorders.”
By understanding the pathways responsible for processing death, even in a basic organism, the researchers hope to pave the way towards therapies, including drugs, for treating those individuals — and, in turn, potentially extending their lifespan.
Dissecting those corpse-exposed flies showed heightened activity in a part of the brain responsible for processing sensory info.