We can’t see it, but brains hum with electrical activity. Brain waves created by the coordinated firing of huge collections of nerve cells pinball around the brain. The waves can ricochet from the front of the brain to the back, or from deep structures all the way to the scalp and then back again.
Called neuronal oscillations, these signals are known to accompany certain mental states. Quiet alpha waves ripple soothingly across the brains of meditating monks. Beta waves rise and fall during intense conversational turns. Fast gamma waves accompany sharp insights. Sluggish delta rhythms lull deep sleepers, while dreamers shift into slightly quicker theta rhythms.
Researchers have long argued over whether these waves have purpose, and what those purposes might be. Some scientists see waves as inevitable but useless by-products of the signals that really matter — messages sent by individual nerve cells. Waves are simply a consequence of collective neural behavior, and nothing more, that view holds. But a growing body of evidence suggests just the opposite: Instead of by-products of important signals, brain waves are key to how the brain operates, routing information among far-flung brain regions that need to work together.
MIT’s Earl Miller is among the neuroscientists amassing evidence that waves are an essential part of how the brain operates. Brain oscillations deftly route information in a way that allows the brain to choose which signals in the world to pay attention to and which to ignore, his recent studies suggest.
Other research supports this view, too. Studies on people with electrodes implanted in their brains suggest brain waves, and their interactions, help enable emotion, language, vision and more.
When these waves are abnormal, brainpower suffers, studies find. Detailed looks at how the brain uses these waves raise the possibility of tweaking the signals with electrical nudges — interventions that could lead to therapies that can correct memory problems and mental illness, for instance. Already, early attempts have led to improvements in people’s memory.
Scientists are studying how oscillations generated by nerve cells affect brain function. Although the boundaries between different wave types can be fuzzy, these oscillations can be grouped by frequency.
Fast gamma waves have been linked to states of high attention. 30 to 80 Hz
Beta waves may be involved in movement and complex tasks such as memory and decision making. 12 to 30 Hz
The first neuronal oscillations discovered, alpha waves appear when a relaxed person closes his eyes. 8 to 12 Hz
Theta oscillations may help the brain sort information essential for navigation. 4 to 8 Hz
These insights about brain waves coincide with a shift in neuroscience away from a view that reduces the brain down to the behavior of single nerve cells, or neurons. That’s like thinking of the brain as “a giant clock, and if you figure out each gear, you’ll figure out the brain,” Miller says. But “it’s not just individual neurons in a giant clock. It’s networks interacting in a very dynamic, fluid way.”
Central to those interactions, Miller and others think, are coordinated brain waves. “The oscillations are the most powerful signal in the brain,” Miller says. “How could evolution not have taken advantage of that?”
In three recent papers, Miller and colleagues argue that two different types of brain waves — beta and gamma — work together to selectively choose the information that makes it into working memory. Gamma waves that cycle 30 to 80 times per second (30 to 80 hertz) help coordinate information streaming in from our senses — what we feel, see and smell. In contrast, slower 12 to 30 Hz beta waves are the messages that help keep us on task by guiding the brain toward the sensory signals worth paying attention to.
These two types of brain oscillations engage in a neural seesaw: When beta waves are strong, akin to a stereo blasting, gamma waves are weak, as if the volume had been dialed down, and vice versa. Miller and colleagues saw this push-and-pull action in the brains of monkeys with implanted electrodes as the animals completed a tricky memory task, one that required the monkeys to hold several pieces of information in their minds at the same time. The results were described January 26 in Nature Communications. “At all these complex decision points, you can see the beta and gamma doing this complex dance in a…
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