Much of neuroscience, the study of the brain, is in the business of deconstruction – of reducing the brain into ever smaller parts: Regions, neurons, neural chemistry, molecular biology. This is vital research and a typical main path for many sciences. However, it’s not the only path. Another one leads in the other direction – understanding the integration of the brain. The brain is clearly more than the sum of its parts. It has billions of independent and varied neurons that somehow coordinate to react, act, and remember. It does this in milliseconds; speed is a matter of survival.
Over the years neurologists have learned that certain areas of the brain are associated with certain kinds of activity, for example monitoring the senses, regulating the body, and emotional response. It’s also known that most brain activity isn’t confined to these specific locales. When you see danger (a bear approaching) all kinds of responses are set in motion – instantly. Such responses involve nearly every part of the brain but are coordinated. That coordination, which is sophisticated in the details and obviously complex, baffles scientists.
By analogy the mystery of brain integration is a massive puzzle, a three-dimensional puzzle at that. One piece has just been identified: Researchers at the University of California Berkeley (USA) have found that the brain uses cortical rhythms, electrical oscillations operating at specific frequencies, to coordinate the work of many neurons in many different locations.
So yes, the brain’s got rhythm. The research, published in the September 20, 2010 online early edition of the journal Proceedings of the National Academy of Sciences (PNAS) [Oscillatory phase coupling coordinates anatomically dispersed functional cell assemblies] started from the observations of Donald Hebb who first described the concept of the brain coordinating ad-hoc groups of neurons to perform various functions. Hebb called these groups cell assemblies and considered them the most important unit of brain function.
To gain insight on how neuron assemblies might work; the Berkeley team sifted through four years of data from testing a group of four macaque monkeys. Specifically they were looking for the timing of electrical activity (action potentials) that occurred across multiple areas of the brain. They found there were identifiable timings at specific frequencies, for example, cortical oscillations at 25-40 hertz (cycles per second) were associated with brain areas active in motor control.
In essence, the neurons would ‘tune in’ to a specific frequency and become part of a functional network, which could involve neurons operating in many different locations in the brain. This is how neuron cell assemblies form. In this schema, neurons physically next to each other could, in fact, be operating in completely unrelated cell assemblies.
“It is like the radio communication between emergency first responders at an earthquake,” Canolty [UC Berkeley postdoc] said. “You have many people spread out over a large area, and the police need to be able to talk to each other on the radio to coordinate their action without interfering with the firefighters, and the firefighters need to be able to communicate without disrupting the EMTs. So each group tunes into and uses a different radio frequency, providing each group with an independent channel of communication despite the fact that they are spatially spread out and overlapping.”
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.
In some ways, this research begs more questions than it answers. How is it individual neurons recognize specific frequencies? Why those frequencies? How are the frequencies generated? What information, if any, is carried at those frequencies? How is the coordination achieved? The insight that the brain uses rhythms (frequencies) is an important first step – but only the first step – through a gateway to a much longer trail of research that will probably lead deep into the realm of molecular biology.