By MARGARET WERTHEIM N.Y. Times News Service
SAN DIEGO - Sitting at lunch on the patio of his home here one muggy day last June, Francis Crick was expounding on the mind-body problem and the thorny subject of the human “self.”
Where is the line between mind and matter? he asked. Besides the neurons in our brains, the human body contains tens of millions of neurons in the enteric nervous system, which extends into the stomach and intestines. “When you digest your lunch is that you?” Crick asked.
Body and mind are the twin problems around which Crick’s life has spiraled, much like the double helix structure of DNA that he and Dr. James D. Watson are famous for discovering half a century ago. Though his research on “the molecule of life” is what he is best known for, in his 28 years at the Salk Institute for Biological Studies, his work has focused on the mind, and, in particular, the question of consciousness.
Until recently, that subject was viewed with deep suspicion in scientific circles, but Crick has led a campaign to make it acceptable. These days it is even fashionable. While some philosophers claim that consciousness is a phenomenon outside the purview of material science, Crick dismisses such arguments with the imperious confidence that is part of his legend. “The mechanism is the important part; the rest is just playing with words,” he said in a recent interview.
Crick’s career has been characterized by celebrated collaborations, and for the past decade he has been working with Dr. Christof Koch, a professor of computation and neural systems at the California Institute of Technology. Together they have developed a framework, which Koch has spelled out in his new book, The Quest for Consciousness: A Neurobiological Approach.
In late March, Crick and Koch sat down in San Diego to discuss their recent work. Now 87 and suffering from the advanced stages of cancer, Crick has been put on a new regime of chemotherapy. Yet despite the toxic cocktail, he seems as sharp as ever, tossing out answers like perfectly aimed darts.
Almost from the start of his career, he was obsessed with two problems: “the borderline between the living and the nonliving and the nature of consciousness.” In the late 1940s, after a notable career as a physicist in the British Admiralty, he began to investigate the first topic by studying the structure of proteins.
In 1951 he teamed up with Watson to determine the structure of DNA. Few scientists believed DNA carried the genetic code, but then-Mr. Crick -- he did not get his doctorate until 1954 -- and Dr. Watson were convinced that it did. Their epoch-making paper on the double helix was published in 1953, and in 1962 they won the Nobel Prize in Physiology or Medicine, with their colleague Dr. Maurice Wilkins.
Crick next collaborated with Dr. Sydney Brenner, and together they worked on the problem of how the genetic code translated into proteins that build organisms. By the end of the ’60s, the foundations of molecular biology were well understood, and Crick was eager to go to his next great question. In 1976 he moved to the Salk Institute, reinventing himself as a neuroscientist.
Since then, Crick has been a tireless champion of the brain. In a 1979 editorial in Scientific American, he argued that the time had come for science to take on the previously forbidden subject of consciousness. In his 1994 book The Astonishing Hypothesis: The Scientific Search for the Soul, he went further. “You,” he wrote, “your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will are, in fact, no more than the behavior of a vast assembly of nerve cells and their associated molecules.” He outlined an empirical approach focusing on visual consciousness.
His ideas have formed the inspiration for Koch’s research at Caltech: the goal is to find “the neural correlates of consciousness,” or NCCs -- the neuronal states and processes associated with conscious awareness.
Koch and his graduate students are finally gaining experimental evidence for what Crick had termed the “awareness neurons” that enable us to see.
Crick’s ideas, along with those of another Nobelist, Dr. Gerald M. Edelman, helped shift the direction of neuroscience. These days, papers on the neural correlates of consciousness are increasingly commonplace, though Dr. Nancy Kanwisher, a neuroscientist at the Massachusetts Institute of Technology, noted that still “very few neuroscientists directly discuss the NCCs.”
But even Dr. David Chalmers, a philosopher at the University of Arizona and a leading critic of the materialist approach to mind, acknowledges the value of the work of Crick and Koch. “Everyone agrees now that there are systematic processes happening in the brain that must correlate with awareness,” he said.
Many of Koch’s experiments are aimed at teasing out what the brain is registering beneath the radar of conscious awareness. One tool for studying this is trace conditioning. Using it, a subject is presented with two consecutive stimuli -- say an image and a mild electric shock -- separated by a delay. After a period of training, subjects begin to anticipate the shock (measured by a rise in skin conductance on their palms) when they see the image.
Using MRI, Koch’s team has shown that in trace conditioning, an area of the brain known as the anterior cingulate cortex is activated. They have found that when they remove this area from mice, the creatures cannot be trace conditioned, causing Koch to speculate that this area of the brain is critical for consciousness.
Koch notes that the advent of MRI has also made it possible to see which parts of the brain are active during a “percept” -- as when someone sees a face. Kanwisher has shown that there are specific parts of the brain that register awareness of faces and objects.
A small group of patients with epilepsy are letting scientists get an even more intimate look at the brain. Working with Dr. Itzhak Fried, a neurosurgeon at the University of California, Los Angeles, graduate students of Koch’s are exposing the patients to images and checking the activity of individual neurons as recorded by electrodes implanted in their brains.
Koch’s team is looking for neuronal evidence of “change blindness” in these patients. An array of four photographs is flashed on a screen, followed about a second later by another array in which one of the images has changed. “It can be surprisingly difficult to consciously see such changes,” Koch said, though evidence suggests that neurons may be registering them.
Not everyone is convinced that understanding the neural correlates will explain awareness. “There is a difference between correlation and explanation,” Chalmers said. “The question is, once we have these neural correlates, what do we do with them? I don’t think the NCCs is a final theory.”
In tackling consciousness, Crick and Koch have reframed the central question. Traditionally the problem has been cast in terms of subjectivity. How is it, for example, that when someone sees red (which physically speaking is electromagnetic waves of a particular frequency) there is also a subjective feeling of redness?
The “redness” of red and the “painfulness” of pain are what philosophers refer to as qualia. The gap between the objectivity of material science (the electromagnetic waves) and the subjectivity of human experience (the qualia) has led some philosophers to conclude that this chasm cannot be bridged by any materialist explanation.
Rather than getting bogged down in the depthless ooze of qualia, Crick and Koch sidestep the issue. Instead of asking the philosophical question of what consciousness is, they have restricted themselves to trying to understand what is going on at the neurological level when consciousness is present.
While many scientists assume that consciousness is a global property of the brain -- “a gestalt phenomenon” -- Koch and Crick say they believe that only a few neurons are responsible at any given moment. Of the 50 billion or so neurons in the brain, Crick says that perhaps only tens of thousands, or even a few thousand, give rise to the feeling of conscious awareness. “We believe it is essentially a local phenomenon,” he said.
That position is certainly contentious. “The idea that there is a special population of neurons that mediate awareness is a minority view,” Kanwisher noted.
Crick says he is convinced that the origin of consciousness is a solvable problem, albeit complex.
He drew an analogy with another phenomenon once attributed to transcendent powers: “People think the brain is mysterious but not the weather. Why is that?” In some ways, he suggested, the brain may be less enigmatic than the weather, because “we don’t yet have a clear understanding of how raindrops form but we do know how individual neurons and synapses work.”
The elucidation of the double helix ushered in the age of molecular genetics, which has now given rise to the vast applications of genetic engineering. Elucidating consciousness could have similarly portentous results, Koch suggests.
One potential application, he says, is some kind of instrument for measuring its intensity, perhaps a “consciousometer.” Anesthesiologists might use it to determine when a patient under sedation is truly out. But in his book, Koch also raises the possibility of more troubling uses, including measuring the awareness levels of severely retarded children and elderly patients with dementia.
Or, he asks, “How do we know that a newborn baby is conscious?” Perhaps consciousness is something that doesn’t begin at birth, he said, but gradually emerges.
“This research is going to pose enormous legal and ethical questions,” Koch acknowledged in the recent interview.
“I’m not convinced that people want to know how consciousness works,” he said. “They feel cast out of the world of meaning.”
Having solved one of the basic mysteries of life here on Earth, Crick seems happy to skewer any notions of a life beyond. For him, the most profound implication of an operational understanding of consciousness is that “it will lead to the death of the soul.”
“The view of ourselves as ‘persons’ is just as erroneous as the view that the Sun goes around the Earth,” he said. He predicted that “this sort of language will disappear in a few hundred years.”
“In the fullness of time,” he continued, “educated people will believe there is no soul independent of the body, and hence no life after death.”