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Science and the Environment
Tue June 17, 2014
Your Brain's Got Rhythm, And Syncs When You Think
Originally published on Wed June 18, 2014 3:47 pm
Even if you can't keep a beat, your brain can. "The brain absolutely has rhythm," says Nathan Urban, a neuroscientist at Carnegie Mellon University in Pittsburgh.
When you concentrate, Urban says, your brain produces rapid, rhythmic electrical impulses called gamma waves. When you relax, it generates much slower alpha waves.
The internal cadences of the brain and nervous system appear to play an important role in everything from walking to thinking, Urban says. And abnormal rhythms, he says, have been associated with problems including schizophrenia, epilepsy, autism and Parkinson's disease.
The rhythms of the brain begin with the firing patterns of individual brain cells. Some types of cells tend to fire as slowly as once a second, while others tend to fire more than a hundred times as fast. "They're little clocks," Urban says. "They have an intrinsic frequency."
All those different beats in the brain could produce chaos. One reason they don't is that groups of brain cells 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 and has found evidence that it works a bit like a room full of people clapping their hands. At first, each person claps to his own beat. But if you ask them to clap together, they'll start listening to their neighbors and adjusting their rhythms until the claps are synchronized.
Brain cells appear to do something very similar, Urban says. There's still debate about why this synchronization takes place. But many scientists believe it's important, because they know that when any two cells fire together, the connections between them get stronger, a process that is critical to learning and memory.
The Rhythms of Digestion and Dance
Of course, rhythms in the brain and nervous system also control many rhythms in the body. Among these rhythms are the repetitive muscle contractions responsible for functions as basic as digestion and as elevated as dance, says Eve Marder, a biology professor at Brandeis University. Marder has spent years studying the complex patterns of nerve cell firing that allow crabs to chew, filter and digest their food.
"It turns out that the stomach of a crab is a very, very complicated mechanical device," driven by the precisely choreographed contractions of 42 sets of muscles, Marder says. And the way a crab processes lunch has a lot in common with the way a ballerina does pliés, she says. Both actions rely on circuits of nerve cells that fire in a sequence, activating one muscle, then another, then another until the pattern repeats.
Rhythmic sequences are also required to move around, says Mark Churchland, a brain scientist at Columbia University. Walking, for example, requires repeatedly lifting a foot up, putting it down, and pushing it back. Fish swish a tail from side to side to swim. "It's sort of hard to imagine any way of doing continuous locomotion that wasn't built on a rhythmic underpinning," Churchland says.
Many of these rhythms are maintained by cells in the nervous system, not the brain, Churchland says. This means the brain can use a kind of shorthand to control motion. So instead of sending instructions for each muscle contraction needed to take a step, the brain sends a general command: "Activate the walking rhythm."
What's interesting, Churchland says, is that the brain may be using this rhythmic shorthand for some motions that don't appear rhythmic at all, like reaching. "You start with your hand in one place and you move your hand to another place. There's nothing rhythmic about that," he says.
But when Churchland took a closer look at reaching he found something really surprising. "That pattern of muscle activity is the sum of two rhythms," he says.
When Rhythms Go Wrong
Diseases including epilepsy, schizophrenia and Parkinson's can disrupt the brain's normal rhythms. People with Parkinson's disease, for example, tend to develop abnormal firing patterns in their brains that result in tremor and other difficulties with movement.
Surprisingly, these symptoms of Parkinson's are greatly reduced when patients respond to the external rhythms of music and dance. This transformation is easy to see at a studio in Silver Spring, Md., where Lucy Bowen McCauley teaches a dance class designed for people with Parkinson's.
When a half dozen of her students arrive for class, their steps are halting, their gestures visibly distorted by tremors. After some warm-up exercises, they make their way to folding chairs on the dance floor and sit. Then, as the sound of Ella Fitzgerald fills the room and McCauley calls out "heel, heel, heel, toe, toe, toe," the group begins tapping out the beat in unison.
"When we use music, these Parkinson's patients become dancers," McCauley says. "They look graceful and they can move in rhythm."
After class, some students talk about the role that rhythm plays in their disease. "My doctor says he can tell a Parkinson's tremor from any other kind," says Anne Davis, a retired teacher who's had the disease for more than 15 years. That's because the tremors of Parkinson's have their own distinctive rhythm, Davis says.
And a man-made rhythm has helped reduce her tremor, she says. It comes from an implanted deep brain stimulation device that sends high-frequency electrical impulses to the area causing her hands to tremble. Scientists think the fast pulses somehow override the much slower rhythm responsible for tremor.
Many Parkinson's patients also experience something called freezing — a temporary inability to initiate a movement like taking a step. "You're trying to go forward or sideways or whatever and your feet won't move," says Phyllis Richman, another student in the dance class and a former food critic for the Washington Post. "So then you fall," Davis adds.
But musical rhythms have a remarkable ability to help Parkinson's patients unfreeze, McCauley says. "Two times I've had people really have trouble walking down the hall to get to the class," she says. The solution: "We hum a tune. One time I did a march and one time I did a waltz. And we got in sync with the rhythm and they were able to get their feet to match."
Of course, dance doesn't halt the brain damage caused by Parkinson's. But McCauley's students say the rhythms of dance give them a respite from the abnormal brain rhythms of Parkinson's. "I come here because this is where I get joy," Davis says.
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?
HAMILTON: Urban says, now imagine that you ask people to clap together. They'll start listening to their neighbors and adjusting their rhythms.
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.
MARK 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.
JON 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")
FITZGERALD: (Singing) A-tisket, a-tasket, a brown and yellow basket. I sent a letter to my...
ROBERT SIEGEL, HOST:
You're listening to ALL THINGS CONSIDERED from NPR News. Transcript provided by NPR, Copyright NPR.