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See Inside November / December 2010

Neural Feedback: Brain Influences Itself with Its Own Electric Field

The brain generates an electric field that influences its own activity

Your brain is electric. Tiny impulses constantly race among billions of interconnected neurons, generating an electric field that surrounds the brain like an invisible cloud. A new study published online July 15 in Neuron suggests that the brain’s electric field is not a passive by-product of its neural activity, as scientists once thought. The field may actively help regulate how the brain functions, especially during deep sleep. Although scientists have long known that external sources of electricity (such as electroshock therapy) can alter brain function, this is the first direct evidence that the brain’s native electric field changes the way the brain behaves.

In the study, Yale University neurobiologists David McCormick and Flavio Fröhlich surrounded a still-living slice of ferret brain tissue with an electric field that mimicked the field an intact ferret brain produces during slow-wave sleep. The applied field amplified and synchronized the existing neural activity in the brain slice. These results indicate that the electric field generated by the brain facilitates the same neural firing that created the field in the first place, just as the cloud of enthusiasm that envelops a cheering crowd at a sports stadium encourages the crowd to keep cheering. In other words, the brain’s electric field is not a by-product; it is a feedback loop.

Although researchers knew that periods of highly synchronized neural activity (such as that of deep sleep) are crucial for maintaining normal brain function, exactly how these stable phases are coordinated—and why they go awry in dis­orders such as epilepsy—was never clear. The new study indicates scientists may find some answers in the surprisingly active role of the brain’s electric field.

“I think this is a very exciting new discovery,” says Ole Paulsen, a neuro­scientist at the University of Cambridge who was not involved in the study. “We knew that weak electric fields could impact brain activity, but what no one had really tested before was whether electric fields produced by the brain itself could influence its own activity.”

Fröhlich sees therapeutic applications as well, particularly in improving a promising technique called transcranial direct-current stimulation (tDCS), which applies weak electric fields to the scalp to treat, for example, depression and chronic pain. Traditionally tDCS uses standard electric fields that do not change much, as opposed to the dynamic electric fields used in the new study to mimic a living brain. “The next logical step is to use these more complex waveforms in a clinical setting and see if they improve the treatment,” Fröhlich says.

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