Brain Disorder: Anxiety

Finding a way in

by Elizabeth Dougherty |

Our perception of the world arises within the brain, based on sensory information that is sometimes ambiguous, allowing more than one interpretation. Familiar demonstrations of this point include the famous Necker cube and the “duck-rabbit” drawing (right) in which two different interpretations flip back and forth over time.

Another example is binocular rivalry, in which the two eyes are presented with different images that are perceived in alternation. Several years ago, this phenomenon caught the eye of Caroline Robertson, who is now a Harvard Fellow working in the lab of McGovern Investigator Nancy Kanwisher. Back when she was a graduate student at Cambridge University, Robertson realized that binocular rivalry might be used to probe the basis of autism, among the most mysterious of all brain disorders.

Robertson’s idea was based on the hypothesis that autism involves an imbalance between excitation and inhibition within the brain. Although widely supported by indirect evidence, this has been very difficult to test directly in human patients. Robertson realized that binocular rivalry might provide a way to perform such a test. The perceptual switches that occur during rivalry are thought to involve competition between different groups of neurons in the visual cortex, each group reinforcing its own interpretation via excitatory connections while suppressing the alternative interpretation through inhibitory connections. Thus, if the balance is altered in the brains of people with autism, the frequency of switching might also be different, providing a simple and easily measurable marker of the disease state.

To test this idea, Robertson recruited adults with and without autism, and presented them with two distinct and differently colored images in each eye. As expected, their perceptions switched back and forth between the two images, with short periods of mixed perception in between. This was true for both groups, but when she measured the timing of these switches, Robertson found that individuals with autism do indeed see the world in a measurably different way than people without the disorder. Individuals with autism cycle between the left and right images more slowly, with the intervening periods of mixed perception lasting longer than in people without autism. The more severe their autistic symptoms, as determined by a standard clinical behavioral evaluation, the greater the difference.

Robertson had found a marker for autism that is more objective than current methods that involve one person assessing the behavior of another. The measure is immediate and relies on brain activity that happens automatically, without people thinking about it. “Sensation is a very simple place to probe,” she says.

A top-down approach

When she arrived in Kanwisher’s lab, Robertson wanted to use brain imaging to probe the basis for the perceptual phenomenon that she had discovered. With Kanwisher’s encouragement, she began by repeating the behavioral experiment with a new group of subjects, to check that her previous results were not a fluke. Having confirmed that the finding was real, she then scanned the subjects using an imaging method called Magnetic Resonance Spectroscopy (MRS), in which an MRI scanner is reprogrammed to measure concentrations of neurotransmitters and other chemicals in the brain. Kanwisher had never used MRS before, but when Robertson proposed the experiment, she was happy to try it. “Nancy’s the kind of mentor who could support the idea of using a new technique and guide me to approach it rigorously,” says Robertson.

For each of her subjects, Robertson scanned their brains to measure the amounts of two key neurotransmitters, glutamate, which is the main excitatory transmitter in the brain, and GABA, which is the main source of inhibition. When she compared the brain chemistry to the behavioral results in the binocular rivalry task, she saw something intriguing and unexpected. In people without autism, the amount of GABA in the visual cortex was correlated with the strength of the suppression, consistent with the idea that GABA enables signals from one eye to inhibit those from the other eye. But surprisingly, there was no such correlation in the autistic individuals—suggesting that GABA was somehow unable to exert its normal suppressive effect. It isn’t yet clear exactly what is going wrong in the brains of these subjects, but it’s an early flag, says Robertson. “The next step is figuring out which part of the pathway is disrupted.”

A bottom-up approach

Robertson’s approach starts from the top-down, working backward from a measurable behavior to look for brain differences, but it isn’t the only way in. Another approach is to start with genes that are linked to autism in humans, and to understand how they affect neurons and brain circuits. This is the bottom-up approach of McGovern Investigator Guoping Feng, who studies a gene called Shank3 that codes for a protein that helps build synapses, the connections through which neurons send signals to each other. Several years ago Feng knocked out Shank3 in mice, and found that the mice exhibited behaviors reminiscent of human autism, including repetitive grooming, anxiety, and impaired social interaction and motor control.

These earlier studies involved a variety of different mutations that disabled the Shank3 gene. But when postdoc Yang Zhou joined Feng’s lab, he brought a new perspective. Zhou had come from a medical background and wanted to do an experiment more directly connected to human disease. So he suggested making a mouse version of a Shank3 mutation seen in human patients, and testing its effects.

Zhou’s experiment would require precise editing of the mouse Shank3 gene, previously a difficult and time-consuming task. But help was at hand, in the form of a collaboration with McGovern Investigator Feng Zhang, a pioneer in the development of genome-editing methods.

Using Zhang’s techniques, Zhou was able to generate mice with two different mutations: one that had been linked to human autism, and another that had been discovered in a few patients with schizophrenia.

The researchers found that mice with the autism-related mutation exhibited behavioral changes at a young age that paralleled behaviors seen in children with autism. They also found early changes in synapses within a brain region called the striatum. In contrast, mice with the schizophrenia-related gene appeared normal until adolescence, and then began to exhibit changes in behavior and also changes in the prefrontal cortex, a brain region that is implicated in human schizophrenia. “The consequences of the two different Shank3 mutations were quite different in certain aspects, which was very surprising to us,” says Zhou.

The fact that different mutations in just one gene can produce such different results illustrates exactly how complex these neuropsychiatric disorders can be. “Not only do we need to study different genes, but we also have to understand different mutations and which brain regions have what defects,” says Feng, who received funding from the Poitras Center for Affective Disorders research and the Simons Center for the Social Brain. Robertson and Kanwisher were also supported by the Simons Center.

Surprising plasticity

The brain alterations that lead to autism are thought to arise early in development, long before the condition is diagnosed, raising concerns that it may be difficult to reverse the effects once the damage is done. With the Shank3 knockout mice, Feng and his team were able to approach this question in a new way, asking what would happen if the missing gene were to be restored in adulthood.

To find the answer, lab members Yuan Mei and Patricia Monteiro, along with Zhou, studied another strain of mice, in which the Shank3 gene was switched off but could be reactivated at any time by adding a drug to their diet. When adult mice were tested six weeks after the gene was switched back on, they no longer showed repetitive grooming behaviors, and they also showed normal levels of social interaction with other mice, despite having grown up without a functioning Shank3 gene. Examination of their brains confirmed that many of the synaptic alterations were also rescued when the gene was restored.

Not every symptom was reversed by this treatment; even after six weeks or more of restored Shank3 expression, the mice continued to show heightened anxiety and impaired motor control. But even these deficits could be prevented if the Shank3 gene was restored earlier in life, soon after birth.

The results are encouraging because they indicate a surprising degree of brain plasticity, persisting into adulthood. If the results can be extrapolated to human patients, they suggest that even in adulthood, autism may be at least partially reversible if the right treatment can be found. “This shows us the possibility,” says Zhou. “If we could somehow put back the gene in patients who are missing it, it could help improve their life quality.”

Converging paths

Robertson and Feng are approaching the challenge of autism from different starting points, but already there are signs of convergence. Feng is finding early signs that his Shank3 mutant mice may have an altered balance of inhibitory and excitatory circuits, consistent with what Robertson and Kanwisher have found in humans.

Feng is continuing to study these mice, and he also hopes to study the effects of a similar mutation in non-human primates, whose brains and behaviors are more similar to those of humans than rodents. Robertson, meanwhile, is planning to establish a version of the binocular rivalry test in animal models, where it is possible to alter the balance between inhibition and excitation experimentally (for example, via a genetic mutation or a drug treatment). If this leads to changes in binocular rivalry, it would strongly support the link to the perceptual changes seen in humans.

One challenge, says Robertson, will be to develop new methods to measure the perceptions of mice and other animals. “The mice can’t tell us what they are seeing,” she says. “But it would also be useful in humans, because it would allow us to study young children and patients who are non-verbal.”

A multi-pronged approach

The imbalance hypothesis is a promising lead, but no single explanation is likely to encompass all of autism, according to McGovern director Bob Desimone. “Autism is a notoriously heterogeneous condition,” he explains. “We need to try multiple approaches in order to maximize the chance of success.”

McGovern researchers are doing exactly that, with projects underway that range from scanning children to developing new molecular and microscopic methods for examining brain changes in animal disease models. Although genetic studies provide some of the strongest clues, Desimone notes that there is also evidence for environmental contributions to autism and other brain disorders. “One that’s especially interesting to us is a maternal infection and inflammation, which in mice at least can affect brain development in ways we’re only beginning to understand.”

The ultimate goal, says Desimone, is to connect the dots and to understand how these diverse human risk factors affect brain function. “Ultimately, we want to know what these different pathways have in common,” he says. “Then we can come up with rational strategies for the development of new treatments.”

Newly discovered neural connections may be linked to emotional decision-making

Anne Trafton |

MIT neuroscientists have discovered connections deep within the brain that appear to form a communication pathway between areas that control emotion, decision-making, and movement. The researchers suspect that these connections, which they call striosome-dendron bouquets, may be involved in controlling how the brain makes decisions that are influenced by emotion or anxiety.

This circuit may also be one of the targets of the neural degeneration seen in Parkinson’s disease, says Ann Graybiel, an Institute Professor at MIT, member of the McGovern Institute for Brain Research, and the senior author of the study.

Graybiel and her colleagues were able to find these connections using a technique developed at MIT known as expansion microscopy, which enables scientists to expand brain tissue before imaging it. This produces much higher-resolution images than would otherwise be possible with conventional microscopes.

That technique was developed in the lab of Edward Boyden, an associate professor of biological engineering and brain and cognitive sciences at the MIT Media Lab, who is also an author of this study. Jill Crittenden, a research scientist at the McGovern Institute, is the lead author of the paper, which appears in the Proceedings of the National Academy of Sciences the week of Sept. 19.

Tracing a circuit

In this study, the researchers focused on a small region of the brain known as the striatum, which is part of the basal ganglia — a cluster of brain centers associated with habit formation, control of voluntary movement, emotion, and addiction. Malfunctions of the basal ganglia have been associated with Parkinson’s and Huntington’s diseases, as well as autism, obsessive-compulsive disorder, and Tourette’s syndrome.

Much of the striatum is uncharted territory, but Graybiel’s lab has previously identified clusters of cells there known as striosomes. She also found that these clusters receive very specific input from parts of the brain’s prefrontal cortex involved in processing emotions, and showed that this communication pathway is necessary for making decisions that require an anxiety-provoking cost-benefit analysis, such as choosing whether to take a job that pays more but forces a move away from family and friends.

Her studies also suggested that striosomes relay information to cells within a region called the substantia nigra, one of the brain’s main dopamine-producing centers. Dopamine has many functions in the brain, including roles in initiating movement and regulating mood.

To figure out how these regions might be communicating, Graybiel, Crittenden, and their colleagues used expansion microscopy to image the striosomes and discovered extensive connections between those clusters of cells and dopamine-producing cells of the substantia nigra. The dopamine-producing cells send down many tiny extensions known as dendrites that become entwined with axons that come up to meet them from the striosomes, forming a bouquet-like structure.

“With expansion microscopy, we could finally see direct connections between these cells by unraveling their unusual rope-like bundles of axons and dendrites,” Crittenden says. “What’s really exciting to us is we can see that it’s small discrete clusters of dopamine cells with bundles that are being targeted.”

Hard decisions

This finding expands the known decision-making circuit so that it encompasses the prefrontal cortex, striosomes, and a subset of dopamine-producing cells. Together, the striosomes may be acting as a gatekeeper that absorbs sensory and emotional information coming from the cortex and integrates it to produce a decision on how to react, which is initiated by the dopamine-producing cells, the researchers say.

To explore that possibility, the researchers plan to study mice in which they can selectively activate or shut down the striosome-dendron bouquet as the mice are prompted to make decisions requiring a cost-benefit analysis.

The researchers also plan to investigate whether these connections are disrupted in mouse models of Parkinson’s disease. MRI studies and postmortem analysis of brains of Parkinson’s patients have shown that death of dopamine cells in the substantia nigra is strongly correlated with the disease, but more work is needed to determine if this subset overlaps with the dopamine cells that form the striosome-dendron bouquets.

Toward a better understanding of the brain

Anne Trafton |

In 2011, about a month after joining the MIT faculty, Feng Zhang attended a talk by Harvard Medical School Professor Michael Gilmore, who studies the pathogenic bacterium Enteroccocus. The scientist mentioned that these bacteria protect themselves from viruses with DNA-cutting enzymes known as nucleases, which are part of a defense system known as CRISPR.

“I had no idea what CRISPR was but I was interested in nucleases,” Zhang says. “I went to look up CRISPR, and that’s when I realized you might be able to engineer it for use for genome editing.”

Zhang devoted himself to adapting the system to edit genes in mammalian cells and recruited new members to his nascent lab at the Broad Institute of MIT and Harvard to work with him on this project. In January 2013, they reported their success in the journal Science.

Since then, scientists in fields from medicine to plant biology have begun using CRISPR to study gene function and investigate the possibility of correcting faulty genes that cause disease. Zhang now heads a lab of 19 scientists who continue to develop the system and pursue applications of genome editing, especially in neuroscience.

“The goal is to try to make our lives better by developing new technologies and using them to understand biological systems so that we can improve our treatment of disease and our quality of life,” says Zhang, who is also a member of MIT’s McGovern Institute for Brain Research and recently earned tenure in MIT’s Departments of Biological Engineering and Brain and Cognitive Sciences.

Understanding the brain

Growing up in Des Moines, Iowa, where his parents moved from China when he was 11, Zhang had plenty of opportunities to feed his interest in science. He participated in Science Bowl competitions and took special Saturday science classes, where he got his first introduction to molecular biology. Experiments such as extracting DNA from strawberries and transforming bacteria with genes for drug resistance whetted his appetite for genetic engineering, which was further stimulated by a showing of “Jurassic Park.”

“That really caught my attention,” he recalls. “It didn’t seem that far-fetched. I guess that’s what makes it good science fiction. It kind of tantalizes your imagination.”

As a sophomore in high school, Zhang began working with Dr. John Levy in a gene therapy lab at the Iowa Methodist Medical Center in Des Moines, where he studied green fluorescent protein (GFP). Scientists had recently figured out how to adapt this naturally occurring protein to tag and image proteins inside living cells. Zhang used it to track viral proteins within infected cells to determine how the proteins assemble to form new viruses. He also worked on a project to adapt GFP for a different purpose — protecting DNA from damage induced by ultraviolet light.

At Harvard University, where he earned his undergraduate degree, Zhang majored in chemistry and physics and did research under the mentorship of Xiaowei Zhuang, a professor of chemistry and chemical biology. “I was always interested in biology but I felt that it’s important to get a solid training in chemistry and physics,” he says.

While Zhang was at Harvard, a close friend was severely affected by a psychiatric disorder. That experience made Zhang think about whether such disorders could be approached just like cancer or heart disease, if only scientists knew more about their underlying causes.

“The difference is we’re at a much earlier stage of understanding psychiatric diseases. That got me really interested in trying to understand more about how the brain works,” he says.

At Stanford University, where Zhang earned his PhD in chemistry, he worked with Karl Deisseroth, who was just starting his lab with a focus on developing new technology for studying the brain. Zhang was the second student to join the lab, and he began working on a protein called channelrhodopsin, which he and Deisseroth believed held potential for engineering mammalian cells to respond to light.

The resulting technique, known as optogenetics, has transformed biological research. Collaborating with Edward Boyden, a member of the Deisseroth lab who is now a professor at MIT, Zhang adapted channelrhodopsin so that it could be inserted into neurons and make them light-sensitive. Using this approach, neuroscientists can now selectively activate and de-activate specific neurons in the brain, allowing them to map brain circuits and investigate how disruption of those circuits causes disease.

Better gene editing

After leaving Stanford, Zhang spent a year as a junior fellow at the Harvard Society of Fellows, studying brain development with Professor Paola Arlotta and collaborating with Professor George Church. That’s when he began to focus on gene editing — a type of genetic engineering that allows researchers to selectively delete a gene or replace it with a new one.

He began with zinc finger nucleases — enzymes that can be designed to target and cut specific DNA sequences. However, these proteins turned out to be challenging to work with, in part because it is so time-consuming to design a new protein for each possible DNA target.

That led Zhang to experiment with a different type of nucleases known as transcription activator-like effector nucleases (TALENs), but these also proved laborious to work with. “Learning how to use them is a project on its own,” Zhang says.

When he heard about CRISPR in early 2011, Zhang sensed that harnessing the natural bacterial process held the potential to solve many of the challenges associated with those earlier gene-editing techniques. CRISPR includes a nuclease called Cas9, which can be guided to the correct genetic target by RNA molecules known as guide strands. For each target, scientists need only design and synthesize a new RNA guide, which is much simpler than creating new TALEN and zinc finger proteins.

Since his first CRISPR paper in 2013, Zhang’s lab has devised many enhancements to the original system, such as making the targeting more precise and preventing unintended cuts in the wrong locations. They also recently reported another type of CRISPR system based on a different nuclease called Cpf1, which is simpler and has unique features that further expand the genome editing toolbox.

Zhang’s lab has become a hub for CRISPR research worldwide. It has shared CRISPR-Cas9 components in response to nearly 30,000 requests from academic laboratories around the world and has trained thousands of researchers in the use of CRISPR-Cas9 genome-editing technology through in-person events and online opportunities.

His team is now working on creating animal models of autism, Alzheimer’s, and other neurological disorders, and in the long term, they hope to develop CRISPR for use in humans to potentially cure diseases caused by defective genes.

“There are many genetic diseases that we don’t have any way of treating and this could be one way, but we still have to do a lot of work,” Zhang says.

Neuroscientists discover a gene that controls worms’ behavioral state

Anne Trafton |

In a study of worms, MIT neuroscientists have discovered a gene that plays a critical role in controlling the switch between alternative behavioral states, which for humans include hunger and fullness, or sleep and wakefulness.

This gene, which the researchers dubbed vps-50, helps to regulate neuropeptides — tiny proteins that carry messages between neurons or from neurons to other cells. This kind of signaling is important for controlling physiology and behavior in animals, including humans. Deletions of the human counterpart of the vps-50 gene have been found in some people with autism.

“Given what is reported in this paper about how the gene works, coupled with findings by others concerning the genetics of autism, we suggest that the disruption of the function of this gene could promote autism,” says H. Robert Horvitz, the David H. Koch Professor of Biology and a member of MIT’s McGovern Institute for Brain Research.

Horvitz and Martha Constantine-Paton, an MIT professor of brain and cognitive sciences and member of the McGovern Institute, are the senior authors of the study, which appears in the March 3 issue of the journal Current Biology. The paper’s lead authors are former MIT postdocs Nicolas Paquin and Yasunobu Muruta.

Influencing behavior

Neuropeptides, which are involved in brain functions such as reward, metabolism, and learning and memory, are released from cellular structures called dense-core vesicles.

In the new study, the researchers found that the vps-50 gene encodes a protein that is important in the generation of such vesicles and in the release of neuropeptides from them.

They discovered the protein in the worm Caenorhabditis elegans, where it is found primarily in nerve cells. In those cells, vps-50 associates with both synaptic vesicles and dense-core vesicles, which release neurotransmitters such as dopamine and serotonin. The researchers showed that vps-50 is required for maturation of the dense-core vesicles and also regulates activity of a proton pump that acidifies the vesicles. Without the proper acidity level, the vesicles’ ability to produce neuropeptides is impaired.

The researchers also found distinctive behavioral effects in C. elegans worms, which normally change their speed depending on food availability and whether they have recently eaten.

“Worms are the fastest when food (bacteria) is absent, presumably because they are looking for food,” Paquin says. “When they reach food, they slow down, but when you make them hungry for 30 minutes before putting them on food, they slow down even more.”

Worms lacking vps-50 behaved as if they were hungry — moving slowly through a food-rich area even when they were well fed, the researchers found. This suggests that the worms without vps-50 are unable to signal that they are full and continue to behave as if they are hungry. The researchers also found an equivalent gene in mice and showed that it can compensate for loss of the worm version of vps-50, showing that the two genes have the same function.

Human link

One important question raised by the study is how the mouse and human versions of vps-50 affect behavior in those animals, Horvitz says. Although this study focused on switching between hunger and fullness, neuropeptide signaling has been previously shown to control other alternative behaviors such as sleep and wakefulness and also to control social behaviors, such as anxiety.

The researchers suggest that studies of vps-50 might shed light on aspects of autism, because the human version of the gene is missing in some people with autism. Furthermore, a protein known as UNC-31, which is also located in dense-core vesicles has also been linked with autism in humans and mice. When mutated in worms, UNC-31 produces behavioral effects similar to those caused by vps-50 mutations.

“For these reasons, we hope that our studies of vps-50 will provide insights into human neuropsychiatric disorders,” Horvitz says.

The research was funded by the National Institutes of Health and the Simons Center for the Social Brain at MIT.

Possible new weapon against PTSD

Anne Trafton |

About 8 million Americans suffer from nightmares and flashbacks to a traumatic event. This condition, known as post-traumatic stress disorder (PTSD), is particularly common among soldiers who have been in combat, though it can also be triggered by physical attack or natural disaster.

Studies have shown that trauma victims are more likely to develop PTSD if they have previously experienced chronic stress, and a new study from MIT may explain why. The researchers found that animals who underwent chronic stress prior to a traumatic experience engaged a distinctive brain pathway that encodes traumatic memories more strongly than in unstressed animals.

Blocking this type of memory formation may offer a new way to prevent PTSD, says Ki Goosens, the senior author of the study, which appears in the journal Biological Psychiatry.

“The idea is not to make people amnesic but to reduce the impact of the trauma in the brain by making the traumatic memory more like a ‘normal,’ unintrusive memory,” says Goosens, an assistant professor of neuroscience and investigator in MIT’s McGovern Institute for Brain Research.

The paper’s lead author is former MIT postdoc Michael Baratta.

Strong memories

Goosens’ lab has sought for several years to find out why chronic stress is so strongly linked with PTSD. “It’s a very potent risk factor, so it must have a profound change on the underlying biology of the brain,” she says.

To investigate this, the researchers focused on the amygdala, an almond-sized brain structure whose functions include encoding fearful memories. They found that in animals that developed PTSD symptoms following chronic stress and a traumatic event, serotonin promotes the process of memory consolidation. When the researchers blocked amygdala cells’ interactions with serotonin after trauma, the stressed animals did not develop PTSD symptoms. Blocking serotonin in unstressed animals after trauma had no effect.

“That was really surprising to us,” Baratta says. “It seems like stress is enabling a serotonergic memory consolidation process that is not present in an unstressed animal.”

Memory consolidation is the process by which short-term memories are converted into long-term memories and stored in the brain. Some memories are consolidated more strongly than others. For example, “flashbulb” memories, formed in response to a highly emotional experience, are usually much more vivid and easier to recall than typical memories.

Goosens and colleagues further discovered that chronic stress causes cells in the amygdala to express many more 5-HT2C receptors, which bind to serotonin. Then, when a traumatic experience occurs, this heightened sensitivity to serotonin causes the memory to be encoded more strongly, which Goosens believes contributes to the strong flashbacks that often occur in patients with PTSD.

“It’s strengthening the consolidation process so the memory that’s generated from a traumatic or fearful event is stronger than it would be if you don’t have this serotonergic consolidation engaged,” Baratta says.

“This study is a very nice dissection of the mechanism by which chronic stress seems to activate new pathways not seen in unstressed animals,” says Mireya Nadal-Vicens, medical director of the Center for Anxiety and Traumatic Stress Disorders at Massachusetts General Hospital, who was not part of the research team.

Drug intervention

This memory consolidation process can take hours to days to complete, but once a memory is consolidated, it is very difficult to erase. However, the findings suggest that it may be possible to either prevent traumatic memories from forming so strongly in the first place, or to weaken them after consolidation, using drugs that interfere with serotonin.

“The consolidation process gives us a window in which we can possibly intervene and prevent the development of PTSD. If you give a drug or intervention that can block fear memory consolidation, that’s a great way to think about treating PTSD,” Goosens says. “Such an intervention won’t cause people to forget the experience of the trauma, but they might not have the intrusive memory that is ultimately going to cause them to have nightmares or be afraid of things that are similar to the traumatic experience.”

The Food and Drug Administration has already approved a drug called agomelatine that blocks this type of serotonin receptor and is used as an antidepressant.

Such a drug might also be useful to treat patients who already suffer from PTSD. These patients’ traumatic memories are already consolidated, but some research has shown that when memories are recalled, there is a window of time during which they can be altered and reconsolidated. It may be possible to weaken these memories by using serotonin-blocking drugs to interfere with the reconsolidation process, says Goosens, who plans to begin testing that possibility in animals.

The findings also suggest that the antidepressant Prozac and other selective serotonin reuptake inhibitors (SSRIs), which are commonly given to PTSD patients, likely do not help and may actually worsen their symptoms. Prozac enhances the effects of serotonin by prolonging its exposure to brain cells. While this often helps those suffering from depression, “There’s no biological evidence to support the use of SSRIs for PTSD,” Goosens says.

“The consolidation of traumatic memories requires this serotonergic cascade and we want to block it, not enhance it,” she adds. “This study suggests we should rethink the use of SSRIs in PTSD and also be very careful about how they are used, particularly when somebody is recently traumatized and their memories are still being consolidated, or when a patient is undergoing cognitive behavior therapy where they’re recalling the memory of the trauma and the memory is going through the process of reconsolidation.”

 

How we make emotional decisions

Anne Trafton |

Some decisions arouse far more anxiety than others. Among the most anxiety-provoking are those that involve options with both positive and negative elements, such choosing to take a higher-paying job in a city far from family and friends, versus choosing to stay put with less pay.

MIT researchers have now identified a neural circuit that appears to underlie decision-making in this type of situation, which is known as approach-avoidance conflict. The findings could help researchers to discover new ways to treat psychiatric disorders that feature impaired decision-making, such as depression, schizophrenia, and borderline personality disorder.

“In order to create a treatment for these types of disorders, we need to understand how the decision-making process is working,” says Alexander Friedman, a research scientist at MIT’s McGovern Institute for Brain Research and the lead author of a paper describing the findings in the May 28 issue of Cell.

Friedman and colleagues also demonstrated the first step toward developing possible therapies for these disorders: By manipulating this circuit in rodents, they were able to transform a preference for lower-risk, lower-payoff choices to a preference for bigger payoffs despite their bigger costs.

The paper’s senior author is Ann Graybiel, an MIT Institute Professor and member of the McGovern Institute. Other authors are postdoc Daigo Homma, research scientists Leif Gibb and Ken-ichi Amemori, undergraduates Samuel Rubin and Adam Hood, and technical assistant Michael Riad.

Making hard choices

The new study grew out of an effort to figure out the role of striosomes — clusters of cells distributed through the the striatum, a large brain region involved in coordinating movement and emotion and implicated in some human disorders. Graybiel discovered striosomes many years ago, but their function had remained mysterious, in part because they are so small and deep within the brain that it is difficult to image them with functional magnetic resonance imaging (fMRI).

Previous studies from Graybiel’s lab identified regions of the brain’s prefrontal cortex that project to striosomes. These regions have been implicated in processing emotions, so the researchers suspected that this circuit might also be related to emotion.

To test this idea, the researchers studied mice as they performed five different types of behavioral tasks, including an approach-avoidance scenario. In that situation, rats running a maze had to choose between one option that included strong chocolate, which they like, and bright light, which they don’t, and an option with dimmer light but weaker chocolate.

When humans are forced to make these kinds of cost-benefit decisions, they usually experience anxiety, which influences the choices they make. “This type of task is potentially very relevant to anxiety disorders,” Gibb says. “If we could learn more about this circuitry, maybe we could help people with those disorders.”

The researchers also tested rats in four other scenarios in which the choices were easier and less fraught with anxiety.

“By comparing performance in these five tasks, we could look at cost-benefit decision-making versus other types of decision-making, allowing us to reach the conclusion that cost-benefit decision-making is unique,” Friedman says.

Using optogenetics, which allowed them to turn cortical input to the striosomes on or off by shining light on the cortical cells, the researchers found that the circuit connecting the cortex to the striosomes plays a causal role in influencing decisions in the approach-avoidance task, but none at all in other types of decision-making.

When the researchers shut off input to the striosomes from the cortex, they found that the rats began choosing the high-risk, high-reward option as much as 20 percent more often than they had previously chosen it. If the researchers stimulated input to the striosomes, the rats began choosing the high-cost, high-reward option less often.

Paul Glimcher, a professor of physiology and neuroscience at New York University, describes the study as a “masterpiece” and says he is particularly impressed by the use of a new technology, optogenetics, to solve a longstanding mystery. The study also opens up the possibility of studying striosome function in other types of decision-making, he adds.

“This cracks the 20-year puzzle that [Graybiel] wrote — what do the striosomes do?” says Glimcher, who was not part of the research team. “In 10 years we will have a much more complete picture, of which this paper is the foundational stone. She has demonstrated that we can answer this question, and answered it in one area. A lot of labs will now take this up and resolve it in other areas.”

Emotional gatekeeper

The findings suggest that the striatum, and the striosomes in particular, may act as a gatekeeper that absorbs sensory and emotional information coming from the cortex and integrates it to produce a decision on how to react, the researchers say.

That gatekeeper circuit also appears to include a part of the midbrain called the substantia nigra, which has dopamine-containing cells that play an important role in motivation and movement. The researchers believe that when activated by input from the striosomes, these substantia nigra cells produce a long-term effect on an animal or human patient’s decision-making attitudes.

“We would so like to find a way to use these findings to relieve anxiety disorder, and other disorders in which mood and emotion are affected,” Graybiel says. “That kind of work has a real priority to it.”

In addition to pursuing possible treatments for anxiety disorders, the researchers are now trying to better understand the role of the dopamine-containing substantia nigra cells in this circuit, which plays a critical role in Parkinson’s disease and may also be involved in related disorders.

The research was funded by the National Institute of Mental Health, the CHDI Foundation, the Defense Advanced Research Projects Agency, the U.S. Army Research Office, the Bachmann-Strauss Dystonia and Parkinson Foundation, and the William N. and Bernice E. Bumpus Foundation.

Genome Editing with CRISPR – Cas9

Anne Trafton |

This animation depicts the CRISPR-Cas9 method for genome editing – a powerful new technology with many applications in biomedical research, including the potential to treat human genetic disease. Feng Zhang, a leader in the development of this technology, is a faculty member at MIT, an investigator at the McGovern Institute for Brain Research, and a core member of the Broad Institute.

 

McGovern neuroscientists discover new role for ‘hunger hormone’

Anne Trafton |

About a dozen years ago, scientists discovered that a hormone called ghrelin enhances appetite. Dubbed the “hunger hormone,” ghrelin was quickly targeted by drug companies seeking treatments for obesity — none of which have yet panned out.

MIT neuroscientists have now discovered that ghrelin’s role goes far beyond controlling hunger. The researchers found that ghrelin released during chronic stress makes the brain more vulnerable to traumatic events, suggesting that it may predispose people to posttraumatic stress disorder (PTSD).

Drugs that reduce ghrelin levels, originally developed to try to combat obesity, could help protect people who are at high risk for PTSD, such as soldiers serving in war, says Ki Goosens, an assistant professor of brain and cognitive sciences at MIT, and senior author of a paper describing the findings in the Oct. 15 online edition of Molecular Psychiatry.

“Perhaps we could give people who are going to be deployed into an active combat zone a ghrelin vaccine before they go, so they will have a lower incidence of PTSD. That’s exciting because right now there’s nothing given to people to prevent PTSD,” says Goosens, who is also a member of MIT’s McGovern Institute for Brain Research.

Lead author of the paper is Retsina Meyer, a recent MIT PhD recipient. Other authors are McGovern postdoc Anthony Burgos-Robles, graduate student Elizabeth Liu, and McGovern research scientist Susana Correia.

Stress and fear

Stress is a useful response to dangerous situations because it provokes action to escape or fight back. However, when stress is chronic, it can produce anxiety, depression and other mental illnesses.

At MIT, Goosens discovered that one brain structure that is especially critical for generating fear, the amygdala, has a special response to chronic stress. The amygdala produces large amounts of growth hormone during stress, a change that seems not to occur in other brain regions.

In the new paper, Goosens and her colleagues found that the release of the growth hormone in the amygdala is controlled by ghrelin, which is produced primarily in the stomach and travels throughout the body, including the brain.

Ghrelin levels are elevated by chronic stress. In humans, this might be produced by factors such as unemployment, bullying, or loss of a family member. Ghrelin stimulates the secretion of growth hormone from the brain; the effects of growth hormone from the pituitary gland in organs such as the liver and bones have been extensively studied. However, the role of growth hormone in the brain, particularly the amygdala, is not well known.

The researchers found that when rats were given either a drug to stimulate the ghrelin receptor or gene therapy to overexpress growth hormone over a prolonged period, they became much more susceptible to fear than normal rats. Fear was measured by training all of the rats to fear an innocuous, novel tone. While all rats learned to fear the tone, the rats with prolonged increased activity of the ghrelin receptor or overexpression of growth hormone were the most fearful, assessed by how long they froze after hearing the tone. Blocking the cell receptors that interact with ghrelin or growth hormone reduced fear to normal levels in chronically stressed rats.

When rats were exposed to chronic stress over a prolonged period, their circulating ghrelin and amygdalar growth hormone levels also went up, and fearful memories were encoded more strongly. This is similar to what the researchers believe happens in people who suffer from PTSD.

“When you have people with a history of stress who encounter a traumatic event, they are more likely to develop PTSD because that history of stress has altered something about their biology. They have an excessively strong memory of the traumatic event, and that is one of the things that drives their PTSD symptoms,” Goosens says.

New drugs, new targets

Over the last century, scientists have described the hypothalamic-pituitary-adrenal (HPA) axis, which produces adrenaline, cortisol (corticosterone in rats), and other hormones that stimulate “fight or flight” behavior. Since then, stress research has focused almost exclusively on the HPA axis.

After discovering ghrelin’s role in stress, the MIT researchers suspected that ghrelin was also linked to the HPA axis. However, they were surprised to find that when the rats’ adrenal glands — the source of corticosterone, adrenaline, and noradrenaline — were removed, the animals still became overly fearful when chronically stressed. The authors also showed that repeated ghrelin-receptor stimulation did not trigger release of HPA hormones, and that blockade of the ghrelin receptor did not blunt release of HPA stress hormones. Therefore, the ghrelin-initiated stress pathway appears to act independently of the HPA axis. “That’s important because it gives us a whole new target for stress therapies,” Goosens says.

Pharmaceutical companies have developed at least a dozen possible drug compounds that interfere with ghrelin. Many of these drugs have been found safe for humans, but have not been shown to help people lose weight. The researchers believe these drugs could offer a way to vaccinate people entering stressful situations, or even to treat people who already suffer from PTSD, because ghrelin levels remain high long after the chronic stress ends.

PTSD affects about 7.7 million American adults, including soldiers and victims of crimes, accidents, or natural disasters. About 40 to 50 percent of patients recover within five years, Meyer says, but the rest never get better.

The researchers hypothesize that the persistent elevation of ghrelin following trauma exposure could be one of the factors that maintain PTSD. “So, could you immediately reverse PTSD? Maybe not, but maybe the ghrelin could get damped down and these people could go through cognitive behavioral therapy, and over time, maybe we can reverse it,” Meyer says.

Working with researchers at Massachusetts General Hospital, Goosens’ lab is now planning to study ghrelin levels in human patients suffering from anxiety and fear disorders. They are also planning a clinical trial of a drug that blocks ghrelin to see if it can prevent relapse of depression.

The research was funded by the U.S. Army Research Office, the Defense Advanced Research Projects Agency, and the National Institute of Mental Health.

Calcium reveals connections between neurons

Anne Trafton |

A team led by MIT neuroscientists has developed a way to monitor how brain cells coordinate with each other to control specific behaviors, such as initiating movement or detecting an odor.

The researchers’ new imaging technique, based on the detection of calcium ions in neurons, could help them map the brain circuits that perform such functions. It could also provide new insights into the origins of autism, obsessive-compulsive disorder and other psychiatric diseases, says Guoping Feng, senior author of a paper appearing in the Oct. 18 issue of the journal Neuron.

“To understand psychiatric disorders we need to study animal models, and to find out what’s happening in the brain when the animal is behaving abnormally,” says Feng, the James W. and Patricia Poitras Professor of Neuroscience and a member of the McGovern Institute for Brain Research at MIT. “This is a very powerful tool that will really help us understand animal models of these diseases and study how the brain functions normally and in a diseased state.”

The lead author of the Neuron paper is McGovern Institute postdoc Qian Chen.

Performing any kind of brain function requires many neurons in different parts of the brain to communicate with each other. They achieve this communication by sending electrical signals, triggering an influx of calcium ions into active cells. Using dyes that bind to calcium, researchers have imaged neural activity in neurons. However, the brain contains thousands of cell types, each with distinct functions, and the dye is taken up nonselectively by all cells, making it impossible to pinpoint calcium in specific cell types with this approach.

To overcome this, the MIT-led team created a calcium-imaging system that can be targeted to specific cell types, using a type of green fluorescent protein (GFP). Junichi Nakai of Saitama University in Japan first developed a GFP that is activated when it binds to calcium, and one of the Neuron paper authors, Loren Looger of the Howard Hughes Medical Institute, modified the protein so its signal is strong enough to use in living animals.

The MIT researchers then genetically engineered mice to express this protein in a type of neuron known as pyramidal cells, by pairing the gene with a regulatory DNA sequence that is only active in those cells. Using two-photon microscopy to image the cells at high speed and high resolution, the researchers can identify pyramidal cells that are active when the brain is performing a specific task or responding to a certain stimulus.

In this study, the team was able to pinpoint cells in the somatosensory cortex that are activated when a mouse’s whiskers are touched, and olfactory cells that respond to certain aromas.

This system could be used to study brain activity during many types of behavior, including long-term phenomena such as learning, says Matt Wachowiak, an associate professor of physiology at the University of Utah. “These mouse lines should be really useful to many different research groups who want to measure activity in different parts of the brain,” says Wachowiak, who was not involved in this research.

The researchers are now developing mice that express the calcium-sensitive proteins and also exhibit symptoms of autistic behavior and obsessive-compulsive disorder. Using these mice, the researchers plan to look for neuron firing patterns that differ from those of normal mice. This could help identify exactly what goes wrong at the cellular level, offering mechanistic insights into those diseases.

“Right now, we only know that defects in neuron-neuron communications play a key role in psychiatric disorders. We do not know the exact nature of the defects and the specific cell types involved,” Feng says. “If we knew what cell types are abnormal, we could find ways to correct abnormal firing patterns.”

The researchers also plan to combine their imaging technology with optogenetics, which enables them to use light to turn specific classes of neurons on or off. By activating specific cells and then observing the response in target cells, they will be able to precisely map brain circuits.

The research was funded by the Poitras Center for Affective Disorders Research, the National Institutes of Health and the McNair Foundation

Predicting how patients respond to therapy

Anne Trafton |

Social anxiety is usually treated with either cognitive behavioral therapy or medications. However, it is currently impossible to predict which treatment will work best for a particular patient. The team of researchers from MIT, Boston University (BU) and Massachusetts General Hospital (MGH) found that the effectiveness of therapy could be predicted by measuring patients’ brain activity as they looked at photos of faces, before the therapy sessions began.

The findings, published this week in the Archives of General Psychiatry, may help doctors more accurately choose treatments for social anxiety disorder, which is estimated to affect around 15 million people in the United States.

“Our vision is that some of these measures might direct individuals to treatments that are more likely to work for them,” says John Gabrieli, the Grover M. Hermann Professor of Brain and Cognitive Sciences at MIT, a member of the McGovern Institute for Brain Research and senior author of the paper.

Lead authors of the paper are MIT postdoc Oliver Doehrmann and Satrajit Ghosh, a research scientist in the McGovern Institute.

Choosing treatments

Sufferers of social anxiety disorder experience intense fear in social situations, interfering with their ability to function in daily life. Cognitive behavioral therapy aims to change the thought and behavior patterns that lead to anxiety. For social anxiety disorder patients, that might include learning to reverse the belief that others are watching or judging them.

The new paper is part of a larger study that MGH and BU recently ran on cognitive behavioral therapy for social anxiety, led by Mark Pollack, director of the Center for Anxiety and Traumatic Stress Disorders at MGH, and Stefan Hofmann, director of the Social Anxiety Program at BU.

“This was a chance to ask if these brain measures, taken before treatment, would be informative in ways above and beyond what physicians can measure now, and determine who would be responsive to this treatment,” Gabrieli says.

Currently doctors might choose a treatment based on factors such as ease of taking pills versus going to therapy, the possibility of drug side effects, or what the patient’s insurance will cover. “From a science perspective there’s very little evidence about which treatment is optimal for a person,” Gabrieli says.

The researchers used functional magnetic resonance imaging (fMRI) to image the brains of patients before and after treatment. There have been many imaging studies showing brain differences between healthy people and patients with neuropsychiatric disorders, but so far imaging has not been established as a way to predict patient response to particular treatments.

Measuring brain activity

In the new study, the researchers measured differences in brain activity as patients looked at images of angry or neutral faces. After 12 weeks of cognitive behavioral therapy, patients’ social anxiety levels were tested. The researchers found that patients who had shown a greater difference in activity in high-level visual processing areas during the face-response task showed the most improvement after therapy.

The findings are an important step towards improving doctors’ ability to choose the right treatment for psychiatric disorders, says Greg Siegle, associate professor of psychiatry at the University of Pittsburgh. “It’s really critical that somebody do this work, and they did it very well,” says Siegle, who was not part of the research team. “It moves the field forward, and brings psychology into more of a rigorous science, using neuroscience to distinguish between clinical cases that at first appear homogeneous.”

Gabrieli says it’s unclear why activity in brain regions involved with visual processing would be a good predictor of treatment outcome. One possibility is that patients who benefited more were those whose brains were already adept at segregating different types of experiences, Gabrieli says.

The researchers are now planning a follow-up study to investigate whether brain scans can predict differences in response between cognitive behavioral therapy and drug treatment.

“Right now, all by itself, we’re just giving somebody encouraging or discouraging news about the likely outcome” of therapy, Gabrieli says. “The really valuable thing would be if it turns out to be differentially sensitive to different treatment choices.”

The research was funded by the Poitras Center for Affective Disorders Research and the National Institute of Mental Health.