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USC scientists Arthur Toga, Paul Thompson are on the cutting edge of brain mapping

Their work straddles biological science and engineering, bringing improved measurements to clinical treatments for diseases such as Alzheimer’s and autism

Brain image
Brain image (Photo/Courtesy of USC Stevens Institute for Neuroimaging and Informatics)

Just a few decades ago, the human brain was uncharted territory. The best map — an X-ray of the soft tissue inside your skull — looked like a hovering cloud, all shadowy contours and empty space.

Paul Thompson and Arthur Toga

Professors Paul Thompson, left, and Arthur Toga and Paul Thompson lead the USC Mark and Mary Stevens Neuroimaging and Informatics Institute and its Laboratory of Neuro Imaging. (USC Photo/Gus Ruelas)

It took the advent of magnetic resonance imaging (MRI) about 30 years ago to construct the first three-dimensional pictures of the brain. Then functional MRIs (fMRI) came along and hinted at the duties of different parts of the brain – which use the most resources when you read a book, for example, or when you listen to music.

“fMRI led to some incredible insights, but the problem is, we’re always thinking and moving. This data is superimposed on all of the extraordinary things the brain already does,” said Paul Thompson of the USC Mark and Mary Stevens Neuroimaging and Informatics Institute.

“It was a little bit like looking at the city lights from an airplane,” said Thompson, professor of neurology, psychiatry and behavioral sciences, radiology, engineering and ophthalmology.

A lot of the data is, frankly, underutilized.

Arthur W. Toga

What scientists needed was a street view of the brain’s roadways, the 100 billion neurons and quadrillion connections in the human brain. fMRI and other scanning techniques produce no images, just strings of numbers that require computational algorithms to make sense.

Researchers have a lot of digital information, said Arthur Toga, Provost Professor of Ophthalmology, Neurology, Psychiatry and the Behavioral Sciences, Radiology and Engineering. “But a lot of the data is, frankly, underutilized,” he said.

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Mapping the brain

At the USC Stevens Neuroimaging and Informatics Institute, Toga and Thompson are leading mapmakers of the human brain. Their work straddles the worlds of biological science and engineering, bringing improved raw measurements to clinical treatments for diseases such as Alzheimer’s or autism. With a staff of faculty and data analysts, the institute houses a supercomputer, wet labs, a production studio and more than four petabytes of data (enough to render the special effects of a summer blockbuster movie four times over).

Harvard radiologist and leading imaging expert Bruce Rosen described Toga and Thompson’s group in the Los Angeles Times as “the world’s premier lab when it comes to finding insights about the brain in massive amounts of data from scans and genetic tests.”

Among the researchers’ projects is the ENIGMA network, a collaboration of 190 global institutions led by Thompson. The largest brain-mapping project in the world, ENIGMA – Enhancing Neuro Imaging Genetics Through Meta Analysis – enables scientists to sift out discoveries from mounds of data. “We’re all so different from each other that you need to amass a large amount of information before you can see patterns,” Thompson said.

Take ENIGMA’s work on HIV/AIDS. Researchers are beginning to understand that cocktails of HIV-fighting drugs, for all the lives they’ve saved, can’t suppress the virus in the cerebral cortex. Otherwise healthy people treated for HIV/AIDS for the last 15 to 20 years are starting to show early signs of dementia and memory loss.

Researchers need to look at HIV/AIDS patients’ brain scans to see the virus’ effects.

The ENIGMA team developed a computer program for colleagues around the world to pull relevant pieces of information from brain scans. These figures then filter to USC, where engineers take on the heavy number crunching, including cross-referencing the brain data with other medical history.

The work has yielded surprises. As the virus moves through the brain, it seems to skip over certain cells. The data shows that HIV affects mostly the motor regions of the brain – the parts that control movement – and regions less affected by other disorders such as Alzheimer’s.

Brain image

The connectome is an atlas of the roads and highways of neurons coursing through the brain. (Photo/Courtesy of USC Stevens Neuroimaging and Informatics Institute)

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Cross-border science

This border-crossing science symbolizes the possibility of collaboration that drew Toga and Thompson to USC. “We’d like to build a program that is not only an amalgamation of different disciplines, but the amalgamation of different data types across diseases, across subjects and across institutes,” Toga said. “We are going to extract more information from these various data types than has ever been done before.”

Another project from Toga and Thompson demonstrates the importance in brain mapping of the fourth dimension: time. The living brain is dynamic, and a single image might pick up a transient signal that disappears the next instant. “The brain is supposed to be adaptive – that’s how we learn. You will remember some things about this conversation, and that will change your brain,” Toga said.

Over a lifetime, some of these changes pile up. Toga and Thompson, who both hold joint appointments at the Keck School of Medicine of USC and the USC Viterbi School of Engineering, study the development of age-related diseases by visualizing how the healthy brain grows. With support from the National Institute for Mental Health, the researchers created a time-lapse arrangement of hundreds of brain scans taken from infancy to early adulthood. Toga’s daughters served as the first test subjects.

Thompson likens findings from the growth chart to being told by a pediatrician that your child is tall for her age, but underweight. “Imagine doing that for the brain,” he said.

It would seem like you need all of your brain, but you don’t.

Paul Thompson

In a landmark study in Nature, the researchers showed that the back of the brain grows rapidly in infants as senses of sight and touch develop. Growth then floods forward through parts of the brain associated with language acquisition. In the teenage years, the surge moves to the front of the brain, which is linked to decision-making and judgment.

But perhaps the biggest revelation of seeing how the brain grows wasn’t that there might be a reason teenagers make stupid mistakes. To the researchers’ surprise, they discovered that the growing brain prunes itself, cutting of whole clusters of cells. Many parts of the brain actually shrink during adolescence. “When we first ran into it in the data, we thought we’d made a blunder, all this tissue loss,” Thompson said.

That was just the beginning. Turns out, schizophrenics’ brains shed mass faster than normal. And kids with autism tend to have bigger brains; some theorize their brains don’t go through enough pruning.

“It would seem like you need all of your brain, but you don’t,” Thompson said. “Clearly not all of it is absolutely vital – there’s some redundancy. But also, clearly, you can’t do without certain critical components.”

Brain image

Each delicate line in this brain image is a thread of white matter—a chain of nerve cells surrounded by a protective layer of fat. (Photo/Courtesy of USC Stevens Neuroimaging and Informatics Institute)

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Changes over the years

At the other end of life, our brains unravel in the reverse order of development, Toga and Thompson’s research has found. Just as infants develop sensory skills first, Alzheimer’s patients don’t lose their senses of sight and touch until the very end.

“We’ve learned more about the brain in the last 25 years than in all of previous history,” Toga said. “It’s one of the most exciting times to be a neuroscientist only because the techniques have finally caught up with the complexity of the problem.”

Still, there are many things that a map of the brain might never tell us, or that we might not want to know. Toga and Thompson’s advanced imaging can reveal Alzheimer’s about a decade before symptoms appear. For now, it’s like seeing a tidal wave before it falls, Toga said, but the scans will be critical to early treatment if an Alzheimer’s cure is ever found.

Thompson holds out hope that it will happen: “With these cryptic diseases in the brain, with a little bit of investment into figuring them out, you get a real leg up in treating them.”


A version of this story was previously published in USC Trojan Family Magazine.

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USC scientists Arthur Toga, Paul Thompson are on the cutting edge of brain mapping

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