Designed to Speak Its Mind
The instinct for language is so ingrained in the human brain that there is almost no end to the ways it can articulate its inner voice, from the sounds of speech and the gestures of signed languages to the tactile alphabet of Braille, the clicks of Morse code and the cryptic symbols of computer data processing.
The brain, it seems, is designed to speak its mind.
Even so, precisely how this organ’s fragile tissue--billions of cells woven together by the moist threads of neural synapses--can communicate so fluently has eluded scientists searching for the biological roots of language.
In recent months, however, the effort to understand the anatomy of language has resulted in a series of discoveries of how every human brain overcomes its isolation to communicate its innermost desires, thoughts and intentions.
In work presented recently to the Society for Neuroscience, researchers at McGill University in Montreal showed that critical neural areas of the brain respond the same way whether words are spoken aloud or signaled silently with the hand gestures of sign language.
In fact, they found that the brains of deaf people who have used only sign language since birth responded to signed words in areas that had been thought to be devoted exclusively to speech.
“It suggests we have a brain mechanism here that will make language out of whatever it is presented,” said Joy Hirsch, a brain imaging expert at Memorial Sloan-Kettering Cancer Center in New York City who studies the biology of language. “So auditory input is not necessary.”
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From earliest infancy, language--perhaps the most definitive human characteristic--plays an enormous role in helping the brain take shape, researchers have discovered. Experimental psychologists at Johns Hopkins University in Baltimore recently demonstrated that 8-month-olds can remember the sound of spoken words for as long as two weeks, suggesting that they are already beginning to memorize the building blocks of language.
So important is human language that the communication centers of the brain are among the first neural structures to mature, new research shows, and the compulsion to communicate can spur dramatic rearrangements in how neural circuits function. Indeed, research by Hirsch at Sloan-Kettering this summer showed that the capacity to speak a second language is stored in different places in the brain, depending on when in life a person becomes bilingual.
Taken together, “this research will force us to recast our very ideas about the nature of language,” said Laura Ann Petitto, an expert on the neurobiology of language who conducted the McGill study. “It suggests a completely new understanding of what brain-based mechanisms underlie our species’ extraordinary capacity for language.”
Until recently, almost everything that was known about the human capacity for language was discovered through the study of the spoken word. Most researchers assumed that the ability to turn thoughts into language evolved from the ability to talk out loud.
Just as songbirds reach out to their own kind through distinctive melodies and whales communicate underwater with mournful-sounding calls, so the capacity for human language must arise directly from the ability to utter sounds, they believed.
But the McGill researchers have found instead that language may be rooted in the brain’s ability to make sense of specific patterns that are found in all human languages.
They found that the neural appetite for meaningful communication is so strong that parts of the cerebral cortex might be dedicated to processing the patterns of natural language, whether or not they are encoded in sound.
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In their effort to understand the anatomy of language, Petitto, director of McGill’s laboratory for language, sign and cognition, and her colleagues at the Montreal Neurological Institute used positron emission tomography (PET) to study how deaf people and people with normal hearing process words.
PET scans allow scientists to study brain responses by taking pictures of neural blood flow and metabolic activity as a person performs different mental tasks.
The researchers wanted to know whether there were any differences in brain activity between those who developed language in the absence of sound--people born profoundly deaf who learned to sign as their native language--and those who learned to communicate through more conventional speech.
“We used the existence of signed languages as a research tool to explore the underlying basis for the neuroanatomical organization of language in all brains,” Petitto said.
Their findings suggest that the brain can reorganize itself depending on what kind of language an infant is taught.
Indeed, Petitto’s earlier studies of deaf infants exposed to sign language showed that they mastered language in much the same way and at the same pace as children who learn a spoken tongue.
Both groups start to experiment with single syllables between 7 and 10 months of age and begin to use their first words between 11 and 14 months, Petitto discovered. She even found that deaf babies exposed to sign language babble with their hands in the same manner that babies with normal hearing practice nonsense syllables aloud.
The developmental similarities, she said, are “surprising, because natural sign languages don’t involve speech production, and they don’t involve sound production.”
“Something about natural language and our capacity for language,” she said, “exists in addition to our capacity for speaking.”
