Professor John Gabrieli, Bing Distinguished Lecture Series
By Christine VanDeVelde
The human brain only weighs a couple of pounds in an adult, but this amazing device has the ability to think, to let us move physically in the world, to produce consciousness and to feel emotions. Nevertheless, sometimes there are pitfalls in the functioning of the brain, patterns that actually hinder us in doing what we need and want to do. How understanding brain function can help overcome these pitfalls of brain circuitry was the subject of an address by professor John D. E. Gabrieli, given on May 27, 2004, as part of the Bing Nursery School Distinguished Lecture Series.
A cognitive psychologist and neuroscientist, Professor Gabrieli was one of the first to use the new neuroimaging technologies to visualize the development of brain functions that underlie the growth of mental capacities in children. In his talk, "Educating the Brain: Lessons from Brain Imaging," Gabrieli reviewed some of the recent studies that examine the neurosystems underlying reading in children and how variations in those systems can provide insight into such problems as dyslexia.
Children acquire language naturally through interacting with a parent and our brains are optimized through many years of evolution to do that. Those who study the development of language, seek to understand how children are so adept at understanding language. But reading is different. Reading is a challenge and in the world we live in, it is a portal to many other opportunities. Children must master reading in order to flourish.
While the brain has evolved to do many things in terms of thinking, language, and physical movement, one thing it has not evolved to do is read, noted Dr. Gabrieli. That's because visual communication is only about two thousand years old in our world and that is insignificant in terms of brain evolution. Text has only been widely available for about five hundred years, since the invention of movable type. Our brains evolved to listen to people who speak to us and to speak to other people, but not to decode black-and-white strokes. "Reading is a brilliant and beautiful creation of our culture that our brains have to somehow get around to understanding," said Gabrieli.
Dyslexia is an unexplained difficulty in reading that can't be accounted for by poor vision, lack of opportunity. Depending on your definition, it occurs in up to five to ten percent of the population. As Gabrieli noted, "It's unfortunately common for a child to experience some difficulty."
Today, the methods of modern cognitive neuroscience are helping us to understand more about how a child learns to read and maybe understand more about why it's difficult for some children. This, Gabrieli said, is enormously exciting. Optimally what researchers would like to be able to do is to measure the neurons that let us speak or read or listen or have feelings for people. But it's not possible to intervene that directly in the human brain. In order to be noninvasive, researchers interrogate the gossipy neighbors of neurons, that is, the vascular areas that surround neurons and that become active as different parts of the brain become engaged.
In his research, Dr. Gabrieli uses a standard MRI machine. Typically, children are asked to do something that will activate certain neurons in the brain, which then changes the blood flow and oxygenation in that area. That then changes the magnetic property of the brain and the naturally-occurring changes in the brain can be measured.
While most of us think of reading as primarily visual, in the brain it actually occurs as a result of both vision and hearing. We learn to read by picking up the sounds of language at home with our parents and other children, and then we somehow have to discover how those sounds map onto the letters, syllables and words of text. These symbols are pregnant with sound, but those sounds have to be discovered. This is called "phonemic awareness," the idea that these simple visual things carry sounds, and it's through knowing those sounds that the meanings of words are discovered.
English is especially tricky, even compared to other languages, for understanding this relationship between the sight of words and the sounds of language. What psychologists call the "irregularity of English" poses an extra challenge because it places an extra demand on the child to learn all the exceptions of the language.
According to Dr. Gabrieli, over a hundred years of neurology tell us two areas of the brain are essential for the comprehension and production of speech -- a frontal area, called Broca's area, is important for the production of speech. A posterior area, called Wernicke's area, is important for understanding what people are saying.
In a wide range of studies from many laboratories and in multiple nations, it has been shown that the biggest difference between good and bad readers is a difference in function in the area around Wernicke's area. Researchers have found that in children and adults who were poor readers and had been diagnosed with dyslexia, there was no activation at all in that region as they thought about the sounds of printed letters. This has important implications because it means that, for the vast majority of children, a very big part of their reading difficulty is not visual, but auditory.
Further, it has been found that for certain parts of auditory comprehension, for listening to the sounds of language, humans operate at an astoundingly high speed of information processing -- in the thousandths of a second range -- to achieve comprehension. Researcher Paula Tallal had the idea that for some children who are poor readers, the root of their difficulty might be not that they have trouble reading the text but that they have trouble with the sounds upon which you learn to read visual text. And the trouble with the sounds comes from difficulty in making rapid distinctions in the auditory speech stream.
Thus, there's a domino effect. First, these children never hear the sounds quite right. But they don't know that. They just hear what they hear and they don't know that other people are hearing, for example, "baa" and "daa" as distinct sounds. Tallal took children with language impairments, many of whom go on to be poor readers, and set up the following task. She played two tones -- a high and a low, or a low and a high. The child was simply asked to say which tone came first. And then the time between the two tones was varied. When the range of time between the two tones got to about a third of a second, the children with language impairments could no longer tell which tone came first. An inability to make these very rapid distinctions could be very problematic in language where you have to constantly make 40-millisecond distinctions.
To understand this phenomenon, Dr. Gabrieli suggested that we think of what it feels like when we have a second or third language in which we're not very fluent. It always seems as if people are speaking very quickly in that language. But they're not speaking quickly, we're just understanding really slowly.
It has also been found, both in adults and children, that there is a spot in the left frontal cortex of normal readers that was activated by the rapid sound. "It's as if this part of the brain automatically turns on when it hears a rapid sound or gets recruited to deal with a rapidly changing sound," noted Dr. Gabrieli. But in children who are poor readers, these areas in the brain are not responsive at all. It's not that they don't hear the sounds. But very well defined sounds are needed in order to map them onto printed text. If a child or adult is shaky on those sounds and has a hard time telling them apart, the visual reading that builds on that falls apart.
And there's further evidence in adults for the idea that parts of the brain that do the fastest processing are at risk even when reading or language are not involved. In an NIH experiment, a series of lines was moved, then stilled, then moved. In a healthy adult, a part of the brain turned on when there was motion, turned off when the motion ceased, then turned on again when the motion began again. These areas of the brain are specialized for motion processing and vision, a part of the brain that's very sensitive to movement. But when these series of black and white lines moved back and forth for adults who were poor readers, those parts of the brain didn't turn on at all. The test subjects weren't even looking at words, just lines moving back and forth. This research has led to the idea that some parts of our brain excel at doing things very fast, and those may not be optimal in individuals who struggle to read.
A similar study from the Psychology Department at Stanford found that the more activation you got in this part of the brain, the better the reader you were. So, Gabrieli said, there might be parts of our brain that are brilliant at being super fast, the information super-highways of the brain, that are essential for reading and these may be less well-tuned in children who go on to be poor readers.
The way we think of the difficulties in 80 percent of children who read poorly or who struggle to read, noted Gabrieli, is that they're really just at the tail end of a normal distribution. Probably they don't have anything that's significantly different about their brain. They just happen to be at the end of the spectrum for functions like rapid auditory processing. There is also growing evidence that there's a genetic link between reading difficulty and syndromes like attention deficit disorder. In fact, said Gabrieli, there's almost no doubt that genetics are a part of the reading puzzle.
One of the reasons for studying the brain is to discover markers in infants or preschool children in order to intervene before failure. Poor readers are now overwhelmingly discovered only through failure. "We can predict I think better and better and better which is the child who will struggle to read, and not only spare them hopefully the difficulty of failure, but discover a difficulty that needs to be dealt with," said Gabrieli.
He added, "We also have a suspicion that these children are bravely finding a way to read as best they can, and that strategy is not a good strategy, unfortunately. It doesn't take them very far, and by the time this child is a grade behind where they should be, they're not only not using the mechanisms in the brain that are optimal for reading, they've really worked hard to learn an alternate strategy that goes so far but then collapses. Then you have to simultaneously encourage them on a fruitful path to reading, but get them to stop using a reading method that they've been doing day in and day out for years. And we all know there's nothing harder to get rid of than a habit we engage in every day for hours."
In one program aimed at helping poor readers, researchers attempted to improve rapid auditory processing, so that a child could better appreciate sounds and then more easily map them onto words. They found that, as a result of improving auditory processing, the children became somewhat better readers -- commensurate with a gain in activation in that part of the brain that seems to be related to the growth of reading ability.
"So we're actually extremely optimistic that for many, many children the right kinds of interventions will actually be very potent and let them, if not become wonderful readers, be plenty good enough to do what they need to do and succeed where their strengths will allow them to flourish," said Gabrieli.
That said, Gabrieli noted that, in no case, is brain imaging yet at a point where it's a better diagnostic tool than analysis of behavior or standardized testing. Where are things going? To early investigations of biological markers and genetics that permit prediction of who will go on to struggle and allow experts to intervene in a positive and aggressive way, before the trouble arises through failure.
"The science will move fast," concluded Gabrieli. "Translating that into public policy, however, will be an uphill climb, as things usually are when contemplated on the large scale of education." Dr. Gabrieli received his B.A. from Yale and his Ph.D. in Behavioral Neurosciences from MIT. He joined the Department of Psychology faculty at Stanford in 1991 and is considered one of the university's most productive and visible young scientists and one of the world's leading researchers using the new neuroimaging technologies such as Functional Magnetic Resonance Imaging. His work has won him an Early Career Award in Neuropsychology from the American Psychological Association.