The paperback version of Incognito: The Secret Lives of the Brain is out. In celebration, NPR’s Fresh Air broadcast its wide-ranging interview with neuroscientist David Eagleman again yesterday. But this was the first time I heard it. Definitely enjoyed it – time perception, metaphors for how the brain works, neuroscience and law, responsibility and mental health courts, his own personal motivations for his research, neural diversity, science and fiction, and more.
The interview does come across as a bit simplistic at times – the brain as composed of a team of rivals – yet that also helps people cross the neuroscience bridge to popular understanding. The reader comments on Amazon reflect this – a neuroscientist skewers it, Book Fan finds it a fascinating tour. Similarly, while I had some reservations, my wife really liked the interview. Overall, this is neuroscience that is active in the public sphere, and that I do applaud.
For both of us, the Ulysses metaphor – lashing himself to the mast to hear the song of the siren, and thus setting up a contract with his future self (with the boat as a metaphor for the rest of his brain) – worked well. It provides a way for readers to understand themselves, to develop a perspective on how their brain works. It is not, however, a fundamental treatise on neuroscience. Eagleman, as he says, is fundamentally interested in consciousness and how we perceive the world. Including our own brains!
“Time is an active construction of the brain,” Eagleman says to Terry Gross. A New Yorker profile of Eagleman outlines this research more; Eagleman also writes about this topic in the Edge essay, Brain Time. In the NPR interview, here is how Eagleman describes his research on time perception during extreme moments:
GROSS: You’re dropped 150 feet, and then you land on a net, which hopefully catches you safely, without any damage. But you ask people to do that – who were doing that jump, to give you a sense of how long they thought the fall was, and then you would…
EAGLEMAN: That’s right.
GROSS: Then you would actually measure how long it actually was. What did you find?
EAGLEMAN: Well, actually we had them retrospectively estimate how long they thought the fall was. But the key part of the experiment is we developed a device that we strapped to people’s wrist that flashes information at them in a particular way while they’re falling. So we could actually measure time perception as they’re in freefall.
And it’s very scary, this fall, because you’re falling backwards, and you’re going very fast when you hit the net, and it takes about three seconds.
And what we find is that people think it takes a long time. When you’re actually doing the fall, it feels like it takes a very long time, and yet what we found is that during the fall, people are not able to actually see in slow motion, like Neo in “The Matrix.”
So what this means is – what we found from this is that time and memory and deeply intertwined, and so when you’re estimating how long something lasted, when you say, whoa, that felt like it took forever, what that really has to do with, at least as far as we can tell right now, is the laying down of very dense memories during a scary situation.
So when something is really hitting the fan, that’s when your brain is completely focused on the situation and writing down everything, and when you read that back out, it seems like it must have taken forever because we’re not used to being in the zone like that. We’re not used to noting every detail and remembering everything. And so we – our estimates of time are often influenced by memory.
As he continues in the NPR interview, “Time is not one thing to the brain. It’s not like a piece of footage that you stretch or squish. Instead, you have different parts of the brain that care about duration, those that care about temporal order, those that care about flicker rate, those that care about auditory pitch and so on. Normally, these work in concert, and we think that time is just one thing. But what we’ve been doing in the laboratory is teasing these apart and showing that time is really a construction of the brain.”
This “specialization yet mostly working in concert” phenomenon is part of how Eagleman approaches “Secret Lives of the Brain.” But his “brain as competing factions” metaphor goes beyond that, to posit that different neuronal groups can basically have conflicting opinions on the same thing. Here is an excerpt from a Baylor news article describing Eagleman’s work on visual illusions.
Illusions in Perceived Motion
Eagleman and two of his students, Giovanni Piantoni and Keith Kline, asked participants to watch a series of dots moving in one direction. Occasionally, participants suddenly reported the illusory perception that the dots moved in the other direction. Using electroencephalography (EEG), a method used to record the activity of large groups of neurons, the researchers were able to measure the difference in brain activity during correct and illusory perception.
“It’s a powerful approach: nothing about the display is changing, and yet your perception of what you’re seeing occasionally reverses entirely,” Eagleman said. “This allows us to ignore the low-level mechanics of the visual system and instead measure the neural activity that underpins the content of visual awareness.”
Neural Coalitions Compete
The researchers found that they could detect the activity of one coalition of neurons break down — and another coalition build up — whenever the perception of motion switched. These changes in the neural activity correlated with what participants reported seeing.
This provided direct evidence that the neural populations underlying the two possible perceptions compete with one another for dominance, and whichever one wins determines the content of consciousness, Eagleman said.
“Think of the two populations of neurons as political parties, each fighting for control of the senate,” said Eagleman. “When one party gets its strategies aligned, it can topple the other and take control for a short time.”
What causes both coalitions to be activated even though the motion is only in one direction? Earlier research from Eagleman’s laboratory suggests that continuous motion has a small effect of “tickling” motion detectors that represent the opposite direction. This allows the opposite direction to enter the fray.
“Even though an observer is presented with leftward motion and most of her visual system gets that correct, a small population of neurons will insist that the motion is in the other direction. That is when the rivalry starts, each coalition fighting the other for power,” Eagleman said. “The larger coalition wins most of the time, but occasionally there is a brief, surprise overturn.”
For more, you can see the Eagleman and Raymond Tallis (critic of “neuro-mania”) debate “who’s in charge” earlier this year. Neither gets beyond the brain-culture divide, Tallis insisting on the power of culture, Eagleman on unconscious brains, so it definitely illustrates the arenas where neuroanthropology stakes its ground.
And for that ground, interesting neuroscience research is needed. Eagleman runs the Laboratory for Perception and Action at Baylor. You can get the list of his publications, and find out more about his lab’s work on time perception, synesthesia, neuroscience and the law.
Incognito: Laboratory for Perception and Action
Mind & Brain illustration: Lapidarium Notes (with more on Eagleman’s view on how we neuro-construct reality)
David Eagleman: Wikipedia entry on Eagleman
Paperback Incognito: The Secret Lives of the Brain on Amazon