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friday :: april 28, 2006
   
 
how brain cells work: nerve cells talk in pairs

When a group of people tries to decide how to carry out an important task, it is sometimes said that the pivotal discussions do not happen in large, well-attended meetings, but in one-on-one conversations around the water cooler. It turns out that among individual neurons in our brains, the same may hold true.

Likening the process to the sort of casual conversations one might have at a cocktail party, William Bialek and his research team have found that retinal ganglion cells, the nerve cells along the back of our eyes that transmit visual signals to the brain, organize their actions based on communications they have with other individual cells rather than on group-style discussions. The findings, derived from experiments with and mathematical models of groups of 40 cells in the retinas of salamanders, could shed light on how brain cells work as a team.

'We have found that it is possible to understand the group behavior of neural cells based solely on knowledge of these pair interactions,' said Bialek, who wrote the research paper with Princeton colleagues Michael Berry, Ronen Segev and Elad Schneidman. 'From these pair-wise communications, a consensus emerges as to what message will be sent from the eye to the brain. But it comes from many small discussions, not one large one.'

'By eavesdropping on the 'conversations' of individual nerve cells, these researchers learned to predict how small groups of nerve cells in the eye would behave,' said biophysicist C. John Whitmarsh. 'This really is a fantastic result, and could help us understand how brain cells work together to make decisions.'

'It seems that cells at the cocktail party talk primarily, perhaps exclusively, in pairs alone. No one belongs to a group, or takes dictation from a leader, but everyone bases their behavior on what we might call 'informed pair conversations.' They participate in as many of them as they can, listen as much as they can, then act,' Schneidman said.

According to this analogy, the retinal cells would transmit messages based on the information culled from these 'conversations.' However, Bialek said, as at any party, there are subtleties at work as well. 'Just as you might know from past experience that you tend to sympathize with one party guest quite often, but are put off by another, the opinions you draw from different conversations are not all weighted equally,' he said. 'You might nod politely at one person's argument, while agreeing strongly with another, even though they had both come down on the same side of an issue. Nerve cells seem to react to one another in the same way.'

'The evidence pointed us to a more startling discovery, which is that buried in the apparent randomness there are subtle relationships between pairs in the group, and you can actually determine what the group's decision will be, based solely on an awareness of these relationships between pairs,' Berry said. 'Our model does not exclude the possibility that larger groupings within the 40 cells exist. What it shows is that either way, they do not need to be considered to predict the final outcome.' >from *Researchers find nerve cells talk in pairs*. April 20, 2006


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imago
>
it takes two to speak the truth one to speak and another to hear
Henry Thoreau

sonic flow
>
from the eye to the brain [stream]
from the eye to the brain [download]

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