Cortical synchronization of neuron firing in multiple brain regions

September 21, 2010

Cortical oscillations can effectively rally groups of neurons in widely dispersed regions of the brain to engage in coordinated activity, researchers at the University of California, Berkeley have found.

“One of the key problems in neuroscience right now is how you go from billions of diverse and independent neurons, on the one hand, to a unified brain able to act and survive in a complex world, on the other,” said principal investigator Jose Carmena, UC Berkeley assistant professor at the Department of Electrical Engineering and Computer Sciences, the Program in Cognitive Science, and the Helen Wills Neuroscience Institute. “Evidence from this study supports the idea that neuronal oscillations are a critical mechanism for organizing the activity of individual neurons into larger functional groups.”

At UC Berkeley, neuroscientists examined existing data recorded over the past four years from four macaque monkeys. Half of the subjects were engaged in brain-machine interface tasks, and the other half were participating in working memory tasks. The researchers looked at how the timing of electrical spikes — or action potentials — emitted by nerve cells was related to rhythms occurring in multiple areas across the brain.

The timing of when individual neurons spiked was synchronized with brain rhythms occurring in distinct frequency bands in other regions of the brain. For example, the high-beta band — 25 to 40 Hz (cycles per second) — was especially important for brain areas involved in motor control and planning.It turns out that this local-to-global connection is vital for organizing spatially distributed neuronal groups.

“If neurons only cared about what was happening in their local environment, then it would be difficult to get neurons to work together if they happened to be in different cortical areas,” said study lead author Ryan Canolty, a UC Berkeley postdoctoral fellow. “But when multiple neurons spread all over the brain are tuned in to a specific pattern of electrical activity at a specific frequency, then whenever that global activity pattern occurs, those neurons can act as a coordinated assembly.”

The researchers pointed out that this mechanism of cell assembly formation via oscillatory phase coupling is selective. Two neurons that are sensitive to different frequencies or to different spatial coupling patterns will exhibit independent activity, no matter how close they are spatially, and will not be part of the same assembly. Conversely, two neurons that prefer a similar pattern of coupling will exhibit similar spiking activity over time, even if they are widely separated or in different brain areas.

The authors noted that this local-to-global relationship in brain activity may prove useful for improving the performance of brain-machine interfaces, or lead to novel strategies for regulating dysfunctional brain networks through electrical stimulation. Treatment of movement disorders through deep brain stimulation, for example, usually targets a single area. This study suggests that gentler rhythmic stimulation in several areas at once may also prove effective, the authors said.

The UC Berkeley findings are to be published the week of Sept. 20 in the online early edition of the journal Proceedings of the National Academy of Sciences.

More info: University of California – Berkeley news