On the Human Condition
Volume XXVIII Number 2
Photo © Tyagan Miller
When the fMRI machine is in use, images are projected onto a screen (see above photo) behind the head of a volunteer subject lying inside the bore of the machine. The subject views the images through amirror attached to the head coil.
Photo courtesy IUB Department of Psychological and Brain Sciences
Tracking Your Brain in Real Time
Answer this: "The day after my favorite day is two days after Thursday. When is my favorite day?"
Got it yet? The answer is . . . well, the answer isn't important, as far as Sharlene Newman is concerned. What interests her is what's happening in your brain as you try to solve the riddle.
Newman, a cognitive scientist at Indiana University Bloomington, studies brains in action. She uses three important tools for this work: a truck-sized magnet, computers packed with data-crunching power, and a deep curiosity about how things work.
Locked inside a specially shielded and reinforced room, a gleaming white fMRI machine sits on the first floor of the IUB Psychology Building. The centerpiece of the brand-new IU Imaging Research Facility (directed by Newman's colleague Associate Professor of Psychology Julie Stout), the machine holds an eight-ton, three-tesla monster magnet. (A tesla is a measurement of magnetic intensity; three teslas is about twice as strong as a magnet found in a typical hospital MRI machine.) The "f" in fMRI stands for "functional"--unlike medical magnetic resonance imaging, fMRI goes beyond static images of anatomy or tissue to capture brain functioning as it occurs, in "real time." Basically, an fMRI machine generates a map of the brain at work by measuring not blood rushing to our heads, but inside them.
Think of it as a "brain blush." An fMRI image reflects hemodynamic responses, which means it shows where blood flows when we use our brain during a given task. "Whenever any tissue activates, it metabolizes oxygen," Newman explains, "so there is an increase in the flow of blood to that tissue [to provide blood oxygen]. FMRI measures changes in blood oxygen levels." As the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain puts it on its Web site (www.fmrib.ox.ac.uk/), "we do ‘blush' with thought. Increases in the blood supply to the brain ensure an adequate supply of oxygen to regions working harder in thinking."
When the brain works hard, the intensity of the electrical signals it emits increases as well. Those signal changes are tracked by the fMRI machine. "When you lie inside a strong magnetic field, your atoms and electrons align with that field," Newman explains further. "The fMRI machine transmits radio frequency pulses to disrupt that alignment, then we measure the speed as the electrons realign with the magnetic field."
One fMRI scan might collect data from the entire brain in a second. Newman got her start in neuroscience by processing the huge amount of raw data generated by multiple fMRI scans. With a background in electrical engineering and mathematics, she excelled at the necessary technical skills and knowledge of physics needed. But soon enough, she says, her interests shifted to the brain itself. It wasn't that big a leap, really--the engineer in her considers the brain just another kind of machine.
"I think of the brain as a black box," Newman says. "You know what goes in, and you can measure what comes out, so what's going on inside that box? That's what I'm interested in figuring out: how we work, how we think, how the brain is able to do all that it does."
When most of us think of a brain scan, we picture a 3D image glowing with vividly colored spots. Those spots indicate what parts of the brain are working--hearing highlights regions along the side of the brain, for example; vision lights up the occipital area at the back. The colorful images are generated by, as Newman jokingly calls them, "blob people." Newman is not a blob person.
She admits that the colors (which are arbitrarily assigned) make pretty pictures, but in her view, the blobs fall short of conveying what is happening when we think. "The blobs do tell us what region of the brain is involved, but they don't say how it is involved, what it is doing, or when it is doing it," she says.
Newman is particularly interested in the "when"--the synchronization of different brain regions as they become more, or less, active, depending on the mental load. "What we care about in my lab is how the hemodynamic responses, the changes in concentration of oxygen, go up and down with demand," she says. "From the blobs, which indicate activation, we extract time courses [brief intervals of time that show a change in signal intensity]." Looking at the timing of signal changes allows Newman to interpret more closely which brain regions are at work when and what functions those different regions fulfill.
In a recent pilot study, for example, Newman tested language processing and working, or short-term, memory. Subjects were presented with sentences that had either a simple or convoluted arrangement of words (e.g. "the reporter attacked the senator and admitted the error" or "the reporter that the senator attacked admitted the error"). The sentences were followed by comprehension questions asking who did what to whom ("the senator attacked the reporter, T/F"). The sentences also were presented to subjects all at once and one word at a time.
Her results are preliminary, but Newman says when the harder sentences were presented as a whole, the fMRI scans revealed "syntactic complexity effects"--in other words, certain regions of the brain worked hard to untangle the meaning. But when either kind of sentence was presented one word at a time, those same regions showed little activation. That's because working memory was on overload, she says.
"When you receive one word at a time, you can't process a sentence's syntax while you are also trying to buffer the words. You have to push that processing off until after the whole sentence is presented," she says.
Newman examined not only what happened mentally when the sentences were presented, but also what went on when subjects answered comprehension questions and what happened during the delay between the sentence delivery and the comprehension question. By isolating the time courses of the fMRI signals, she discovered that during the delay, the signals in certain areas did not relax, meaning a network of brain regions was actively holding onto information even when no processing was called for. Such information about the scope and timing of brain activation allows Newman to associate specific brain regions with specific cognitive processes.
In an earlier experiment testing verbal reasoning and working memory, Newman discovered additional evidence of differentiated brain activity. Subjects were given brain teasers based on the riddle "Brothers and sisters have I none. That man's father is my father's son. Who is in the photograph?" The riddles were presented in two parts, so Newman could better track when and where brain activity cranked up. The results, she says, demonstrate the human brain's tag-team approach to problem-solving.
"When we presented the first half of the riddle, there wasn't much processing to be done. Then we presented the second part, and the brain had to pull the first phrase out of working memory to incorporate it," she says. "For the easier riddles, the prefrontal cortex [a brain region connected with short-term memory] hung back, mostly uninvolved. But when the riddle was really hard, the prefrontal cortex would jump in and help out. We saw this in the time courses--as soon as the subject hit a mental stumbling block and the computational demand was high, the prefrontal cortex activation went up."
In other words, brain regions form dynamic networks, says Newman, with different regions being "recruited" as they are needed.
Left, right, center?
Greater understanding of how and when brain networks function could translate into important clinical applications, dramatically changing treatments for disorders such as Alzheimer's or schizophrenia. Newman is especially interested in tackling reading disorders.
"When I was young, I was in remedial reading at school," says Newman, now an assistant professor of psychology. "I had serious problems sounding out words, I couldn't do phonics. So I found another way. I learned to read by memorizing."
Today, having pushed herself to "get around the problem," Newman is planning to explore how adult dyslexics read. What brain regions do they use when they're performing a reading task? Are they the same regions as a normal population?
"Typically, adult dyslexics do learn to read," she says, "but how are they reading? What kinds of strategies do they use? Maybe we can find ways to help dyslexics use certain brain regions when they're performing a task or find ways to recruit a region that isn't being used. Hopefully, we can turn that knowledge into new remediations or teaching strategies that will help kids learn to read."
Newman is also planning to study how working memory functions in what she calls "normal aging." Rather than focus on age-related decline of mental faculties, Newman thinks fMRI studies could show that aging populations just use their brains differently. "The elderly have a great knowledge base to draw from," she says. "When you sit down with an older person, you find a lot of wisdom." Newman wants to find where wisdom lies.
Researchers know astonishingly little about what our brains--aged or not--actually do or how they do it, according to Newman. Many studies have been conducted on the brain's left hemisphere, largely because it contains the language and logic centers of the brain, Newman says, and as a result, there a lot of theories and hypotheses about what's going on in the left brain. But not so for the right hemisphere.
The brain's mysterious right half is another of Newman's research interests. In her problem-solving studies, she has seen the right hemisphere become actively involved in planning as well as evidence that in problem-solving, its function is distinct from that of the left. "But figuring out what it is doing, what it is contributing, is difficult," she says. "There's a whole hemisphere there to figure out."
The mind moves on
Some critics question whether fMRI work can measure brain function at all, let alone determine what the right hemisphere does or where wisdom resides. Newman explains that there is about a six-second delay between when brain neurons fire and when the hemodynamic "brain blush" peaks, so what fMRI measures is actually a swift but secondary response. Critics argue that the brief lag means fMRI cannot be said to truly measure neural functioning.
The six-second delay isn't going away, but Newman says a growing body of research supports a strong correlation between neural firing and hemodynamic response. Also, she points out, brain imaging using fMRI technology is a very new field, not yet 20 years old, so the technology and researchers' expertise in using it are still developing rapidly.
Another question raised by fMRI research is harder to answer. If fMRI machines capture our brains at work, do they also read our minds?
We differentiate brain and mind clearly in human language: we keep someone "in mind" or "on our mind," not brain; we are "open-minded" and "mindful" (or mindless). We have a "mindset," a "mind's eye." We use "mind" to mean human thought and consciousness, distinguishing it from the physical brain.
Newman makes the distinction too. "You have the physical reality of the brain, neurons that are connected to each other. The biology of it is just the biology. The mind is what makes the biology work," she says. "To me, the mind is who we are. When you die, you leave behind the biological shell. The brain stays behind, the mind moves on."
But brain and mind are deeply connected too, Newman insists. Damage to parts of the brain, for example, makes some mental tasks impossible, as anyone familiar with Alzheimer's or brain tumor patients knows. "Certain parts of the brain are unique to certain cognitive processes, and if that part is damaged or gone, you can not perform certain tasks. So there is a relationship there," she says.
What kind of relationship? "I'm not sure," Newman answers. "But I see my work as trying to figure out what that relationship is, the relationship between mind and brain."
By the way, the answer is Friday.
Lauren J. Bryant is editor of Research & Creative Activity magazine.