When we make complex decisions, we have to take many factors into account. Some choices have a high payoff but carry potential risks; others are lower risk but may have a lower reward associated with them.

A new study from MIT sheds light on the part of the brain that helps us make these types of decisions. The research team found a group of neurons in the brain’s striatum that encodes information about the potential outcomes of different decisions. These cells become particularly active when a behavior leads a different outcome than what was expected, which the researchers believe helps the brain adapt to changing circumstances.

“A lot of this brain activity deals with surprising outcomes, because if an outcome is expected, there’s really nothing to be learned. What we see is that there’s a strong encoding of both unexpected rewards and unexpected negative outcomes,” says Bernard Bloem, a former MIT postdoc and one of the lead authors of the new study.

Impairments in this kind of decision-making are a hallmark of many neuropsychiatric disorders, especially anxiety and depression. The new findings suggest that slight disturbances in the activity of these striatal neurons could swing the brain into making impulsive decisions or becoming paralyzed with indecision, the researchers say.

Rafiq Huda, a former MIT postdoc, is also a lead author of the paper, which appears in Nature Communications. Ann Graybiel, an MIT Institute Professor and member of MIT’s McGovern Institute for Brain Research, is the senior author of the study.

Learning from experience

The striatum, located deep within the brain, is known to play a key role in making decisions that require evaluating outcomes of a particular action. In this study, the researchers wanted to learn more about the neural basis of how the brain makes cost-benefit decisions, in which a behavior can have a mixture of positive and negative outcomes.

To study this kind of decision-making, the researchers trained mice to spin a wheel to the left or the right. With each turn, they would receive a combination of reward (sugary water) and negative outcome (a small puff of air). As the mice performed the task, they learned to maximize the delivery of rewards and to minimize the delivery of air puffs. However, over hundreds of trials, the researchers frequently changed the probabilities of getting the reward or the puff of air, so the mice would need to adjust their behavior.

As the mice learned to make these adjustments, the researchers recorded the activity of neurons in the striatum. They had expected to find neuronal activity that reflects which actions are good and need to be repeated, or bad and that need to be avoided. While some neurons did this, the researchers also found, to their surprise, that many neurons encoded details about the relationship between the actions and both types of outcomes.

The researchers found that these neurons responded more strongly when a behavior resulted in an unexpected outcome, that is, when turning the wheel in one direction produced the opposite outcome as it had in previous trials. These “error signals” for reward and penalty seem to help the brain figure out that it’s time to change tactics.

Most of the neurons that encode these error signals are found in the striosomes — clusters of neurons located in the striatum. Previous work has shown that striosomes send information to many other parts of the brain, including dopamine-producing regions and regions involved in planning movement.

“The striosomes seem to mostly keep track of what the actual outcomes are,” Bloem says. “The decision whether to do an action or not, which essentially requires integrating multiple outcomes, probably happens somewhere downstream in the brain.”

Making judgments

The findings could be relevant not only to mice learning a task, but also to many decisions that people have to make every day as they weigh the risks and benefits of each choice. Eating a big bowl of ice cream after dinner leads to immediate gratification, but it might contribute to weight gain or poor health. Deciding to have carrots instead will make you feel healthier, but you’ll miss out on the enjoyment of the sweet treat.

“From a value perspective, these can be considered equally good,” Bloem says. “What we find is that the striatum also knows why these are good, and it knows what are the benefits and the cost of each. In a way, the activity there reflects much more about the potential outcome than just how likely you are to choose it.”

This type of complex decision-making is often impaired in people with a variety of neuropsychiatric disorders, including anxiety, depression, schizophrenia, obsessive-compulsive disorder, and posttraumatic stress disorder. Drug abuse can also lead to impaired judgment and impulsivity.

“You can imagine that if things are set up this way, it wouldn’t be all that difficult to get mixed up about what is good and what is bad, because there are some neurons that fire when an outcome is good and they also fire when the outcome is bad,” Graybiel says. “Our ability to make our movements or our thoughts in what we call a normal way depends on those distinctions, and if they get blurred, it’s real trouble.”

The new findings suggest that behavioral therapy targeting the stage at which information about potential outcomes is encoded in the brain may help people who suffer from those disorders, the researchers say.

The research was funded by the National Institutes of Health/National Institute of Mental Health, the Saks Kavanaugh Foundation, the William N. and Bernice E. Bumpus Foundation, the Simons Foundation, the Nancy Lurie Marks Family Foundation, the National Eye Institute, the National Institute of Neurological Disease and Stroke, the National Science Foundation, the Simons Foundation Autism Research Initiative, and JSPS KAKENHI.

As with most everything in the world, football looked very different in 2020. As the Covid-19 pandemic unfolded, many National Football League (NFL) games were played in empty stadiums, while other stadiums opened to fans at significantly reduced capacity, with strict safety protocols in place.

At the time it was unclear what impact such large sporting events would have on Covid-19 case counts, particularly at a time when vaccination against the virus was not widely available.

Now, MIT engineers have taken a look back at the NFL’s 2020 regular season and found that for this specific period during the pandemic, opening stadiums to fans while requiring face coverings, social distancing, and other measures had no impact on the number of Covid-19 infections in those stadiums’ local counties.

As they write in a new paper appearing this week in the Proceedings of the National Academy of Sciences, “the benefits of providing a tightly controlled outdoor spectating environment — including masking and distancing requirements — counterbalanced the risks associated with opening.”

The study concentrates on the NFL’s 2020 regular season (September 2020 to early January 2021), at a time when earlier strains of the virus dominated, before the rise of more transmissible Delta and Omicron variants. Nevertheless, the results may inform decisions on whether and how to hold large outdoor gatherings in the face of future public health crises.

“These results show that the measures adopted by the NFL were effective in safely opening stadiums,” says study author Anette “Peko” Hosoi, the Neil and Jane Pappalardo Professor of Mechanical Engineering at MIT. “If case counts start to rise again, we know what to do: mask people, put them outside, and distance them from each other.”

The study’s co-authors are members of MIT’s Institue for Data, Systems, and Society (IDSS), and include Bernardo García Bulle, Dennis Shen, and Devavrat Shah, the Andrew and Erna Viterbi Professor in the Department of Electrical Engineering and Computer Science (EECS).

Preseason patterns

Last year a group led by the University of Southern Mississippi compared Covid-19 case counts in the counties of NFL stadiums that allowed fans in, versus those that did not. Their analysis showed that stadiums that opened to large numbers of fans led to “tangible increases” in the local county’s number of Covid-19 cases.

But there are a number of factors in addition to a stadium’s opening that can affect case counts, including local policies, mandates, and attitudes. As the MIT team writes, “it is not at all obvious that one can attribute the differences in case spikes to the stadiums given the enormous number of confounding factors.”

To truly isolate the effects of a stadium’s opening, one could imagine tracking Covid cases in a county with an open stadium through the 2020 season, then turning back the clock, closing the stadium, then tracking that same county’s Covid cases through the same season, all things being equal.

“That’s the perfect experiment, with the exception that you would need a time machine,” Hosoi says.

As it turns out, the next best thing is synthetic control — a statistical method that is used to determine the effect of an “intervention” (such as the opening of a stadium) compared with the exact same scenario without that intervention.

In synthetic control, researchers use a weighted combination of groups to construct a “synthetic” version of an actual  scenario. In this case, the actual scenario is a county such as Dallas that hosts an open stadium. A synthetic version would be a county that looks similar to Dallas, only without a stadium. In the context of this study, a county that “looks” like Dallas has a similar preseason pattern of Covid-19 cases.

To construct a synthetic Dallas, the researchers looked for surrounding counties without stadiums, that had similar Covid-19 trajectories leading up to the 2020 football season. They combined these counties in a way that best fit Dallas’ actual case trajectory. They then used data from the combined counties to calculate the number of Covid cases for this synthetic Dallas through the season, and compared these counts to the real Dallas.

The team carried out this analysis for every “stadium county.” They determined a county to be a stadium county if more than 10 percent of a stadium’s fans came from that county, which the researchers estimated based on attendance data provided by the NFL.

“Go outside”

Of the stadiums included in the study, 13 were closed through the regular season, while 16 opened with reduced capacity and multiple pandemic requirements in place, such as required masking, distanced seating, mobile ticketing, and enhanced cleaning protocols.

The researchers found the trajectory of infections in all stadium counties mirrored that of synthetic counties, showing that the number of infections would have been the same if the stadiums had remained closed. In other words, they found no evidence that NFL stadium openings led to any increase in local Covid case counts.

To check that their method wasn’t missing any case spikes, they tested it on a known superspreader: the Sturgis Motorcycle Rally, which was held in August of 2020. The analysis successfully picked up an increase in cases in Meade, the host county, compared to a synthetic counterpart, in the two weeks following the rally.

Surprisingly, the researchers found that several stadium counties’ case counts dipped slightly compared to their synthetic counterparts. In these counties — including Hamilton, Ohio, home of the Cincinnati Bengals — it appeared that opening the stadium to fans was tied to a dip in Covid-19 infections. Hosoi has a guess as to why:

“These are football communities with dedicated fans. Rather than stay home alone, those fans may have gone to a sports bar or hosted indoor football gatherings if the stadium had not opened,” Hosoi proposes. “Opening the stadium under those circumstances would have been beneficial to the community because it makes people go outside.”

The team’s analysis also revealed another connection: Counties with similar Covid trajectories also shared similar politics. To illustrate this point, the team mapped the county-wide temporal trajectories of Covid case counts in Ohio in 2020 and found them to be a strong predictor of the state’s 2020 electoral map.

“That is not a coincidence,” Hosoi notes. “It tells us that local political leanings determined the temporal trajectory of the pandemic.”

The team plans to apply their analysis to see how other factors may have influenced the pandemic.

“Covid is a different beast [today],” she says. “Omicron is more transmissive, and more of the population is vaccinated. It’s possible we’d find something different if we ran this analysis on the upcoming season, and I think we probably should try.”

Having trouble hearing? Just turn up your shirt. That’s the idea behind a new “acoustic fabric” developed by engineers at MIT and collaborators at Rhode Island School of Design.

The team has designed a fabric that works like a microphone, converting sound first into mechanical vibrations, then into electrical signals, similarly to how our ears hear.

All fabrics vibrate in response to audible sounds, though these vibrations are on the scale of nanometers — far too small to ordinarily be sensed. To capture these imperceptible signals, the researchers created a flexible fiber that, when woven into a fabric, bends with the fabric like seaweed on the ocean’s surface.

The fiber is designed from a “piezoelectric” material that produces an electrical signal when bent or mechanically deformed, providing a means for the fabric to convert sound vibrations into electrical signals.

The fabric can capture sounds ranging in decibel from a quiet library to heavy road traffic, and determine the precise direction of sudden sounds like handclaps. When woven into a shirt’s lining, the fabric can detect a wearer’s subtle heartbeat features. The fibers can also be made to generate sound, such as a recording of spoken words, that another fabric can detect.   

A study detailing the team’s design appears today in Nature. Lead author Wei Yan, who helped develop the fiber as an MIT postdoc, sees many uses for fabrics that hear.

“Wearing an acoustic garment, you might talk through it to answer phone calls and communicate with others,” says Yan, who is now an assistant professor at the Nanyang Technological University in Singapore. “In addition, this fabric can imperceptibly interface with the human skin, enabling wearers to monitor their heart and respiratory condition in a comfortable, continuous, real-time, and long-term manner.”

Yan’s co-authors include Grace Noel, Gabriel Loke, Tural Khudiyev, Juliette Marion, Juliana Cherston, Atharva Sahasrabudhe, Joao Wilbert, Irmandy Wicaksono, and professors John Joannopoulos and Yoel Fink at MIT, along with Anais Missakian and Elizabeth Meiklejohn at Rhode Island School of Design (RISD), Lei Zhu from Case Western Reserve University, Chu Ma from the University of Wisconsin at Madison, and Reed Hoyt of the U.S. Army Research Institute of Environmental Medicine.

Sound layering

Fabrics are traditionally used to dampen or reduce sound; examples include soundproofing in concert halls and carpeting in our living spaces. But Fink and his team have worked for years to refashion fabric’s conventional roles. They focus on extending properties in materials to make fabrics more functional. In looking for ways to make sound-sensing fabrics, the team took inspiration from the human ear.

Audible sound travels through air as slight pressure waves. When these waves reach our ear, an exquisitely sensitive and complex three-dimensional organ, the tympanic membrane, or eardrum, uses a circular layer of fibers to translate the pressure waves into mechanical vibrations. These vibrations travel through small bones into the inner ear, where the cochlea converts the waves into electrical signals that are sensed and processed by the brain.

Inspired by the human auditory system, the team sought to create a fabric “ear” that would be soft, durable, comfortable, and able to detect sound. Their research led to two important discoveries: Such a fabric would have to incorporate stiff, or “high-modulus,” fibers to effectively convert sound waves into vibrations. And, the team would have to design a fiber that could bend with the fabric and produce an electrical output in the process.

With these guidelines in mind, the team developed a layered block of materials called a preform, made from a piezoelectric layer as well as ingredients to enhance the material’s vibrations in response to sound waves. The resulting preform, about the size of a thick marker, was then heated and pulled like taffy into thin, 40-meter-long fibers.

Lightweight listening

The researchers tested the fiber’s sensitivity to sound by attaching it to a suspended sheet of mylar. They used a laser to measure the vibration of the sheet — and by extension, the fiber — in response to sound played through a nearby speaker. The sound varied in decibel between a quiet library and heavy road traffic. In response, the fiber vibrated and generated an electric current proportional to the sound played.

“This shows that the performance of the fiber on the membrane is comparable to a handheld microphone,” Noel says.

Next, the team wove the fiber with conventional yarns to produce panels of drapable, machine-washable fabric.

“It feels almost like a lightweight jacket — lighter than denim, but heavier than a dress shirt,” says Meiklejohn, who wove the fabric using a standard loom.

She sewed one panel to the back of a shirt, and the team tested the fabric’s sensitivity to directional sound by clapping their hands while standing at various angles to the shirt.

“The fabric was able to detect the angle of the sound to within 1 degree at a distance of 3 meters away,” Noel notes.

The researchers envision that a directional sound-sensing fabric could help those with hearing loss to tune in to a speaker amid noisy surroundings.

The team also stitched a single fiber to a shirt’s inner lining, just over the chest region, and found it accurately detected the heartbeat of a healthy volunteer, along with subtle variations in the heart’s S1 and S2, or “lub-dub” features. In addition to monitoring one’s own heartbeat, Fink sees possibilities for incorporating the acoustic fabric into maternity wear to help monitor a baby’s fetal heartbeat.

Finally, the researchers reversed the fiber’s function to serve not as a sound-detector but as a speaker. They recorded a string of spoken words and fed the recording to the fiber in the form of an applied voltage. The fiber converted the electrical signals to audible vibrations, which a second fiber was able to detect. 

In addition to wearable hearing aids, clothes that communicate, and garments that track vital signs, the team sees applications beyond clothing.

“It can be integrated with spacecraft skin to listen to (accumulating) space dust, or embedded into buildings to detect cracks or strains,” Yan proposes. “It can even be woven into a smart net to monitor fish in the ocean. The fiber is opening widespread opportunities.”

“The learnings of this research offers quite literally a new way for fabrics to listen to our body and to the surrounding environment,” Fink says. “The dedication of our students, postdocs and staff to advancing research which has always marveled me is especially relevant to this work, which was carried out during the pandemic.”

This research was supported in part by the US Army Research Office through the Institute for Soldier Nanotechnologies, National Science Foundation, Sea Grant NOAA.