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 In the brain, the number of neurons in a network may not matter

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Date posted: 04/02/2014

Last spring, President Obama established the federal BRAIN Initiative to give scientists the tools they need to get a dynamic picture of the brain in action.

To do so, the initiative’s architects envision simultaneously recording the activity of complete neural networks that consist of thousands or even millions of neurons. However, a new study indicates that it may be possible to accurately characterize these networks by recording the activity of properly selected samples of 50 neurons or less – an alternative that is much easier to realize.

The study was performed by a team of cognitive neuroscientists at Vanderbilt University and reported in a paper published the week of Feb. 3 in the online Early Edition of the Proceedings of the National Academy of Sciences.

The paper describes the results of an ambitious computer simulation that the team designed to understand the behavior of the networks of hundreds of thousands of neurons that initiate different body movements: specifically, how the neurons are coordinated to trigger a movement at a particular point in time, called the response time.

The researchers were surprised to discover that the range of response times produced by the simulated population of neurons did not change with size: A network of 50 simulated neurons responded with the same speed as a network with 1,000 neurons.

For decades, response time has been a core measurement in psychology. “Psychologists have developed powerful models of human responses that explain the variation of response time based on the concept of single accumulators,” said Centennial Professor of Psychology Gordon Logan. In this model, the brain acts as an accumulator that integrates incoming information related to a given task and produces a movement when the amount of information reaches a preset threshold. The model explains random variations in response times by how quickly the brain accumulates the information it needs to act.

Meanwhile, neuroscientists have related response time to measurements of single neurons. “Twenty years ago we discovered that the activity of particular neurons resembles the accumulators of psychology models. We haven’t understood until now how large numbers of these neurons can act collectively to initiate movements,” said Ingram Professor of Neuroscience Jeffrey Schall.

No one really knows the size of the neural networks involved in initiating movements, but researchers estimated that about 100,000 neurons are involved in launching a simple eye movement.

“One of the main questions we addressed is how ensembles of 100,000 neuron accumulators can produce behavior that is also explained by a single accumulator,” Schall said.

See the full Story via external site: news.vanderbilt.edu



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