June 10, 2008 Brainpower May Lie in Complexity of Synapses By NICHOLAS WADE
Evolution's recipe for making a brain more complex has long seemed simple enough. Just increase the number of nerve cells, or neurons, and the interconnections between them. A human brain, for instance, is three times the volume of a chimpanzee's. A whole new dimension of evolutionary complexity has now emerged from a cross-species study led by Dr. Seth Grant at the Sanger Institute in England. Dr. Grant looked at the interconnections between neurons, known as synapses, which until now have been regarded as a standard feature of neurons. But in fact the synapses get considerably more complex going up the evolutionary scale, Dr. Grant and colleagues reported online Sunday in Nature Neuroscience. In worms and flies, the synapses mediate simple forms of learning, but in higher animals they are built from a much richer array of protein components and conduct complex learning and pattern recognition, Dr. Grant said. The finding may open a new window into how the brain operates. "One of the biggest questions in neuroscience is to answer what are the design principles by which the human brain is constructed, and this is one of those principles," Dr. Grant said. If the synapses are thought of as the chips in a computer, then brainpower is shaped by the sophistication of each chip, as well as by their numbers. "From the evolutionary perspective, the big brains of vertebrates not only have more synapses and neurons, but each of these synapses is more powerful - vertebrates have big Internets with big computers and invertebrates have small Internets with small computers," Dr. Grant said. He included yeast cells in his cross-species survey and found that they contain many proteins equivalent to those in human synapses, even though yeast is a single-celled microbe with no nervous system. The yeast proteins, used for sensing changes in the environment, suggest that the origin of the nervous system, or at least of synapses, began in this way. The computing capabilities of the human brain may lie not so much in its neuronal network as in the complex calculations that its synapses perform, Dr. Grant said. Vertebrate synapses have about 1,000 different proteins, assembled into 13 molecular machines, one of which is built from 183 different proteins. These synapses are not standard throughout the brain, Dr. Grant's group has found; each region uses different combinations of the 1,000 proteins to fashion its own custom-made synapses. Each synapse can presumably make sophisticated calculations based on messages reaching it from other neurons. The human brain has about 100 billion neurons, interconnected at 100 trillion synapses. The roots of several mental disorders lie in defects in the synaptic proteins, more than 50 of which have been linked to diseases like schizophrenia, Dr. Grant said. Dr. Edward Ziff, a synapse expert at New York University, said Dr. Grant's work was the first in which synapses had been analyzed from a cross-species perspective. "I would say this work is unique," he said. "Grant's been a leader in making this type of analysis and he deserves a lot of credit for it, although a certain amount of guesswork is involved." ------------------------------------------- agi Archives: http://www.listbox.com/member/archive/303/=now RSS Feed: http://www.listbox.com/member/archive/rss/303/ Modify Your Subscription: http://www.listbox.com/member/?member_id=8660244&id_secret=106510220-47b225 Powered by Listbox: http://www.listbox.com
