The New Yorker, April 2011

Edited by Andy Ross

David Eagleman, 39, is an assistant professor of neuroscience at Baylor College of Medicine, in Houston. He has spent the past decade tracing the neural and psychological circuitry of the brain's biological clocks.

Brain time, as Eagleman calls it, is intrinsically subjective. How much of what we perceive exists outside of us and how much is a product of our minds? Time is a dimension like any other, yet the data rarely matches our reality. The jittery camera shake of everyday vision is smoothed over and our memories are often radically revised.

A few years ago, Eagleman ran an experiment to investigate the slowing down of perceived time under stress. First, Eagleman and a graduate student developed a perceptual chronometer. The unit could be strapped to a subject's wrist, where it would flash a number at a rate just beyond the threshold of perception. If time slowed down, Eagleman reasoned, the number would become visible. Then his team built SCAD, a "suspended catch air device." At the top of a tower, a subject would be hooked to a cable and lowered through a hole in the floor. His back would be to the ground, his eyes looking straight up. When the cable was released, he would plummet 110 feet, in free fall, until a net caught him near the ground.

A sense of time is threaded through everything we perceive. In Eagleman's 2009 essay "Brain Time," he writes that the brain is like Kublai Khan, enthroned in its skull, "encased in darkness and silence," at a lofty remove from brute reality. Messengers stream in from every corner of the sensory kingdom, bringing word of distant sights, sounds, and smells. Their reports arrive at different rates, often long out of date, yet the details are all stitched together into a seamless chronology. Kublai Khan was piecing together the past. The brain is describing the present.

Eagleman's mother was a biology teacher, his father a psychiatrist. As an undergraduate at Rice, Eagleman wanted to be a writer, but his parents persuaded him to major in electrical engineering. An extended sabbatical ensued. After his sophomore year, Eagleman joined the Israeli Army as a volunteer, then spent a semester at Oxford studying political science and literature, and finally moved to Los Angeles to become a screenwriter and a standup comic.

Back at Rice, he began to read books about the brain in his spare time and decided to take a course in neurolinguistics. For his doctoral work at Baylor, he programmed a piece of virtual neural tissue so complex that it tied up the Texas Medical Center’s new supercomputer for days. Eagleman's program showed that brain cells can exchange information not just through neurotransmitters but through the ebb and flow of calcium atoms. He went on to earn a postdoc at the Salk Institute, near San Diego. There he fell under the spell of Francis Crick.

Like Crick, Eagleman was fascinated by consciousness. He thought of time as a window on the movements of the mind. In a 2000 paper, Eagleman looked at the flash-lag effect. His version of the illusion consisted of a white dot flashing on a screen as a green circle passed over it. To determine where the dot hit the circle, Eagleman found, his subjects' minds had to travel back and forth in time. They saw the dot flash, then watched the circle move and calculated its trajectory, then went back and placed the dot on the circle. It was not prediction but postdiction.

If signals reach the brain within 100 ms of one another, any differences in processing are erased. The margin of error is surprisingly wide. Decades ago, Benjamin Libet, at the University of California, San Francisco, tested this by stimulating the cortical neurons of patients with electrical pulses. The subjects felt a tingle in the body parts wired to the neurons, but the stimulus didn't register for up to half a second.

Eagleman says that, like Kublai Khan,the brain needs time to get its story straight. It gathers up all the evidence of our senses, and only then reveals it to us. Perception and reality are often a little out of register. If all our senses are slightly delayed, we have no context by which to measure a given lag. Reality is carefully censored before it reaches us.

Eagleman ran the first round of SCAD experiments in 2007, with twenty subjects. He programmed the perceptual chronometer to flash its numbers just a little too fast to be legible. Then he stationed one observer at the top of the tower, to make sure the riders looked at the chronometer as they fell, and another on the ground. Afterward, the riders would report their chronometer readings, then take a stopwatch and go back over the experience in their minds, timing it from start to finish. Eagleman knew how long the fall took in real time and wanted to know how long it felt. On average, the subjects overestimate the length of their fall by 36 percent. But no matter how hard they stare at the chronometer, they can't read the numbers.

When something threatens your life, the amygdala seems to kick into overdrive, recording every last detail of the experience. The more detailed the memory, the longer the moment seems to last. "Time is this rubbery thing," Eagleman said. "It stretches out when you really turn your brain resources on, and when you say, 'Oh, I got this, everything is as expected,' it shrinks up."

Early this winter, Eagleman was in London for a study of time perception in drummers. The idea of studying drummers had come from Brian Eno, the composer, record producer, and former member of the band Roxy Music. Eno first met Eagleman two years ago, after a publisher he knew sent him a book of Eagleman's short stories, called Sum.

Sum has forty chapters, each describing a different version of the afterlife. Eagleman establishes a set of initial conditions, then lets the implications unfold logically. Sum took years to find a publisher. In England, reviewer Geoff Dyer called it "stunningly original" and saw in it "the unaccountable, jaw-dropping quality of genius." Scientists and religious readers alike praised it.

Eno suggested a staged reading of the book. The production premièred at the Sydney Opera House in June 2009, with a score by Eno. There Eno told Eagleman the story that inspired the drumming study. Eagleman arrived at Eno's studio the next day carrying a pair of laptops and a wireless EEG monitor. He clamped the EEG on his head and watched as sixteen wavering lines represented the electrical activity at points in his brain. The drummers would wear this while taking a set of four tests.

Eno was right: drummers have more exact time perception than most people. Eagleman planned to use the EEG data to locate the most active areas of the drummers' brains, then target them with bursts of magnetic stimulation to see if he could disrupt their timing.

In May, Pantheon publishes Eagleman's popular account of the unconscious, Incognito.

AR  I guess this is a man to take seriously. Like him, I think our perception of time is crucial to understanding how the brain supports our consciousness.