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Do Big New Brain Projects Make Sense When We Don't Even Know the "Neural Code"?

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Does anyone still remember "The Decade of the Brain"? Youngsters don't, but perhaps some of my fellow creaky, cranky science-lovers do. In 1990, the brash, fast-growing Society for Neuroscience convinced Congress to name the '90s the Decade of the Brain. The goal, as President George Bush put it, was to boost public awareness of and support for research on the "three-pound mass of interwoven nerve cells" that serves as "the seat of human intelligence, interpreter of senses and controller of movement."

One opponent of this public-relations stunt was Torsten Wiesel, who won a Nobel Prize in 1981 for work on the neural basis of vision. When I interviewed him in 1998 for my book The Undiscovered Mind, he grumbled that the Decade of the Brain was "foolish." Scientists "need at least a century, maybe even a millennium," to understand the brain, Wiesel said. "We are at the very beginning of brain science."

I recalled Wiesel's irritable comments as I read about big new neuroscience initiatives in the U.S. and Europe. In January, the European Union announced it would sink more than $1 billion over the next decade into the Human Brain Project, an attempt to construct a massive computer simulation of the brain. The project, according to The New York Times, involves more than 150 institutions. Meanwhile, President Barack Obama is reportedly planning to commit more than $3 billion to a similar project, called the Brain Activity Map.

Some scientists are criticizing these big initiatives in ways that remind me of Wiesel and the Decade of the Brain. The New York Times quoted brain researcher Haim Sompolinsky saying of the Human Brain Project, "The rhetoric is that in a decade they will be able to reverse-engineer the human brain in computers. This is a fantasy. Nothing will come close to it in a decade."

The U.S. mapping project, neurologist Donald Stein told The Times, is based on a view of the brain that "is, at best, out of date and at worst simply wrong. The search for a road map of stable neural pathways that can represent brain functions is futile."

Henry Markram of the Swiss Federal Institute of Technology, the leader of the Human Brain Project, has been bragging about his computer model, Blue Brain, for years. But as I pointed out three years ago, his computer simulations can't perform any cognitive functions, such as seeing, hearing, remembering, deciding, so there is no way of telling whether they are capturing essential features of brains.

I compared the models of Markram and others to those plastic brains that neuroscientists like to use as paperweights. Another analogy is the "planes" that Melanesian cargo-cult tribes built out of palm fronds, coral and coconut shells after being occupied by Japanese and American troops during World War II. "Brains" that can't think are like "planes" that can't fly.

In spite of all our sophisticated instruments and theories, our own brains are still in many respects as magical and mysterious to us as a cargo plane was to those Melanesians. Neuroscientists can't mimic brains because they lack basic understanding of how brains work; they don't know what to include in a simulation and what to leave out.

Proponents of the big brain projects are comparing them to the Human Genome Project. There are two problems with that analogy. First, the Genome Project was an impressive technical achievement, but since its completion 10 years ago it has failed to deliver any significant medical breakthroughs. [See Postscript.] Moreover, the Genome Project built upon a basic understanding of genetics. Decades before the Genome Project was launched, researchers deciphered the genetic code, the set of rules whereby specific sequences of base pairs in DNA generate specific proteins.

Neuroscientists have faith that the brain operates according to a "neural code," rules or algorithms that transform physiological neural processes into perceptions, memories, emotions, decisions and other components of cognition. So far, however, the neural code remains elusive, to put it mildly.

The neural code is often likened to the machine code that underpins the operating system of a digital computer. According to this analogy, neurons serve as switches, or transistors, absorbing and emitting electrochemical pulses, called action potentials or "spikes," which resemble the basic units of information in digital computers.

But the brain is radically unlike and more complex than any existing computer. A typical brain contains 100 billion cells, and each cell is linked via synapses to as many as 100,000 others. Synapses are awash in neurotransmitters, hormones, neural-growth factors and other chemicals that affect the transmission of signals, and synapses constantly form and dissolve, weaken and strengthen, in response to new experiences. Researchers have recently established that not only do old brain cells die, new ones can form via neurogenesis.

Far from being stamped from a common mold, like transistors, neurons display a dizzying variety of forms and functions. Researchers have discovered scores of distinct types of neuron just in the visual system. And let's not forget all the genes that are constantly turning on and off and thereby further altering the brain's operation.

Assuming that each synapse in the human brain processes ten action potentials per second and that these transactions represent the brain’s computational output, then the brain performs at least a quadrillion operations per second. Some supercomputers have already exceeded this information-processing capacity, encouraging claims by artificial-intelligence enthusiasts—notably Ray Kurzweil and other members of the Singularity cult--that computers will soon become vastly more intelligent than their creators.

But the brain may be processing information at many levels below and above that of individual neurons and synapses. Indeed, some researchers suspect that each individual neuron, rather than resembling a transistor, is more like a computer in its own right, engaging in complex information-processing. Moreover, brains may employ many different methods of encoding information.

The first neural-code candidate was discovered in the 1920s by the British neurophysiologist Edgar Adrian. When Adrian increased the pressure on tactile neurons, they fired at an increased rate. This so-called rate code has now been demonstrated in many different animals, including Homo sapiens. But a rate code is a crude, inefficient way to convey information, akin to communicating solely by humming at different pitches.

Neuroscientists have therefore long suspected that the brain employs subtler codes. In so-called temporal codes, information is represented not just in a cell’s rate of firing but in the precise timing between spikes. For example, whereas a rate code treats the spike sequences 010101 and 100011 as identical, a temporal code assumes that the two sequences have different meanings.

On a more macro level, researchers are searching for "population codes" involving the correlated firing of many neurons. The late Francis Crick favored a code involving many neurons firing at the same rate and at precisely the same time, a phenomenon called "synchronous oscillations." Others propose that information is carried not by spikes per se but by electromagnetic fields—generated by millions of electrochemical pulses--constantly sweeping through the brain.

So far, however, the evidence for any particular code remains tentative. The brain could utilize all these codes, or none. Complicating matters further, research on artificial cochleas and other prostheses suggests that brains may devise new codes in response to novel stimuli. Given all this confusion, you can see why some neuroscientists worry that cracking the neural code may take a long, long time. Maybe a century or longer.

Of all scientific fields, neuroscience has the most potential to produce revolutionary discoveries, with enormous philosophical as well as practical import. (Particle physics is so over.) Optimists will no doubt say that the Human Brain Project and the Brain Activity Map—by boosting funding and collaboration--might help us decipher the neural code, or codes. But I fear that these big, much-hyped initiatives will turn out to be as disappointing as the Decade of the Brain. Rather than boosting the status of neuroscience, they may harm its credibility.

Self-plagiarism alert: This post contains prose from several previous articles and from The Undiscovered Mind. These passages were so perfectly crafted that I didn't see any point in trying to improve upon them.

Image: Saad Faruque,Flickr.

Postscript: Some readers challenge my claim that the Human Genome Project "has failed to deliver any significant medical breakthroughs." Here's what Nicholas Wade of The New York Times, whose reporting on genetics is if anything excessively positive, said in 2010: "Ten years after President Bill Clinton announced that the first draft of the human genome was complete, medicine has yet to see any large part of the promised benefits. For biologists, the genome has yielded one insightful surprise after another. But the primary goal of the $3 billion Human Genome Project--to ferret out the genetic roots of common diseases like cancer and Alzheimer’s and then generate treatments--remains largely elusive. Indeed, after 10 years of effort, geneticists are almost back to square one in knowing where to look for the roots of common disease." Wade's assessment still holds. The Genome Project was supposed to lead to gene therapies that could cure or treat diseases stemming from genetic mutations. Last summer, European health officials approved a gene therapy for a lipid-related disorder that affects about one in a million people. So far, not a single gene therapy has been approved for commercial sale in the U.S. I reiterate: the Human Genome Project has failed to fulfill its promise, and it had a much stronger scientific foundation than the new brain projects. Do I oppose funding for genetics and neuroscience? Of course not. The potential of this research is so vast that we can never stop supporting it, even if payoffs are slow in coming. But precisely because the research is so vitally important, it should be marketed honestly.

Post-Postscript: Henry Markram, in a comment below, criticizes my criticism of the Human Brain Project, for which he is "Coordinator." He calls my views "nonsense" and "mind-boggling," and he urges me and other critics to "elevate your discussion a little--it sounds like the house of Babylon…and just maybe we can get out of the dark ages here." If I didn't know Markram's history, I might assume that his rant was posted by an imposter trying to make him look bad. But his comments recall his 2009 diatribe against Dharmendra Modha, leader of an IBM effort to model a cat brain. After Modha received some positive attention, Markram called the cat-brain model a "scam" that is "light years away from a cat brain, not even close to an ant's brain in complexity. It is highly unethical of Mohda to mislead the public in making people believe they have actually simulated a cat's brain. Absolutely shocking." Okay, Modha was guilty of hype. But Modha's hype pales beside that of Markram. Just months before he slammed Modha, Markram said at a TED Conference: "It is not impossible to build a human brain and we can do it in 10 years." He indulges in more hype in his comments below, calling the Human Brain Project "probably the most rigorously reviewed proposal in the history of grants." I find it, well, mind-boggling that the European Union has invested more than $1 billion in a project led by someone with so little credibility.

The views expressed are those of the author and are not necessarily those of Scientific American.

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