Inside the search for a universal signature of the unconscious

Imagine a calm, flat ocean dotted with countless buoys. A few of them begin to sway, the glassy water rippling. Suddenly, groups of buoys begin jumping and splashing again in unison, sending up waves. Others join. Then more. The ocean becomes a torrent of undulating hills. Is there some kind of pattern?

I noticed that the waves affect the frenetic activity of the buoys. The waves created by the buoys seem to move with purpose, an apparently coordinated spectacle. But this is not a chaotic ocean storm. What you are watching is an improvisational and wise dance.

Now, imagine that the ocean is your brain. Floaters are neurons. Waves are electrical activity. And their mysterious, patterned movements? This is awareness.

To better understand consciousness, neuroscience has traditionally focused on neurons, which are the primary carrier of information in the brain. But neuroscientists like Earl K. Miller argues that coordinated brain waves do the real work—carrying, integrating, and transforming information—and perhaps even creating consciousness.

Miller’s latest research explores this idea in a counter-intuitive way — by studying how different anesthetics chemically alter brain wave patterns in similar ways, leading to the same vanishing point: loss of consciousness. The hope is that observing how consciousness falls apart may reveal what holds it together.

Global signature

One of the great mysteries of science is why we experience the world subjectively. It’s a big, controversial, and intellectually engaging question. But not what interests miller, Picower Professor of Neuroscience at MIT and a member of the Picower Institute for Learning and Memory. “This is something philosophers should take into account,” he says. “I’m interested in how the brain produces consciousness – the underlying mechanisms and principles.”

To study those, Miller W Members of his laboratory Regularly investigate loss of consciousness. Examining the unconscious enables researchers to explore the factors in the brain that allow consciousness to emerge in the first place. “You’ve shut the whole thing down, and now you can ask what changed in the brain,” says Daniel Tucker, a neuroscientist at UCLA who also researches consciousness via the unconscious.

The most reliable way to do this is through anesthesia. Inhalable medications such as sevoflurane, desflurane, and isoflurane — along with stronger injectable medications such as propofol, ketamine, and dexmedetomidine — disrupt brain activity to the point where the organ loses its ability to process and integrate information. Your personal experience becomes black.

Surprisingly, scientists have only recently learned how anesthesia leads to loss of consciousness. In a He studies Last year, Miller and his colleagues detailed how the pioneering drug propofol causes the disappearance of consciousness. “The brain has to operate on a knife’s edge between arousal and chaos,” Miller said He explained. “It needs to be excitable enough for its neurons to influence each other, but if it becomes too excitable, it spirals into chaos. Propofol appears to disrupt the mechanisms that keep the brain in this narrow operating range.”

Generalized seizures also cause the brain to lose consciousness, but in a different way than anesthesia. “When you’re drugged, you get into this chaotic, unstable system,” Tucker says. “Whereas in generalized seizures, the brain becomes a super-predictable metronome.”

Miller and his team have had much greater success in verifying loss of consciousness through anesthesia. In a He studies Published in May, he and Alexandra Bardon, a graduate student, administered two different anesthetics, ketamine and dexmedetomidine, to macaques while recording the animals’ brain activity. With both drugs, the alignment of brain waves changed in similar ways when the animals’ consciousness dimmed and then blinked.

This easily measurable shift may be a universal sign of the unconscious: a neural pattern that sends reliable signals when consciousness disappears, regardless of the reason. “Our study suggests that anesthetics all cause loss of consciousness in the same way,” Miller says. “They may get there in different ways, but they change your brain waves in very specific ways.”

Riding a (brain) wave.

The findings deepen Miller’s long-standing metaphor of the brain as an ocean — waves of electrical activity rising and interacting across the cerebral cortex. It is thought that these waves may do more than simply reflect the firing of nerve signals. They may help bind consciousness together.

While the major theories of consciousness differ in many ways, most agree that consciousness arises when enough of the cerebral cortex — the outer layer responsible for high-level functions like thinking and memory — are buzzing in coordinated harmony. “Brainwaves are a great way to do this,” Miller says, “because how do you coordinate millions of neurons across your cerebral cortex?”

Waves offers an elegant solution to this problem. As simple functions, they provide an effective way to coordinate and regulate patterns of activity across the brain. “It’s a great, easy way for the brain to produce self-regulation,” Miller says.

For much of the 20th century, neuroscientists believed that neurons did the heavy lifting of producing conscious experience through a process called spiking, which involves sending a signal via an electrical pulse known as an action potential. Most neuroscientists considered it vague to suggest that brain waves could be the drivers of consciousness. After all, it wasn’t clear whether brain wave patterns were merely useful biomarkers, or whether their changes could reveal something deeper about consciousness itself. “Does consciousness disappear because brain waves change in this way, or is this just a weird reading that means nothing functionally?” Tucker says.

But recent research has reignited interest in brain waves. In 2012, a research team led by Miller at MIT, along with a group from Boston University, Interconnected Brain wave activity with different thoughts in the brains of monkeys. Six years later, scientists at Yale University found it Show At the precise moment of conscious perception of stimuli, a wave of electrical activity flows from the visual cortex at the back of the brain to the frontal lobes.

The result: Scientists have realized that stimulating neurons is not the only thing responsible for consciousness. In fact, researchers have discovered that neurons spend about 80% of their time not spiking. During these periods, they continue to communicate with other brain cells through subtle electrical influences. These effects – waves – travel around the brain 5,000 times faster than the slower signal of synaptic spikes, and they are sent all the time.

Scientists have also discovered that astrocytes — the star-shaped glial cells that make up up to 40% of all cells in the brain — do more than just structurally support neurons, remove waste, and provide nutrients. Like neurons, they also oscillate and spread electrical influences. In May, a team led by Thomas Babwin, an assistant professor of neuroscience at Washington University in St. Louis, found that a brain chemical linked to alertness, attention, and learning changes brain connectivity and function by acting on astrocytes, not neurons. As he said in A statement“This is the kind of discovery that reshapes our deep understanding of how the brain works.”

Your brain is not a MacBook

For decades, neuroscientists have assumed that the brain operates like a digital computer, a living, breathing MacBook Pro. Neuronal spikes were viewed as ones and zeros, and were considered carriers of information.

But Miller embraces another hypothesis that fits with the idea that brain waves, not neurons, drive consciousness: the mind actually works like an analog computer. These machines solve problems by representing quantities as models—think mechanical voltages or positions—rather than the ones and zeros used in digital computers.

In an analog brain, waves can easily serve as those models, Miller says. Calculations can arise from how waves interact, add up or cancel out depending on their phases. Because these waves ripple through the brain’s three-dimensional structure, they can support very complex calculations. (Unlike digital zeros, waves can take all values ​​in between.)

Miller points to the tiny power usage of the human brain—just 20 watts—as evidence that his computational approach should be vastly more efficient than today’s power-hungry digital supercomputers. Although their needs reach tens of megawatts, supercomputers still cannot match the raw computing power of the human brain.

“Biology solves problems in an energy-efficient way,” Miller says. “In addition, your brain is constantly creating the raw materials for (analog computing) – these oscillating waves that travel in your cerebral cortex. If evolution doesn’t exploit that – this clear, powerful, highly efficient solution – (then) I don’t understand evolution.”

Automated anesthesia

For Miller, understanding the basic mechanism of consciousness through anesthesia is not just an abstract scientific goal. It’s one that has real-world benefits. Along with his MIT colleague and practicing anesthesiologist Emery N. BrownHe hopes to bring them into mainstream clinical practice.

In most operating rooms today, anesthesiologists monitor a patient’s heart rate, blood pressure, and physical movements to make sure they do not feel pain or regain consciousness. They rarely track brain activity using electroencephalograms (EEGs). Miller and Brown argue that EEG should become a standard tool because it provides a more direct and reliable window into the actual brain state under anesthesia. “It makes perfect sense to me that you would be observing the thing that is unconscious, which is the brain,” Miller says. “But to do that, you have to know what the neural signatures of consciousness are.”

Based on his recent study of macaques, Miller’s goal is to definitively identify the brain wave signature of loss of consciousness in humans. By knowing this key sign, anesthesiologists can provide patients with the necessary amount of medication to reach unconsciousness and nothing more. Miller and his team have already built a prototype of a machine that automates anesthesia administration and works extremely well in animal models.

What is the benefit of this type of machine? On the one hand, it can significantly reduce the number of patients who regain consciousness during major surgeries. It is estimated that it is approx One or two out of every 1,000 surgeries Under general anesthesia, the patient regains consciousness. They probably won’t feel any pain, but the experience can be uncomfortable.

More importantly, an automated anesthesia machine based on the brain wave signature of consciousness can prevent surgical patients from overindulging in anesthesia. Anesthetics are strong and can move Permanent harmful effectsespecially on the very young and the elderly. The lower the amount, the better. For those over 65, anesthesia can cause short-term symptoms and Long-term cognitive decline. Miller says anesthesia also worsens dementia, Alzheimer’s disease and almost every mental illness.

Tucker also emphasizes the real-life benefits of probing the subconscious. The ultimate goal of his research is to find ways to awaken people affected by disorders of consciousness. Many of these patients live in either a comatose or barely conscious state, where they are fully “awake” but unaware, or only minimally aware of their surroundings. As many as 300,000 Americans are imprisoned in these gray areas of consciousness, often hidden away from public view.

“Studying consciousness is interesting, but if we think: ‘What’s the point of doing this kind of research?’ “For me, it’s really about helping patients who can’t consciously perceive anything,” says Tucker. “If we can study what goes wrong in their brains, it will not only be useful for the general science of consciousness, but it may also help wake some people up.”