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MELISSA BLOCK, HOST:

Today in our series, Rhythm Section, we're going to delve into the biological cadences of living creatures. NPR's Jon Hamilton explains how beats in the brain contribute to everything from walking to thinking.

LUCY BOWEN MCCAULEY: Here we go.

JON HAMILTON, BYLINE: In a dance class in Silver Spring, Maryland, Lucy Bowen McCauley is helping her students keep the beat.

(SOUNDBITE OF SONG, "A-TISKET, A-TASKET")

ELLA FITZGERALD: (Singing) A brown and yellow basket...

MCCAULEY: Now, let's do two heels. Up, down, up.

(SOUNDBITE OF SONG, "A-TISKET, A-TASKET")

FITZGERALD: (Singing) I sent a letter to...

HAMILTON: A half dozen bodies move in time with the music. And if you can look inside the brains of these dancers, you would see clusters of motor neurons firing in sync with Ella Fitzgerald.

(SOUNDBITE OF SONG, "A-TISKET, A-TASKET")

FITZGERALD: (Singing) A little girly picked it up and put it in her pocket...

MCCAULEY: Five, six, seven. Tap your heel.

HAMILTON: Our brains have lots of these internal beats.

NATHAN URBAN: The brain absolutely has rhythm.

HAMILTON: Nathan Urban is a neuroscientist at Carnegie Mellon University in Pittsburgh.

URBAN: So for example, if you're concentrating, high-frequency oscillations - so-called gamma frequency oscillations - turn out to be very important. In other contexts, lower frequency oscillations become more and more important.

HAMILTON: Urban says all of these oscillations - these rhythmic electrical patterns - begin with individual cells. He says every cell in the brain has its own beat.

URBAN: They're little clocks. They have an intrinsic frequency.

HAMILTON: Some fire once every second. Others, up to 200 times a second. All those different beats could produce chaos. One reason they don't is that groups of brain cells tend to synchronize when they need to get something done. So when a mouse is exploring a new place, cells begin firing together in areas of the brain involved in navigation and memory. Urban has been studying how brain cells achieve this synchrony. He thinks it works something like this.

URBAN: Imagine you have a room full of people, and you ask them to start clapping, OK?

(APPLAUSE)

HAMILTON: Urban says, now imagine that you ask people to clap together. They'll start listening to their neighbors and adjusting their rhythms.

(SYNCHRONIZED APPLAUSE)

HAMILTON: Urban says brain cells appear to do something very similar when they need to work together, and brain rhythms often control body rhythms. Eve Marder, at Brandeis University, records and studies the electrical activity in nerve cells that produce repetitive muscle movements in crabs.

EVE MARDER: If you walked into my laboratory, and if I took the electrical recordings and plugged them into an audio monitor, you would hear something like, brrr, brrr, brrr, brrr.

HAMILTON: That's the firing pattern that controls a crab's digestive system.

MARDER: It turns out that the stomach of a crab is a very, very complicated mechanical device.

HAMILTON: It doesn't just digest food. It also chews it and filters it. This requires the crab's nervous system to coordinate 42 different sets of muscles.

MARDER: So it's really sort of a biomechanical wonder.

HAMILTON: And Marder says the way a crab processes lunch has a lot in common with the way a ballerina does plies. Both actions rely on circuits of nerve cells that fire in a sequence.

MARDER: So that you get a one, two, three - one, two, three - one, two, three. Muscle one, muscle two, muscle three - muscle one, muscle two, muscle three - patterns of movement.

HAMILTON: Necessary for both digestion and dance. Mark Churchland at Columbia University says, rhythmic sequences are also needed for pretty much any form of locomotion.

MARK CHURCHLAND: You sort of have no choice but to move somewhat rhythmically, right? You need to put your foot down, push it back, lift it up, put it down, push it back again. Or, you know, if you're a fish, you swish your tail to the side. It's got to come back again. It's just sort of very hard to imagine any way of doing continuous locomotion that wasn't built on a rhythmic underpinning.

HAMILTON: Churchland says the brain appears to use rhythms as a kind of shorthand. Instead of sending instructions that include each muscle contraction needed to take a step, it just says, activate the walking rhythm. What's interesting, he says, is that the brain seems to use this rhythmic shorthand for some motions that don't appear rhythmic at all, like reaching.

CHURCHLAND: You start with your hand in one place, and you move your hand to another place. There's nothing rhythmic about that.

HAMILTON: But when Churchland took a closer look, he found something really surprising.

CHURCHLAND: That pattern of muscle activity is the sum of two rhythms.

HAMILTON: Churchland says certain brain rhythms are problem. For example, people with Parkinson's disease tend to develop abnormal patterns associated with severe tremor.

CHURCHLAND: Clearly, they have a pathological rhythm that is, you know, large enough and strong enough to be quite harmful.

HAMILTON: And that brings us back to Lucy Bowen McCauley's dance class.

(SOUNDBITE OF SONG)

HAMILTON: This is a class specifically for people with Parkinson's. Anne Davis is a retired teacher who's had the disease for more than 15 years.

ANNE DAVIS: You'll notice I'm holding my hands behind my back.

HAMILTON: To hide her tremor. Davis says, Parkinson's has given her lots of reasons to think about rhythm and the brain.

DAVIS: My doctor says he can tell a Parkinson's tremor from any other kind. And that's rhythm in itself, so that's pretty interesting.

HAMILTON: A few months ago, Davis had surgery to implant a device that sends high-frequency electrical impulses to the part of the brain causing her tremor. Scientists think the fast pulses somehow override the much slower rhythm that makes her hands shake. Deep brain stimulation also can help Parkinson's patients with what's called freezing. Davis asks her friend and classmate, Phyllis Richman to help describe what that is.

PHYLLIS RICHMAN: You're trying to go forward or sideways or whatever, and you're feet won't move.

DAVIS: So then, you fall.

HAMILTON: But musical rhythms have a remarkable ability to help Parkinson's patients unfreeze. Lucy Bowen McCauley says she's seen that herself.

MCCAULEY: Two times, I've had people really have trouble walking down the hall to get to the class. And I've gone in the lobby, and we hum a tune, and I hang onto their arm. And one time, I did a march. One time, I did a waltz. And we got in sync with the rhythm, and they were able to get their feet to match.

HAMILTON: Of course, dance doesn't halt the brain damage caused by Parkinson's. But McCauley says, it does offer people a temporary respite from their symptoms.

MCCAULEY: When we give them images and warm-ups and use music, these dancers - these Parkinson patients become dancers. And they look graceful, and they can move in rhythm.

HAMILTON: Anne Davis puts it another way.

DAVIS: I come here because this is where I get joy, and almost nowhere else, when you think about it.

HAMILTON: Thanks to the rhythms in her brain. John Hamilton, NPR News.

MCCAULEY: Oh, you're so musical, you guys. Thank you so much.

(SOUNDBITE OF SONG, "A-TISKET, A-TASKET")

(APPLAUSE)

(APPLAUSE)

FITZGERALD: (Singing) A-tisket, a-tasket, a brown and yellow basket. I sent a letter to my...

ROBERT SIEGEL, HOST:

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