sábado, 2 de febrero de 2013

sábado, febrero 02, 2013


January 31, 2013 5:53 pm
 
We are not yet ready to simulate the brain
 
Europe’s billion-euro project is important but has an unrealistic goal, writes Gary Marcus
 

The 86 or so billion neurons in the human brain and the hundreds of trillions of connections between them allow us to think, walk, talk and interact with one another. It is no exaggeration to say all human nature lies within. The more we understand how it works, the better we can diagnose and treat neurological disorders from autism to Alzheimer’s.


The 10-year €1.19bn project to simulate the entire human brain, announced on Monday by the European Commission is, at about a sixth of the cost of the Large Hadron Collider, the biggest neuroscience project undertaken. It is an important, but flawed, step to a better understanding of the organ’s workings.


The flaw lies in the unrealistic goal. In the words of the science journal Nature, The Human Brain Project’s goal of a complete simulation is “a breathtaking ambition that has been met with some scepticism”. Although it would be valuableenabling researchers, for example, to test the effects of mental-health drugs – the complexity of the organ is far too intricate to be modelled accurately with today’s computers. By most estimates, this is likely to be out of reach for decades.


As neuroscientist Matteo Carandini recently observed, more than two decades of attempts to build simulations have yielded little, partly because complex systems are hard to model with sufficient precision (think about how hard it is to predict the weather two weeks hence). In the words of a classic 1972 essay by physicist P.W. Anderson: “The ability to reduce everything to simple fundamental laws does not imply the ability to start from those laws and reconstruct the universe ...


At each level of complexity entirely new properties appear.” Large-scale models are possible but the more complex they are, the greater the computational demands, and the greater the risk of error. Even if computer speed continues to double every 18-24 months, it is likely to take significantly more than a decade to reach the point at which an accurate, complete simulation is genuinely feasible.


And even if we had sufficient computing power, we do not know enough about how individual neurons work, either alone or in co-ordination with other neurons. We still lack basic knowledge, such as how memories are encoded in the brain, and it is hard to simulate what we do not understand.


Even so, it could foster a great deal of useful science. The crucial question is how the money will be spent. Much of the infrastructure developed will serve a vast number of projects, and the funding will support more than 250 scientists from more than 80 institutions, each with his or her own research agenda. A great many, such as Yadin Dudai (who specialises in memory), Seth Grant (who studies the genetics and evolution of neural function) and Stanislas Dehaene (who works on the brain basis of mathematics and consciousness), are stellar.


Still, by focusing on the newsworthy but unlikely goal of cataloguing all the brain’s individual parts, the project may squander some of its budget. By way of analogy, imagine a laptop fell to earth 500 years ago, and the world’s best scientists tried to discover how it worked. One strategy would be to dissect it, noting how the wires and transistors connect, developing tools such as microscopes and logic probes to try to fathom its complexity. Another would be to use the software to try to get a handle on what it did. One would hope to connect the two levels of understandingone functional (what the laptop does), the other physical (how the circuits work). It is doubtful one could recreate the laptop by taking measurements.


Contemporary neuroscience is filled with talk of axons, dendrites, neurotransmitters, and technical machinery such as calcium channels (which allow neurons to do their work). But too little is known about how those elements co-ordinate to mediate ideas, emotions and actions. Even basic phenomena such as short-term memory remain poorly understood. At present, the Human Brain Project seems too tilted towards physical understanding, with too little weight given to functional understanding. Truly understanding the brain will require bridging between the two.


The writer, author of ‘Guitar Zero’ and professor of psychology at New York University, writes on science and technology for NewYorker.com

 
Copyright The Financial Times Limited 2013.

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