Measuring consciousness

In a feature article for the Atlantic, Joshua Lang explores the phenomenon of anesthesia awareness: where patients undergoing surgery are conscious yet paralyzed and thus unable to signal the pain and terror they are experiencing.

On a warm afternoon in Madison, Wisconsin, last spring, a psychiatrist was pointing an electromagnetic gun at my brain.

“Put your arm in your lap,” he said.

I obeyed. My head was dressed in a 60-electrode, high-density EEG-recording device. The doctor stood behind my chair, eyeing a digitized MRI of my brain and gliding the gun over my scalp until he found his target: my motor cortex.


I tried.

The gun clicked. My forehead muscles twitched. My arm leapt out of my lap, straight into the air, as if yanked by invisible puppet strings. “Do it again,” I said.

This process is called transcranial magnet stimulation, or TMS. It is the key to a device that Giulio Tononi, one of the most-talked-about figures in anesthesiology since Nassib Chamoun, hopes will provide a truly comprehensive assessment of consciousness. If successful, Tononi’s device could reliably prevent anesthesia awareness. But his ambitions are much grander than that. Tononi is unraveling the mystery of consciousness: how it works, how to measure it, how to control it, and, possibly, how to create it.

At the heart of Tononi’s work is his integrated-information theory, which is based on two distinct principles, as intuitive as they are scientific. First, consciousness is informative. Every waking moment of your life provides a nearly infinite reservoir of possible experiences, each one different from the next. Second, consciousness is integrated: you can’t process this information in parts. When you see a red ball, you can’t experience the color red separately from the shape of the ball. When you hear a word, you can’t experience the sound of it separately from its meaning. According to this theory, a more conscious brain is both more informative (it has a deeper reservoir of experiences and stimuli) and more integrated (its perception of these experiences is more unified) than a less conscious one.

Compare the brain to New York City: just as cars navigate the city’s neighborhoods via a patchwork of streets, bridges, tunnels, and highways, electrical signals traverse the brain via a meshwork of neurons. Tononi’s theory predicts that in a fully conscious brain, traffic in one neighborhood will affect traffic in other neighborhoods, but that as consciousness fades—for instance, during sleep or anesthesia—this ripple effect will decrease or disappear.

In 2008, in one of several experiments demonstrating this effect, Tononi pulsed the brains of 10 fully conscious subjects with his electromagnetic gun—the equivalent of, say, injecting a flood of new cars into SoHo. The traffic (the electromagnetic waves) rippled across Manhattan (the brain): things jammed up in Tribeca and Greenwich Village, even in Chelsea. Tononi’s EEG electrodes captured ripples and reverberations that were different for every subject and for every region of the brain, patterns as complex and varied as the traffic in Manhattan on any given day.

Tononi then put the same subjects under anesthesia. Before he pulsed his gun again, the subjects’ brain traffic seemed as busy as when they were conscious: cars still circulated in SoHo and Tribeca, in Greenwich Village and Chelsea. But the pulse had a drastically different effect: This time, the traffic jam was confined to SoHo. No more ripples. “It’s as if [the brain] has fragmented into pieces,” Tononi told me. He published these findings in 2010, and also used them to file a patent for “a method for assessing anesthetization.”

It seems emblematic of the contemporary bio-medical approach to understanding human experience, that in attempting to understand the nature of consciousness one of the most valuable outcomes might be a method for verifying unconsciousness.

Print Friendly, PDF & Email