Matthew Elliott: Modeling Networks

Matthew Elliott is Caltech's newest assistant professor of economics. Born in England, he earned his BA and MPhil from Oxford in 2002 and 2004. After receiving his PhD from Stanford in 2011, he spent a year at Microsoft Research in Cambridge, Massachusetts, before arriving in Pasadena this fall.

Elliott's research focuses on mathematically modeling different kinds of networks. For example, in networked markets, the interactions among players are constrained in a way that can be represented as a network. In a labor market, for instance, not everyone can be employed in every job, whether it's because they're not qualified, they don't have the requisite connections to get the job, or they simply aren't aware that there's an opening. Elliott distills this kind of complex system into its mathematical essence, developing theories that can eventually inform policy. His research is part of the Social and Information Science Laboratory, which is funded by the Gordon and Betty Moore Foundation and the Ronald and Maxine Linde Institute for Economic and Management Sciences. He recently spoke a little more about his work.

What's another example of a network market that you're trying to model?

Within this context of network markets, another thing you might think about is the production and sale of natural gas. The producer of natural gas can only sell its gas to another country if there's a pipeline between it and that other country. You can view the pipelines as a network that describes which countries can trade directly with which other countries. And a question you might be interested in is whether the network is built efficiently. Are there good incentives in place? What kind of inefficiencies would you expect and how bad can they be?

Does this analysis occur after the fact, or do you do this before you actually build the gas pipelines?

Most of the analysis is after the fact, and you're trying to explain what's going on. But by being able to explain things that have happened before, and why, you can hopefully understand a little better the problems that will arise in the future and try to avoid some of those inefficiencies.

What excites you most about your job?

I love doing what I do. It's the problem solving. You go to work and your job consists of playing with problems and trying to find solutions to them. I find it pretty remarkable that people pay me to do this—and it's not something I just do in my spare time.

Your research is very theoretical. But do you also work with real-world, empirical data? Or do you pass along your theories to someone else who can apply them?

Somewhere in between. A good example is a project on financial networks that I'm now working on with [Stanford economist and former Caltech professor] Matt Jackson and [MIT postdoc and Caltech graduate (BS '07)] Ben Golub. The idea is to model the network of financial relationships between either banks or countries and to understand the dependencies between them. What we want to know is, if one of those countries or banks receives some shock that's going to cause it to fail, how does that spread through the system? When does one failure lead to a contagion of other failures?

Sounds like something that's quite relevant today.

It's definitely a topical thing, and we're certainly not the only people working on this. A small part of that project is collecting data on European countries and their cross holdings. Then we try to see what our theory has to say when we apply it to the data.

I'm very aware that the research I do is very theoretical, and most of the time it isn't going to specifically be something that policymakers are going to read and take to heart. But I think my work does provide a framework for them to think about problems. I think it's exciting to be able to do that.

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Marcus Woo
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Ready for Your Close-Up?

Caltech study shows that the distance at which facial photos are taken influences perception

PASADENA, Calif.—As the saying goes, "A picture is worth a thousand words." For people in certain professions—acting, modeling, and even politics—this phrase rings particularly true. Previous studies have examined how our social judgments of pictures of people are influenced by factors such as whether the person is smiling or frowning, but until now one factor has never been investigated: the distance between the photographer and the subject. According to a new study by researchers at the California Institute of Technology (Caltech), this turns out to make a difference—close-up photo subjects, the study found, are judged to look less trustworthy, less competent, and less attractive.

The new finding is described in this week's issue of the open-access journal PLoS One.

Pietro Perona, the Allen E. Puckett Professor of Electrical Engineering at Caltech, came up with the initial idea for the study. Perona, an art history enthusiast, suspected that Renaissance portrait paintings often featured subtle geometric warping of faces to make the viewer feel closer or more distant to a subject. Perona wondered if the same sort of warping might affect photographic portraits—with a similar effect on their viewers—so he collaborated with Ralph Adolphs, Bren Professor of Psychology and Neuroscience and professor of biology, and CNS graduate student Ronnie Bryan (PhD '12) to gather opinions on 36 photographs representing two different images of 18 individuals. One of each pair of images was taken at close range and the second at a distance of about seven feet.

"It turns out that faces photographed quite close-up are geometrically warped, compared to photos taken at a larger distance," explains Bryan. "Of course, the close picture would also normally be larger, higher resolution and have different lighting—but we controlled for all of that in our study. What you're left with is a warping effect that is so subtle that nobody in our study actually noticed it. Nonetheless, it's a perceptual clue that influenced their judgments."

That subtle distance warping, however, had a big effect: close-up photos made people look less trustworthy, according to study participants. The close-up photo subjects were also judged to look less attractive and competent.

"This was a surprising, and surprisingly reliable, effect," says Adolphs. "We went through a bunch of experiments, some testing people in the lab, and some even over the Internet; we asked participants to rate trustworthiness of faces, and in some experiments we asked them to invest real money in unfamiliar people whose faces they saw as a direct measure of how much they trusted them."

Across all of the studies, the researchers saw the same effect, Adolphs says: in photos taken from a distance of around two feet, a person looked untrustworthy, compared to photos taken seven feet away. These two distances were chosen by the researchers because one is within, and the other outside of, personal space—which on average is about three to four feet from the body.

In some of the studies, the researchers digitally warped images of faces taken at a distance to artificially manipulate how trustworthy they would appear. "Once you know the relation between the distance warp and the trustworthiness judgment, you could manipulate photos of faces and change the perceived trustworthiness,'' notes Perona.

He says that the group is now planning to build on these findings, using machine-vision techniques—technologies that can automatically analyze data in images. For example, one application would be for a computer program to have the ability to evaluate any face image in a magazine or on the Internet and to estimate the distance at which the photo was taken.

"The work might also allow us to estimate the perceived trustworthiness of a particular face image," says Perona. "You could imagine that many people would be interested in such applications—particularly in the political arena."

The study, "Perspective Distortion from Interpersonal Distance Is an Implicit Visual Cue for Social Judgments of Faces," was funded by grants from the National Institute of Mental Health and from the Gordon and Betty Moore Foundation.

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Katie Neith
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When Judging Portraits, Distance Matters
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Making the Healthy Choice

Caltech-led scientists find that competition between two brain regions influences the ability to make healthy choices

PASADENA, Calif.—Almost everyone knows the feeling: you see a delicious piece of chocolate cake on the table, but as you grab your fork, you think twice. The cake is too fattening and unhealthy, you tell yourself. Maybe you should skip dessert.

But the cake still beckons.

In order to make the healthy choice, we often have to engage in this kind of internal struggle. Now, scientists at the California Institute of Technology (Caltech) have identified the neural processes at work during such self-regulation—and what determines whether you eat the cake.

"We seem to have independent systems capable of guiding our decisions, and in situations like this one, these systems may compete for control of what we do," says Cendri Hutcherson, a Caltech postdoctoral scholar who is the lead author on a new paper about these competing brain systems, which will be published in the September 26 issue of the Journal of Neuroscience.

"In many cases, these systems guide behavior in the same direction, so there's no conflict between them," she adds. "But in other cases, like the all-too-common inner fight to resist the temptation of eating the chocolate cake, they can guide behavior toward different outcomes. Furthermore, the outcome of the decision seems to depend on which of the two systems takes control of behavior."

A large body of evidence shows that people make decisions by assigning different values to the various options, says Antonio Rangel, a professor of economics and neuroscience and the senior author of the paper. To make their decisions, people select the choice with the highest value. "An important and controversial open question—which this study was designed to address—is whether there is a single value signal in the brain, or if there are instead multiple value signals with different properties that compete for the control of behavior."

According to the single-value hypothesis, Rangel explains, the ability to say no to the chocolate cake depends on just one system that compares values like healthiness and taste. But the multiple-value hypothesis suggests that there are different systems that process different values. The ability to turn down the cake therefore depends on whether the brain can activate the appropriate system—the one that evaluates healthiness. If you do not want the cake, it means you place a higher value on health than on taste and your brain acts accordingly.

In the study, the researchers asked 26 volunteers to refrain from eating for four hours prior to being tested. During the experiment, a functional magnetic resonance imaging (fMRI) machine was used to measure the brain activity of the hungry participants while they decided how much they were willing to pay for different snacks, which were shown on a computer screen. The items, including foods like chips and vegetables, varied in taste and healthiness. The subjects were explicitly asked to make their choices in one of three conditions: while attempting to suppress their desire to eat the food, while attempting to increase their desire to eat the food, or while acting normally. The volunteers could do whatever they wanted to control themselves—for example, focusing on the taste (say, to increase their desire to eat something delicious but unhealthy) or the healthiness of the item (to reduce that urge).

After a four-second period, the participants placed real bids for the right to buy the items that reflected the value they placed on the food.

The researchers found that activity in two different brain areas correlated with how much the participants said they wanted an item, as indicated by their bids. The two regions were the dorsolateral prefrontal cortex (dlPFC), which sits behind the temples, and the ventromedial prefrontal cortex (vmPFC), which is in the middle of the forehead just above the eyes.

Significantly, the two areas played very different roles in the self-regulation process. When volunteers told themselves not to want the food, the dlPFC seemed to take control; there was a stronger correlation between the signals in this area and behavior, while the signals in the vmPFC appeared to have no influence on behavior. When the volunteers encouraged themselves to want the food, however, the role of each brain region flipped. The vmPFC took control while the signals in the dlPFC appeared to have no effect.

The researchers also found that the brain's ability to switch control between these two areas was not instantaneous. It took a couple of seconds before the brain was able to fully ignore the conflicting region. For example, when a volunteer tried to suppress a craving, the vmPFC initially appeared to drive behavior. Only after a couple of seconds—while the participant tried to rein in his or her appetite—did the correlation between bids and vmPFC activity disappear and the dlPFC seem to take over.

"This research suggests a reason why it feels so difficult to control your behavior," Hutcherson says. "You've got these really fast signals that say, go for the tempting food. But only after you start to go for it are you able to catch yourself and say, no, I don't want this."

Previous work in Rangel's lab showed that when dieters made similar food choices, their decisions were controlled only by the vmPFC. The researchers speculate that because dieters are more accustomed to self-control, their brains do not show the neural struggle seen in the new study. If that is the case, then it may be possible that people can improve their self-control with more practice. 

In addition to Hutcherson and Rangel, the other authors on the Journal of Neuroscience paper are Hilke Plassmann from the École Normale Supérieure in France and James Gross of Stanford. The title of the paper is "Cognitive regulation during decision making shifts behavioral control between ventromedial and dorsolateral prefrontal value systems." This research was funded by grants from the National Science Foundation, the National Institutes of Health, and the Gordon and Betty Moore Foundation.

 

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Caltech and Princeton University Press Release Thirteenth Volume of Einstein Papers

In the fall of 1922, when Albert Einstein's Nobel Prize in Physics was announced, the already-famous physicist was on a steamer headed for Japan. The detailed and poetic travel diary he kept during his journey to Japan, Palestine, and Spain is among the documents included in the latest volume in the Einstein Papers ProjectThe Collected Papers of Albert Einstein: Volume 13: The Berlin Years: Writings & Correspondence, January 1922–March 1923 (Documentary Edition), which will be released September 25. 

The volume covers a turbulent 15 months in Einstein's life and includes several hundred previously unpublished and unknown articles and letters, some of which express his desire for "a normal life." The scientist's writings convey a feeling of restlessness and a strong desire to escape the demands of his increased fame and heightened visibility. His diary entries paint a vivid picture of an Einstein who, fearful for his safety following the assassination of his friend the German foreign minister Walter Rathenau, decided to leave his home in Berlin and contemplated leaving academic life entirely, but who thoroughly enjoyed the sights and peoples he encountered for the first time on his six-month long voyage.

"This latest volume is extraordinarily rich, and illuminates in great detail Einstein's scientific work and his exchanges and collaboration with many scientists in Europe, Japan, and the U.S.," says Diana Kormos-Buchwald, the general editor of the series, a professor of history at Caltech, and the director of the Einstein Papers Project. "Most striking is seeing Einstein so thoroughly engaged in numerous professional and political activities while in private worrying about his own safety, given the rather violent atmosphere in Berlin at the time."

The volume contains 36 scientific writings by Einstein, including a paper written with Paul Ehrenfest, which anticipates the quantum measurement problem. During this time, Einstein also began investigating the possibilities and restrictions that relativity implied for a unified field theory of the gravitational and electromagnetic fields.

Published beginning in 1987, the first 12 volumes of The Collected Papers cover Einstein's life beginning with his early years up until his 44th birthday. By series' completion, The Collected Papers will comprise nearly 30 volumes and will contain more than 14,000 documents. Sponsored by the Hebrew University of Jerusalem and Princeton University Press, the project is located at and supported by Caltech.      

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Kimm Fesenmaier
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13<sup>th</sup> Volume of Einstein's Papers Published
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NIMH Awards $9 Million Grant to Caltech Researchers

PASADENA, Calif.—The National Institute of Mental Health has awarded a five-year, $9 million grant to a research group at the California Institute of Technology (Caltech) to study the neurobiology of social decision making.

The grant establishes a Silvio O. Conte Center for Neuroscience Research at Caltech, where researchers will use electrophysiology and functional magnetic resonance imaging to investigate how humans make social decisions. The grant will support the operation of research equipment, the hiring of students and postdoctoral scholars, and the formation of a new collaborative research group.

Social decision making, in contrast to individual decision making, revolves around situations where subjects are exposed to concepts such as altruism, cooperation, punishment, and retribution. It involves learning how to make decisions by watching other people, making decisions that benefit other people, and cooperating with others to achieve a common goal. Caltech researchers will investigate how social decision making occurs at the most fundamental level in the human brain.

Ralph Adolphs, Bren Professor of Psychology and Neuroscience, will direct the center. Principal investigators will be Richard Andersen, the James G. Boswell Professor of Neuroscience; John O'Doherty, professor of psychology; and Antonio Rangel, professor of economics and neuroscience.

"This award acknowledges that basic research is of critical importance to understanding psychiatric illnesses," says Adolphs. "A large number of decisions in everyday life occur in a social context, and this breaks down in diseases ranging from autism to schizophrenia to mood disorders."

Researchers in the new center will rely on two core Caltech resources for their investigations: the Psychological Assessment Lab, led by senior research scientist Lynn Paul, for recruiting and assessing human subjects, and the Caltech Brain Imaging Center, headed by Mike Tyszka, who is a member of the professional staff.

According to Adolphs, the team has already begun planning studies to investigate the neural circuits underlying simple choices, how we learn to make good choices from other people, and how we make decisions that benefit others. 

The principal investigators are collaborating closely with several other faculty at Caltech, including Doris Tsao (assistant professor of biology), Colin Camerer (Robert Kirby Professor of Behavioral Economics), Peter Bossaerts (William D. Hacker Professor of Economics and Management and professor of finance), and Shinsuke Shimojo (Gertrude Baltimore Professor of Experimental Psychology). The Caltech group also will collaborate with investigators nationally and internationally.

Named in memory of Massachusetts Rep. Silvio O. Conte, the NIMH's Conte Centers bring together diverse expertise and cutting-edge technology to gain new knowledge about mental-health disorders with the goal of improving diagnosis and treatment.

More information is available at the Conte Center's website: conte.caltech.edu.

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Brian Bell
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Thinking and Choosing in the Brain

Caltech researchers study over 300 lesion patients

PASADENA, Calif.—The frontal lobes are the largest part of the human brain, and thought to be the part that expanded most during human evolution. Damage to the frontal lobes—which are located just behind and above the eyes—can result in profound impairments in higher-level reasoning and decision making. To find out more about what different parts of the frontal lobes do, neuroscientists at the California Institute of Technology (Caltech) recently teamed up with researchers at the world's largest registry of brain-lesion patients. By mapping the brain lesions of these patients, the team was able to show that reasoning and behavioral control are dependent on different regions of the frontal lobe than the areas called upon when making a decision.

Their findings are described online this week in the early edition of the Proceedings of the National Academy of Sciences (PNAS).

The team analyzed data that had been acquired over a 30-plus-year time span by scientists from the University of Iowa's department of neurology—which has the world's largest lesion patient registry. They used that data to map brain activity in nearly 350 people with damage, or lesions, in their frontal lobes. The records included data on the performances of each patient while doing certain cognitive tasks.

By examining these detailed files, the researchers were able to see exactly which parts of the frontal lobes are critical for tasks like behavioral control and decision making.  The intuitive difference between these two types of processing is something we encounter in our lives all the time. Behavioral control happens when you don't order an unhealthy chocolate sundae you desire and go running instead. Decision making based on reward, on the other hand, is more like trying to win the most money in Vegas—or indeed choosing the chocolate sundae.

"These are really unique data that could not have been obtained anywhere else in the world," explains Jan Glascher, lead author of the study and a visiting associate in psychology at Caltech. "To address the question that we were interested in, we needed both a large number of patients with very well-measured lesions in the brain, and also a very thorough assessment of their reasoning and decision-making abilities across a battery of tasks."

That quantification of the lesions as well as the different task measurements came from several decades of work led by two coauthors on the study: Hanna Damasio, Dana Dornsife Chair in Neuroscience at the University of Southern California (USC); and Daniel Tranel, professor or neurology and psychology at the University of Iowa.

"The patterns of lesions that impair specific tasks showed a very clear separation between those regions of the frontal lobes necessary for controlling behavior, and those necessary for how we give value to choices and how we make decisions," says Tranel.

Ralph Adolphs, Bren Professor of Psychology and Neuroscience at Caltech and a coauthor of the study, says that aspects of what the team found had been observed previously using fMRI methods in healthy people. But, he adds, those previous studies only showed which parts of the brain are activated when people think or choose, but not which are the most critical areas, and which are less important. 

"Only lesion mapping, like we did in the present study, can show you which parts of the brain are actually necessary for a particular task," he says. "This information is crucial, not only for basic cognitive neuroscience, but also for linking these findings to clinical relevance." 

For example, several different parts of the brain might be activated when you are making a particular type of decision, explains Adolphs. If there is a lesion in one of these areas, the rest of your brain might be able to compensate, leaving little or no impairment. But if a lesion occurs in another area, you might wind up with a lifelong disability in decision making. Knowing which lesion leads to which outcome is something only this kind of detailed lesion study can provide, he says.

"That knowledge will be tremendously useful for prognosis after brain injury," says Adolphs. "Many people suffer injury to their frontal lobes—for instance, after a head injury during an automobile accident—but the precise pattern of the damage will determine their eventual impairment."

According to Tranel, the team is already working on their next project, which will use lesion mapping to look at how damage to particular brain regions can impact mood and personality. " There are so many other aspects of human behavior, cognition, and emotion to investigate here, that we've barely begun to scratch the surface," he says.

Other collaborators on the PNAS paper, "Lesion Mapping of Cognitive Control and Value-based Decision-making in the Prefrontal Cortex," were Lynn Paul, a senior research scientist at Caltech; David Rudrauf and Matt Calamia from the University of Iowa; and Antoine Bechara from USC. The study was supported by grants from the German Ministry of Research and Education, the National Institutes of Health, the Kiwanis Foundation, and the Gordon and Betty Moore Foundation.

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Katie Neith
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Forging Ahead

Recently graduated Caltech senior rekindles childhood passions

It's called Greek fire. Invented around AD 670, it was one of the first flamethrowers, involving a pressurized siphon to shoot a stream of liquid flame at enemies. The Byzantine Empire used this incendiary weapon to defend against fleets of Arab ships in the first and second sieges of Constantinople in 674–678 and 717–718. "It was a very fearsome naval weapon at the time," says Tom Harris, who was one of the 232 students awarded bachelor's degrees from Caltech last week.

But historical details of the weapon—how it was invented and how it worked—are murky. That mystery made Greek fire a perfect thesis topic for Harris, who graduated with a double major in history and mechanical engineering. Working with Warren Brown, a professor of history at Caltech, Harris spent much of his senior year studying Greek fire and analyzing how it worked based on original historical documents and our modern-day understanding of fluid mechanics. He also consulted with Joe Shepherd, the C. L. Kelly Johnson Professor of Aeronautics and professor of mechanical engineering, and Tim Colonius, a professor of mechanical engineering.

His conclusions? "Greek fire was an impressive weapon, but it wasn't that effective in the naval warfare that was practiced at the time," Harris says. Although he points out that his analysis is far from definitive, he made some calculations using a simple model of how Greek fire might have worked, and found that the weapon could shoot fire as far as about 50 meters—which is not enough distance to devastate a foe in a naval battle. "A lot of people in the past have hypothesized that this device did not have a very long range, and that's why it wasn't really effective," Harris explains. "My analysis seems to corroborate that."

Harris came to Caltech with an undeclared major, thinking he would study computer science. But, having been an avid Lego builder as a kid, he was drawn to mechanical engineering. He also has an interest in medieval history, which similarly dates back to his childhood—he loved pirates and knights, and both his parents were history majors—and after he took Brown's medieval history class, his impression of the study of history changed. Instead of reading textbooks and analysis from other historians, Harris and his dozen or so classmates read and analyzed original documents.

A sampling of Harris's pieces.
Credit: Tom Harris

After his sophomore year, Harris spent a month in Rome learning about structural engineering as part of a UC Davis program. He took advantage of his time in Europe by pursuing yet another childhood passion: swords. After the program ended, he stayed in Italy for another week, taking blacksmithing lessons in Le Marche, and he then went to England for another week of lessons. He made various pieces, including metal leaves, a fire poker, and scrollwork similar to the old metal handrails you can see around Caltech's campus. In England, he forged a short sword called a seax.

The following spring break, Harris once again traveled to England, to learn swordmaking. During his free time, he spent hours at the British Museum looking at swords and other medieval weaponry.

Returning to campus, Harris discovered that other Techers were interested in blacksmithing, and so—with the help of the George W. Housner Student Discovery Fund—he led an effort to get a blacksmithing forge for the student shop on campus. The forge hasn't arrived yet, but when it does, Ben Abbott, an electrical engineer with the LIGO project and a blacksmith with more than two decades' worth of experience, has volunteered to teach students the art and craft of blacksmithing.

For Harris, blacksmithing—and Caltech—allowed him to rekindle many of his childhood passions. "You could say this experience was about rediscovering my inner child and finding a more mature way of exploring these interests," he says.

Now that he's graduated, Harris will work as a quality engineer at Covidien, a company that specializes in biomedical devices, such as stents used to unblock arteries. Although he has no experience in biomedicine, he's looking forward to learning new things—something he's gotten used to at Caltech.

"Caltech has been a place where I could feed my desire to learn," Harris says. "I'm glad for the experience I've had here."

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Marcus Woo
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L.A. Times Shines Spotlight on HSS

Caltech's core curriculum is designed to prepare students for the interdisciplinary nature of contemporary research in science and technology. As might be expected, it requires that students become well versed in mathematics and the sciences. What might come as a surprise to some is that Caltech's underclassmen are also required to complete what amounts to a class each quarter in the Division of the Humanities and Social Sciences (HSS)—and have been since the 1920s.

Last week, the Los Angeles Times turned the spotlight on this aspect of the Caltech experience, featuring several of the division's students, including Christina Kondos—the only member of this year's graduating class who majored in the humanities or social sciences without double-majoring in science, math, or engineering.

HSS division chair Jonathan Katz told the L.A. Times about the role the humanities and social sciences play in developing well-rounded scientists and engineers. "The goal is to produce science and engineering leaders," he said. "How can you lead if you can't communicate and don't understand the world? Students have to know how to write, how to communicate and be able to deal with the bigger populations."

The complete L.A. Times article, "Humanities have a place, even at Caltech," can be read online. 

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Kimm Fesenmaier
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The Path Less Traveled

Senior uses Caltech as the stepping-stone for a global education

Growing up, Katie Brennan didn't have a lot of opportunities to travel. So when she started her biology studies at Caltech, one of her main goals was to explore the world. Thanks to a plenitude of funding from the Institute, Brennan—a graduating senior—can now cross two more continents and the mountains of Washington State off her list.

Starting out small the summer after her freshman year, Brennan traveled to Detroit's Wayne State University, near her hometown of Grosse Pointe, for a SURF project. There, she did research in bioinformatics to help develop tools for analyzing the structure of RNA. Before returning to sunny SoCal, she attended a weeklong retreat, deep in the woods of Washington State, as a recipient of the annual Don Shepard Essay Contest, which awards funding for "a program of self-enrichment outside of science."

"I had a friend who took sky diving lessons, and another one built his own guitar. I went to a retreat center in the mountains," says Brennan, who had to take two planes, a bus, a ferry, and another bus to reach the old mining town of Holden, where the center was located. "I went hiking. I learned how to do pottery. There were deer eating outside of my door. It was really great."

For the summer between her sophomore and junior years, she applied for and won the Caltech Y's Studenski Award, which provides funding for students to travel and explore an area outside of academics. Brennan chose to go to Malawi to volunteer with Project Peanut Butter (PPB), a nonprofit organization focused on pediatric-malnutrition clinic work and research.

"Their aim is to end malnutrition, and they have developed a special kind of peanut butter that can help children recover from malnutrition very quickly," says Brennan, who spent a month and a half working in the clinic. "And once they've recovered, they are less likely to relapse into malnutrition. It's very impressive what the organization does."

In fact, Brennan was so impressed that she returned to Malawi this past summer to work on a PPB research project. This time, she was funded by the George W. Housner Student Discovery Fund, which provides support for independent study, including travel. 

Back in Africa, she worked on a study that looked at a correlation between environmental enteropathy—or intestinal infections linked to environmental factors—and malnutrition, spending three months in the impoverished nation of Malawi. It is not uncommon for families there with multiple children to have some kids who are malnourished and others that are not, so the study enrolled sets of young twins to compare individuals with similar genetic backgrounds and living environments. "It was fun because I got to work with hundreds of twins, and they were all so adorable," says Brennan.

Determined not to let her senior year go by without more travel, Brennan studied abroad at University College London for her first term. There, she had the ability to break away from biology courses and take a class in archaeology called Ancient Egypt in London.

"Our classes were taught in the British Museum, and we would have lectures in the Egyptian Gallery, which was a hugely unique experience," says Brennan, who also visited Paris, Oxford, and Dublin during her semester in Europe. "One of the biggest Egypt artifact museums in the world—the Petrie Museum—is actually on the UCL campus, so we also had class there, which was really great."

When she's not taking part in global excursions, Brennan is very active in both house activities and campus life—she is a member of both Blacker and Dabney houses, and was co-class president of the senior class this year. For the past three years, she has also been involved with a local charity called Elizabeth House that provides shelter for homeless pregnant women. What started as a volunteer commitment led to a part-time job and a possible career path: Brennan is hoping to work in development after graduation to fundraise for nonprofits. 

Her parting advice for new students is to apply for all the funds that Caltech has available. "There are so many!" she says. "They have funding for parties, for house life, for travel, for international research, all which really help you make the most of your experience here and away from campus."

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Katie Neith
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Hands-On Research

Caltech Neuroscientists Show How Brain Responds to Sensual Caress

PASADENA, Calif.—A nuzzle of the neck, a stroke of the wrist, a brush of the knee—these caresses often signal a loving touch, but can also feel highly aversive, depending on who is delivering the touch, and to whom. Interested in how the brain makes connections between touch and emotion, neuroscientists at the California Institute of Technology (Caltech) have discovered that the association begins in the brain's primary somatosensory cortex, a region that, until now, was thought only to respond to basic touch, not to its emotional quality.

The new finding is described in this week's issue of the Proceedings of the National Academy of Sciences (PNAS).

The team measured brain activation while self-identified heterosexual male subjects lay in a functional MRI scanner and were each caressed on the leg under two different conditions. In the first condition, they saw a video of an attractive female bending down to caress them; in the second, they saw a video of a masculine man doing the same thing. The men reported the experience as pleasurable when they thought the touch came from the woman, and aversive when they thought it came from the man. And their brains backed them up: this difference in experience was reflected in the activity measured in each man's primary somatosensory cortex.

"We demonstrated for the first time that the primary somatosensory cortex—the brain region encoding basic touch properties such as how rough or smooth an object is—also is sensitive to the social meaning of a touch," explains Michael Spezio, a visiting associate at Caltech who is also an assistant professor of psychology at Scripps College in Claremont, California. "It was generally thought that there are separate brain pathways for how we process the physical aspects of touch on the skin and for how we interpret that touch emotionally—that is, whether we feel it as pleasant, unpleasant, desired, or repulsive. Our study shows that, to the contrary, emotion is involved at the primary stages of social touch."

Unbeknownst to the subjects, the actual touches on their leg were always exactly the same—and always from a woman. Yet, it felt different to them when they believed a man versus a woman was doing the touching.

"The primary somatosensory cortex responded more to the 'female' touch than to the 'male' touch condition, even while subjects were only viewing a video showing a person approach their leg," says Ralph Adolphs, Bren Professor of Psychology and Neuroscience at Caltech and director of the Caltech Brain Imaging Center, where the research was done. "We see responses in a part of the brain thought to process only basic touch that were elicited entirely by the emotional significance of social touch prior to the touch itself, simply in anticipation of the caress that our participants would receive."

The study was carried out in collaboration with the husband-and-wife team of Valeria Gazzola and Christian Keysers, who were visiting Caltech from the University of Groningen in the Netherlands. 

"Intuitively, we all believe that when we are touched by someone, we first objectively perceive the physical properties of the touch—its speed, its gentleness, the roughness of the skin," says Gazzola. "Only thereafter, in a separable second step based on who touched us, do we believe we value this touch more or less."

The experiment showed that this two-step vision is incorrect, at least in terms of separation between brain regions, she says, and who we believe is touching us distorts even the supposedly objective representation of what the touch was like on the skin.

"Nothing in our brain is truly objective," adds Keysers. "Our perception is deeply and pervasively shaped by how we feel about the things we perceive." 

One possible practical implication of the work is to help reshape social responses to touch in people with autism.

"Now that we have clear evidence that primary somatosensory cortex encodes emotional significance of touch, it may be possible to work with early sensory pathways to help children with autism respond more positively to the gentle touch of their parents and siblings," says Spezio.

The work also suggests that it may be possible to use film clips or virtual reality to reestablish positive responses to gentle touch in victims of sexual and physical abuse, and torture.

Next, the researchers hope to test whether the effect is as robust in women as in men, and in both sexes across sexual orientation. They also plan to explore how these sensory pathways might develop in infants or children.

Two other collaborators who contributed to the PNAS paper, "Primary somatosensory cortex discriminates affective significance in social touch," are Fulvia Castelli from University College London and Joset Etzel from the University of Groningen. Funding for the study included grants from the Gordon and Betty Moore Foundation, the Dutch Science Foundation, a Scripps College Faculty Research grant, and a Marie Curie Excellence Grant.

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Katie Neith
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