Daniel Stolte - How the Brain Strings Words Into Sentences

This press release from the University of Arizona reveals some new research on how the brain makes sentences from single words. Brain imaging has made this process visible (or possibly visible) for the first time.

How the Brain Strings Words Into Sentences

Using magnetic resonance imaging of the brain, researchers can visualize the two main language processing regions, Broca's region (yellow) and Wernicke's region (purple). (Image: Stephen Wilson)

By Daniel Stolte, University Communications, November 23, 2011

Distinct neural pathways are important for different aspects of language processing, researchers have discovered, studying patients with language impairments caused by neurodegenerative diseases.

While it has long been recognized that certain areas in the brain's left hemisphere enable us to understand and produce language, scientists are still figuring out exactly how those areas divvy up the highly complex processes necessary to comprehend and produce language.

Advances in brain imaging made within the last 10 years have revealed that highly complex cognitive tasks such as language processing rely not only on particular regions of the cerebral cortex, but also on the white matter fiber pathways that connect them.

"With this new technology, scientists started to realize that in the language network, there are a lot more connecting pathways than we originally thought," said Stephen Wilson, who recently joined the University of Arizona's department of speech, language and hearing sciences as an assistant professor. "They are likely to have different functions because the brain is not just a homogeneous conglomerate of cells, but there hasn't been a lot of evidence as to what kind of information is carried on the different pathways."

Working in collaboration with his colleagues at the UA, the department of neurology at the University of California San Francisco (UCSF) and the Scientific Institute and University Hospital San Raffaele in Milan, Italy, Wilson discovered that not only are the connecting pathways important for language processing, but they specialize in different tasks.

Assistant professor Stephen Wilson studies how the brain processes language by combining brain imaging with performance-based language tests. (Photo: D. Stolte/UANews)

Two brain areas called Broca's region and Wernicke's region serve as the main computing hubs underlying language processing, with dense bundles of nerve fibers linking the two, much like fiber optic cables connecting computer servers. But while it was known that Broca's and Wernicke's region are connected by upper and a lower white matter pathways, most research had focused on the nerve cells clustered inside the two language-processing regions themselves.

Working with patients suffering from language impairments because of a variety of neurodegenerative diseases, Wilsons' team used brain imaging and language tests to disentangle the roles played by the two pathways. Their findings are published in a recent issue of the scientific journal Neuron.

"If you have damage to the lower pathway, you have damage to the lexicon and semantics," Wilson said. "You forget the name of things, you forget the meaning of words. But surprisingly, you're extremely good at constructing sentences."

"With damage to the upper pathway, the opposite is true; patients name things quite well, they know the words, they can understand them, they can remember them, but when it comes to figuring out the meaning of a complex sentence, they are going to fail."

The study marks the first time it has been shown that upper and lower tracts play distinct functional roles in language processing, the authors write. Only the upper pathway plays a critical role in syntactic processing.

Wilson collected the data while he was a postdoctoral fellow working with patients with neurodegenerative diseases of varying severity, recruited through the Memory and Aging Center at UCSF. The study included 15 men and 12 women around the age of 66.

Unlike many other studies investigating acquired language disorders, which are called aphasias and usually caused by damage to the brain, Wilson's team had a unique opportunity to study patients with very specific and variable degrees of brain damage.

"Most aphasias are caused by strokes, and most of the strokes that affect language regions probably would affect both pathways," Wilson said. "In contrast, the patients with progressive aphasias who we worked with had very rare and very specific neurodegenerative diseases that selectively target different brain regions, allowing us to tease apart the contributions of the two pathways."

To find out which of the two nerve fiber bundles does what in language processing, the team combined magnetic resonance brain imaging technology to visualize damaged areas and language assessment tasks testing the participants' ability to comprehend and produce sentences.

"We would give the study participants a brief scenario and ask them to complete it with what comes naturally," Wilson said. "For example, if I said to you, ‘A man was walking along the railway tracks. He didn't hear the train coming. What happened to the man?' Usually, you would say, ‘He was hit by the train,' or something along those lines."

"But a patient with damage to the upper pathway might say something like 'train, man, hit.' We found that the lower pathway has a completely different function, which is in the meaning of single words."

To test for comprehension of the meaning of a sentence, the researchers presented the patient with a sentence like, "The girl who is pushing the boy is green," and then ask which of the two pictures depicted that scenario accurately.

"One picture would show a green girl pushing a boy, and the other would show a girl pushing a green boy," Wilson said. "The colors will be the same, the agents will be the same, and the action is the same. The only difference is, which actor does the color apply to?"

"Those who have only lower pathway damage do really well on this, which shows that damage to that pathway doesn't interfere with your ability to use the little function words or the functional endings on words to figure out the relationships between the words in a sentence."

Wilson said that most previous studies linking neurodegeneration of specific regions with cognitive deficits have focused on damage to gray matter, rather than the white matter that connects regions to one another.

"Our study shows that the deficits in the ability to process sentences are above and beyond anything that could be explained by gray matter loss alone," Wilson added. "It is the first study to show that damage to one major pathway more than the other major pathway is associated with a specific deficit in one aspect of language."

The study was primarily funded by grants from the National Institutes of Health and included the following co-authors: Sebastian Galantucci, Maria Carmela Tartaglia, Kindle Rising, Dianne Patterson (both at the UA's department of speech, language and hearing sciences), Maya Henry, Jennifer Ogar, Jessica DeLeon, Bruce Miller and Maria Luisa Gorno-Tempini.

Dharma Quote: Rain might be falling for ten thousand years, yet if our cup is upside down it will remain empty.

THE THIRD KARMAPA'S MAHAMUDRA PRAYERby Tai Situ Rinpoche trans. & ed. by Rosemarie Fuchsmore...

Dharma Quote of the Week

It is very difficult to help somebody overcome his or her problems when the problems are unstructured, when in a certain way this person does not have any problems, though deep inside all the problems are there. It is very difficult for a human being whose problem is confused, whose ego is ill-defined and without foundation, to really purify, clarify, and develop anything.

The same principle applies to praying. As long as we have our self, our ego, we pray to the Buddha: "Please bless me so that my prayers for the benefit of all sentient beings be fulfilled." Otherwise our prayer does not follow any line or direction. It would be like going to a big five-star hotel with five hundred rooms and not knowing your room number, or taking an elevator without knowing which floor to go to--this would be a big problem.

This is the reason for calling upon the great compassion of the Buddha and asking him to consider our prayers. The reason is not that the Buddha only listens to someone who prays to him; rather, without praying to the Buddha we are not developed enough to have the condition necessary to receive his blessing. Rain might be falling for ten thousand years, yet if our cup is upside down it will remain empty. Through praying we open up, we turn our cup to let the water get inside. (p.48)

 --from The Third Karmapa's Mahamudra Prayer by the XII Khentin Tai Situpa Rinpoche, translated and edited by Rosemarie Fuchs, published by Snow Lion Publications
The Third Karmapa's Mahamudra Prayer • Now at 5O% off!
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The Design of the Brain by Evan Lerner

From Print Magazine, this article takes a look at the human brain in terms of design - and the fact that the brain was not designed. Lerner mentions Kluge: The Haphazard Evolution of the Human Mind, by Gary Marcus, a cogent argument that the brain is not designed and is basically a collection of adaptations.

The Design of the Brain

by Evan Lerner

A look at the design of something that wasn’t designed at all.

Since you are reading this sentence, I will make a bold assumption and assert that you have a brain. This is neither sarcasm nor a metaphoric comment on your intellect or taste; this is about the roughly three pounds of squishy tissue between your ears.

Game show fans already have an inkling as to why; IBM finally showed off its natural-language-processing computer Watson on the game show Jeopardy! in February, where it demolished its fleshy opponents. That humanity could only sheepishly grumble about the computer’s buzzer reflexes is a tacit admission that it could basically read and understand the game’s clues as well as any human.

But this is only a bold, and not totally foolish, assumption under certain definitions of the word “read,” since computer programs have been scanning and memorizing this text long before it hit your optic nerves. In fact, everyone involved in the production of this article depends on that ability to effortlessly recall each character and the order it was entered, and to rearrange them into previous patterns at our discretion.

And while they might be able to read, what our computers have no hope at doing—and what Watson is perhaps only scratching the surface of—is coming up with the idea for this article in the first place. So far, the only machine we know capable of that kind of creative behavior is not the product of decades of meticulous engineering, but millennia of haphazard biological evolution. The brain wasn’t designed to think, analyze, or create. It wasn’t designed at all.

But that the brain is the only thing on the planet that can surprise its owner with a novel idea is one of our biggest unanswered scientific questions. What makes us more than meat-machines, programmed to sing, dance, and dream? What makes us human?

The Undesigned

The basic building blocks of the brain are neurons, long, branching cells that communicate with each other via electrochemical signals. The human brain has roughly 100 billion of them, or more than ten times the number of people on the planet. The organism with the simplest nervous system, the nematode, has 302.

To be totally reductionist, everything that happens in the brain can be boiled down to electrical signals in these neurons. The electrical signals cause chemicals known as neurotransmitters to jump the tiny gulf separating a neuron from one neighbor or another, which sets off new electrical signals in the recipient, and so on until you wiggled your left big toe or selected the next word in your sonnet. The difference lies in the pattern of neurons firing and the path through the various parts of the brain that pattern takes.

This process is more or less identical in humans and nematodes, as both species’ neurons are the product of the same slow, incremental changes of evolution. What separates the two species’ nervous systems can be traced back to surviving in the environments of our ancestors and those of a millimeter-long roundworm. Nematodes’ neural development could stop once life’s most basic functions—breathing, eating—were satisfied. The human hindbrain takes care of those, but to get to complex sensory processing, and then to poetry, painting, and neuroscience, the midbrain and forebrain needed to develop on top of it.

But when we concern ourselves with those uniquely human abilities, we’re really talking about the part of the forebrain known as the cerebral cortex and its Frontal, Parietal, Occipital, and Temporal lobes. Broadly speaking, they are respectively the centers of decision-making, spatial perception, vision, and speech. Of course, the actual mechanisms of all of the above involve both higher specialization within each of those lobes and interactions with many other parts of the brain.

The organization, interactions, and specificity of these regions seem so orderly, in fact, that it is tempting to think of them as being designed for their various purposes. But not only did these structures arise from the ground up, through millions of random mutations rather than a concerted effort, they did so in an environment that was largely devoid of the things we think they’re so purpose-built to interact with. To say there’s a part of the brain design for reading ignores the fact that there was nothing to read at the point it tookthe shape it has today.

“I think part of what designers do is try to reverse engineer the human mind to find out what kinds of things will tickle the brain,­­­­­” says Gary Marcus, professor of psychology at New York University, and author of Kluge, an account of the brain’s haphazard evolution. “I don’t think there’s a simple formula for it, because the brain itself is not a particularly simple system.”

In Kluge, Marcus outlines two overlapping thinking systems that evolution bestowed upon the brain: deliberative and reflexive. In the environment these systems evolved, both were useful—you’d need to deliberate with your fellow proto-humans about how to best corner your prey in order to eat, but allow your reactive systems to override your hunting strategy if you suddenly thought youmight be the one on the menu.

There's much more - read the whole article.

Tags: brain, evolution, design, structure, Kluge, Gary Marcus, The Design of the Brain, Evan Lerner, Print Magazine, Watson, artificial intelligence, neurons, neuroscience