What crying baby mice could teach us about human speech
Scientists have found a cluster of rhythmic brain cells in newborn mice that may explain why spoken languages around the world share a common tempo.
MARY LOUISE KELLY, HOST:
Next, a study about crying mice may help explain how humans learn to speak. NPR's Jon Hamilton reports that researchers have identified brain circuits that appear to synchronize the rhythms of vocal sounds and breathing.
JON HAMILTON, BYLINE: It takes human babies a year or so to start talking, but they arrive knowing how to call for help.
(SOUNDBITE OF BABY CRYING)
HAMILTON: Dr. Kevin Yackle of the University of California San Francisco says newborn mice also cry.
KEVIN YACKLE: They're ultrasonic vocalizations - have to use, you know, special microphones to hear them.
HAMILTON: Or be a mouse - Yackle says baby mice make these distinctive squeaks anytime they get separated from their mother.
YACKLE: We call it cries because the ultimate purpose of it is to have the mom find them and take them back to the nest.
HAMILTON: So Yackle's team began analyzing those cries.
YACKLE: We saw that within a single breath, there could be multiple cries. And when these occurred, they were occurring in a rhythm.
HAMILTON: A lot like the cries of a human baby.
(SOUNDBITE OF BABY CRYING)
HAMILTON: Yackle suspected that both species possess a brain circuit that produces rhythmic crying.
YACKLE: So then the question was, can we find the origin of this cry rhythm?
HAMILTON: In mice - to find out, they traced the signals that control muscles involved in vocalization. Then they looked for places in the brain that contains cells involved in crying and cells involved in breathing.
YACKLE: There really is only one area in the brain stem that has an overlap. And so this is what really quickly caught our attention to this - I call it a node or cluster of cells.
HAMILTON: Presumably the origin of the cry rhythm - to make sure, the team removed these cells from some mice. Those animals stopped producing cries or made cries that lacked rhythm. Yackle says in other animals, the team delivered tiny pulses of electricity to the cells.
YACKLE: You give them a very short pulse of stimulation, and they'll produce, you know, seconds of cries.
HAMILTON: Which is like minutes of wailing in a human baby - the results appear in the journal Neuron. And David Poeppel of New York University and the Max Planck Institute says the finding might help explain something that has puzzled scientists.
DAVID POEPPEL: When you actually do the math and you characterize signals very carefully, speech across all languages and across speaking styles is way more regular than we thought.
HAMILTON: We all tend to produce about three to six syllables each second. Poeppel says we seem to have an innate rhythm to our speech, and it could be because our brains still use a circuit found in mice.
POEPPEL: Our words come out as a string of sound, but you have to break it up into little parts. And how are those little parts generated? And that's what this study contributes to.
HAMILTON: Poeppel says humans quickly learn to control both their speech and their breathing.
POEPPEL: So you can inhale deeply and then say just ba (ph). So that's one syllable in one breath. But you can also inhale and go ba, ba, ba, ba, ba, ba, ba, ba, ba, ba, ba. So maybe that's 10. So there is a way to coordinate your breathing and your vocal output.
HAMILTON: Within limits - Poeppel says what's still a mystery is how we progress from crying babies to speaking adults. Maybe we learn to override those rhythmic brain circuits as we get older, or maybe we stop using them entirely. Poeppel says those questions can't be answered by studying mice.
POEPPEL: Is it a simple leap from mouse to marmoset, to a non-human primate and then to the human brain? No.
HAMILTON: But Poeppel says mouse studies like this one can help scientists figure out what brain circuits to look for in other species.
Jon Hamilton, NPR News.
(SOUNDBITE OF MURA MASA'S "SUICIDE BLADES") Transcript provided by NPR, Copyright NPR.