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How the mind's switches were built

Nobel-winning biologist Sydney Brenner says "there are three important questions we have to answer if we want to understand biological complexity."

How do genes work? How is that genetic information translated into cell types that work together? And how did the process get that way?

During his talk at the "Open Questions in Neuroscience" symposium in Seattle today, Brenner outlined an example of how those questions might be addressed, with regard to eye function. "Cell types must be encoded in the genome in some way," he observed. He suggested that there are binary options on every step of that coding process to produce a cell that deviates from the default path.

The difficult trick is to map that "decision space" into a time frame for development as well as a 3-D structure for the different cell types. Right now, scientists are just in the beginning stages of that cross-mapping challenge. But the process by which rods and cones are made for the retina hint that binary coding is the way it's done, Brenner said. He pointed out that some people suffer from a genetic malady that leaves their retinas without rods. It turns out that they lack a transcription factor known as NRL.

"NRL is required to throw the switch," explained Brenner, a senior distinguished fellow at the Salk Institute for Biologicfal Studies. That coding switch could be one of the important factors in the machinery for making sure the right number of cells turn into rods. And its existence may suggest that the production of rods represents a departure from the "default path" for producing cones.

"Once upon a time, I will declare, the eye started out as a row of photoreceptor cells that were sensitive to blue light," Brenner said. As time and evolution went on, more switches were added to the genetic gadgetry. And based on how jellyfish "see," that appears to be a plausible route for evolutionary development, Brenner noted.

Those switches probably developed from snippets of DNA coding that were duplicated within the genome, and changed through eons of mutation and natural selection. Brenner suggested that the underpinnings of brain cell development could be traced by a close examination of those linked duplications, which he calls "krikologs."

Is a book of genesis written in our genome? What do you think? Feel free to add your comments below.

Stay tuned for more from the "Open Questions in Neuroscience" symposium, sponsored by the Allen Institute for Brain Science at Seattle's Experience Music Project and Science Fiction Museum. Join the Cosmic Log corps by signing up as my Facebook friend or hooking up via Twitter. And if you really want to be friendly, ask me about "The Case for Pluto."