Transistors, the building blocks of modern electronics, are typically made of silicon. Because it’s a semiconductor, this material can control the flow of electricity in a circuit. But silicon has fundamental physical limits that restrict how compact and energy-efficient a transistor can be.

MIT researchers have now replaced silicon with a magnetic semiconductor, creating a magnetic transistor that could enable smaller, faster, and more energy-efficient circuits. The material’s magnetism strongly influences its electronic behavior, leading to more efficient control of the flow of electricity. 

The team used a novel magnetic material and an optimization process that reduces the material’s defects, which boosts the transistor’s performance.

The material’s unique magnetic properties also allow for transistors with built-in memory, which would simplify circuit design and unlock new applications for high-performance electronics.

“People have known about magnets for thousands of years, but there are very limited ways to incorporate magnetism into electronics. We have shown a new way to efficiently utilize magnetism that opens up a lot of possibilities for future applications and research,” says Chung-Tao Chou, an MIT graduate student in the departments of Electrical Engineering and Computer Science (EECS) and Physics, and co-lead author of a paper on this advance.

Chou is joined on the paper by co-lead author Eugene Park, a graduate student in the Department of Materials Science and Engineering (DMSE); Julian Klein, a DMSE research scientist; Josep Ingla-Aynes, a postdoc in the MIT Plasma Science and Fusion Center; Jagadeesh S. Moodera, a senior research scientist in the Department of Physics; and senior authors Frances Ross, TDK Professor in DMSE; and Luqiao Liu, an associate professor in EECS, and a member of the Research Laboratory of Electronics; as well as others at the University of Chemistry and Technology in Prague. The paper appears today in Physical Review Letters.

Overcoming the limits

In an electronic device, silicon semiconductor transistors act like tiny light switches that turn a circuit on and off, or amplify weak signals in a communication system. They do this using a small input voltage.

But a fundamental physical limit of silicon semiconductors prevents a transistor from operating below a certain voltage, which hinders its energy efficiency.

To make more efficient electronics, researchers have spent decades working toward magnetic transistors that utilize electron spin to control the flow of electricity. Electron spin is a fundamental property that enables electrons to behave like tiny magnets.

So far, scientists have mostly been limited to using certain magnetic materials. These lack the favorable electronic properties of semiconductors, constraining device performance.

“In this work, we combine magnetism and semiconductor physics to realize useful spintronic devices,” Liu says.

The researchers replace the silicon in the surface layer of a transistor with chromium sulfur bromide, a two-dimensional material that acts as a magnetic semiconductor.

Due to the material’s structure, researchers can switch between two magnetic states very cleanly. This makes it ideal for use in a transistor that smoothly switches between “on” and “off.”

“One of the biggest challenges we faced was finding the right material. We tried many other materials that didn’t work,” Chou says.

They discovered that changing these magnetic states modifies the material’s electronic properties, enabling low-energy operation. And unlike many other 2D materials, chromium sulfur bromide remains stable in air.

To make a transistor, the researchers pattern electrodes onto a silicon substrate, then carefully align and transfer the 2D material on top. They use tape to pick up a tiny piece of material, only a few tens of nanometers thick, and place it onto the substrate.

“A lot of researchers will use solvents or glue to do the transfer, but transistors require a very clean surface. We eliminate all those risks by simplifying this step,” Chou says.

Leveraging magnetism

This lack of contamination enables their device to outperform existing magnetic transistors. Most others can only create a weak magnetic effect, changing the flow of current by a few percent or less. Their new transistor can switch or amplify the electric current by a factor of 10.

They use an external magnetic field to change the magnetic state of the material, switching the transistor using significantly less energy than would usually be required.

The material also allows them to control the magnetic states with electric current. This is important because engineers cannot apply magnetic fields to individual transistors in an electronic device. They need to control each one electrically.

The material’s magnetic properties could also enable transistors with built-in memory, simplifying the design of logic or memory circuits.

A typical memory device has a magnetic cell to store information and a transistor to read it out. Their method can combine both into one magnetic transistor.

“Now, not only are transistors turning on and off, they are also remembering information. And because we can switch the transistor with greater magnitude, the signal is much stronger so we can read out the information faster, and in a much more reliable way,” Liu says.

Building on this demonstration, the researchers plan to further study the use of electrical current to control the device. They are also working to make their method scalable so they can fabricate arrays of transistors.

This research was supported, in part, by the Semiconductor Research Corporation, the U.S. Defense Advanced Research Projects Agency (DARPA), the U.S. National Science Foundation (NSF), the U.S. Department of Energy, the U.S. Army Research Office, and the Czech Ministry of Education, Youth, and Sports. The work was partially carried out at the MIT.nano facilities.

This is a current list of where and when I am scheduled to speak:

• I’m giving the Ross Anderson Lecture at the University of Cambridge’s Churchill College at 5:30 PM GMT on Thursday, March 19, 2026.
• I’m speaking at RSAC 2026 in San Francisco, California, USA, on Wednesday, March 25, 2026.
• I’m part of an event on “Canada and AI Sovereignty,” hosted by the University of Toronto’s Munk School of Global Affairs & Public Policy, which will be held online via Zoom at 4:00 PM ET on Monday, March 30, 2026.
• I’m speaking at DemocracyXChange 2026...

Vineyard Wind and Revolution Wind, the nation's largest wind projects, are generating power off the New England coast.

Some good news: squid stocks seem to be recovering in the waters off the Falkland Islands.

As usual, you can also use this squid post to talk about the security stories in the news that I haven’t covered.

Blog moderation policy.

The Financial Times has placed MIT Sloan School of Management at the top of its recently released 2026 Global MBA Ranking. It is the school’s first time gaining the No. 1 spot in the list.

In its announcement of the rankings, the publication noted MIT’s school of management tops the list “at a time of sharpening focus from students on the importance of technology, including artificial intelligence, as they prepare for disruptions in the workplace.”

Global education editor Andrew Jack said in the Financial Times News Briefing podcast that MIT is “very much at the center of the tech revolution that we are seeing.” He added, “there’s no question that we’re talking more and more about artificial intelligence and expertise around some of the technical skills related and notably how you might apply AI in the workplace. That certainly reflects both its technical and engineering computer science skills historically. And [MIT Sloan] is doing a lot with those other departments in the university. So I think that says something very much about how the wider job market and the aspirations of students are evolving.”

“MIT Sloan operates at the intersection of management and technology,” says Richard Locke, the John C Head III Dean of the MIT Sloan School of Management. “Our students and alumni are employing artificial intelligence to solve complex problems in the world and across industries. At MIT Sloan, we focus on doing that work in a way that centers human capabilities, ensuring artificial intelligence extends what humans can do to improve organizations and the world.”

To determine its rankings, the Financial Times considers 21 criteria. Eight of those — accounting for 56 percent of the ranking’s weight — are determined by surveying alumni three years after they have completed their MBA program. School data are used for 34 percent percent of the rank. The remaining 10 percent measures how often full-time faculty publish in top journals.

MIT Sloan ranked fourth for its alumni network, which measures how effectively alumni support one another through career advice, internships, job opportunities, and recruiting efforts. 

“This ranking underscores the strength of our global alumni community,” says Kathy Hawkes, senior associate dean of external engagement. “'Sloanies Helping Sloanies' isn’t just a phrase — it’s a lived experience. Our 31,000 alumni actively open doors, share expertise, and invest in each other’s success.”

MIT researchers have discovered that two common genetic mutations that cause Rett syndrome each set off a molecular chain of events that compromises the structural integrity of developing brain blood vessels, making them leaky. The study traces the problem to overexpression of a particular microRNA (miRNA-126-3p), and shows that tamping down the miRNA’s levels helps to rescue the vascular defect.

Rett syndrome is a severe developmental disorder affecting both the brain and body. It is caused by various mutations in the widely expressed MECP2 gene, but the first symptoms don’t become apparent until affected children (mostly girls) reach 2-3 years of age. Because that’s a critical time in development for the brain’s blood vessels, neuroscientists in The Picower Institute for Learning and Memory at MIT embarked on a study to model how two common but distinct MeCP2 mutations may affect vascular development and contribute to the disease’s profound neurological pathology.

To conduct the research published recently in Molecular Psychiatry, lead author Tatsuya Osaki and senior author Mriganka Sur developed advanced human tissue cultures to model vessel development, with and without the MeCP2 mutations. The cultures not only enabled them to model and closely observe how the mutations affected the vessels, but also allowed them to molecularly dissect the problems they observed and then to test an intervention that helped.

“A role for microRNAs in Rett syndrome has been shown, but now demonstrating that miRNA-126-3p is actually downstream of MeCP2 and directly implicated in the endothelial cell dysfunction is an important piece of the Rett syndrome puzzle,” says Sur, the Newton Professor of Neuroscience in the Picower Institute and MIT’s Department of Brain and Cognitive Sciences.

Building vessels and spotting leaks

Building on years of tissue engineering experience, including time as a postdoc in the lab of co-author and MIT mechanical engineering and biological engineering Professor Roger D. Kamm, Osaki built “3-dimensional microvascular networks” using human induced pluripotent stem cells (iPS cells) donated by patients with Rett syndrome. The donated cells were induced to become stem cells, and then endothelial cells (the backbone of blood vessels). Embedded in a gel and mixed with fibroblast cells, the endothelial cells self-assembled into networks of tubes, which Osaki then hooked up to microfluidics to provide circulation.

One set of the cultures harbored the mutation R306C. Osaki created a control microvasculature that was genetically identical except that it did not have the mutation. Another set of the cultures had the R168X mutation. And again, Osaki paired that with control culture that was identical except for the mutation using CRISPR.

The research team chose these two mutations because they are each relatively common but affect the MeCP2 gene differently, Sur says. The finding that each of these distinct Rett-causing mutations ultimately led to upregulating miRNA-126-3p and undermining blood vessel integrity suggests that vascular problems are indeed a central feature of the disease.

“There is something common across these mutations,” Sur says.

In particular, lab tests showed that the vessels harboring either mutation showed reduced expression of a protein called ZO-1, which is critical for ensuring that the junctions among endothelial cells in blood vessels form a tight seal (like the grout in a tile floor). ZO-1 also didn’t localize to those junctions as well. Sure enough, further tests showed that the Rett-mutation vessel cultures were relatively leaky compared to the controls.

Similar deficiencies were evident in another cell culture the team created, in which they added astrocyte cells to even more closely simulate the blood-brain-barrier (BBB), which tightly regulates what can go in or out of blood vessels and into the brain. BBB problems are widely suspected of contributing to neurodegenerative diseases such as Alzheimer’s, Huntington’s, and ALS and frontotemporal dementia.

To gain some insight into how the vascular problems might undermine neural function in Rett syndrome, the researchers exposed neurons to medium from their Rett vasculature cultures. Those nerve cells showed reduced electrical activity, a possible sign that secretions from the Rett endothelial cells disrupted the neurons.

Catching a culprit

Generally speaking, the role of MeCP2 is to repress the expression of other genes. The scientists’ expectation, therefore, was that when MeCP2 is compromised by mutations the result would be overexpression of many genes. Yet ZO-1 was downregulated. Something had to account for that and miRNAs were a suspect, Osaki says, because they function as regulators of gene expression.

“That’s why we hypothesized that we should have some mediator between the MeCP2 mutation and ZO-1 downregulation and the BBB permeability increase,” Osaki says. “We focused on the microRNAs.”

Indeed, by profiling miRNAs in the Rett cultures and the controls, the scientists found that miRNA-126-3p was overexpressed. And by sequencing RNA, the team identified more molecular pathways needed to support vascular integrity that were dysregulated in the Rett cultures.

While the sequencing and profile associated miRNA-126-3p upregulation with the altered molecular chain of events, Osaki and Sur sought more definitive proof. To obtain it, they treated the Rett-mutation cultures with an “antisense” — a molecule that reduces miRNA-126-3p levels. Doing that resulted in an increase in ZO-1 expression and a partial restoration of endothelial cell barrier function — meaning less leakiness — in the vessel cultures. Knocking down the miRNA’s expression also restored the molecular pathways the scientists were tracking to more healthy states.

It turns out that there is a drug that inhibits miR-126 called miRisten that is undergoing clinical testing for leukemia. Osaki and Sur say they are planning on administering it to mice modeling Rett syndrome to see if it helps them.

In addition to Osaki, Sur, and Kamm, the paper’s co-authors are Zhengpeng Wan, Koji Haratani, Ylliah Jin, Marco Campisi, and David Barbie.

Funding for the study came from sources including the National Institutes of Health, a MURI grant, The Freedom Together Foundation, and the Simons Center for the Social Brain.

EFF is filing against the Consumer Product Safety Council (CPSC) to ensure that the public has full access to the laws that govern us.

Our client Public.Resource.Org (Public Resource), a tiny non-profit founded by open records advocate Carl Malamud, has a mission that’s both simple and powerful: to make government information more accessible. Public Resource acquires and makes available online a wide variety of public documents such as tax filings, government-produced videos, and federal rules about safety and product designs. Those rules are initially created through private standards organizations and later incorporated into federal law. Such documents are often difficult to access otherwise, meaning the public cannot read, share, or comment on them. 

Working with Harvard Law School’s Cyberlaw Clinic, Public Resource has been submitting Freedom of Information Act requests to the CPSC requesting copies of the legally binding safety codes for children’s products—an area of law of intense interest to child safety advocates and consumer advocates, not to mention the families who use those products. But CPSC says it can’t release the codes, because the private association that coordinated their initial development insists that it retains copyright in them even after they have been adopted into law. That’s like saying a lobbyist who drafted a new tax law gets to control who reads it or shares it, even after it becomes a legal mandate.

Faced with similar claims, some courts, including the Court of Appeals for the Fifth Circuit, have held that the safety codes lose copyright protection when they are incorporated into law. Others, like the D.C. Circuit (in a case EFF defended on Public Resource’s behalf), have held that even if the standards lose copyright once they are incorporated into law, making them fully accessible and usable online is a lawful fair use. 

Now EFF has teamed up with the Cyberlaw Clinic to continue the fight. We’re asking a court to rule that copyright is no barrier to accessing and sharing the rules that are supposed to ensure the safety of our built environment and the products we use every day. With the rule of law under assault around the nation, it is more important than ever to defend our ability to read and speak the law, without restrictions.

Geothermal energy, a clean, continuous energy source accessible in many locations, has been slow to catch on. Nearly 2,000 years ago, the Romans made extensive use of geothermal energy — heat from the Earth — including at the spa complex at present-day Bath, England. Electricity was first produced from geothermal sources in the early 1900s in Italy. In the United States, the Geysers geothermal field in California began generating electricity at scale in 1960, and routinely produces more than 725 megawatts of baseload power today. 

According to the International Energy Agency (IEA), geothermal energy still supplies less than 1 percent of global electricity demand, although countries like Kenya (more than 40 percent of electricity generation) and Iceland (nearly 30 percent of electricity and 90 percent of the heating) have seen widespread adoption.

In recent years, technological advances, an influx of private capital, and shifting energy and environmental policies have driven renewed interest in expanding development of geothermal energy. If project costs continue to decline, the IEA predicts that geothermal energy could meet 15 percent of the growth in global electricity demand between 2024 and 2050. Many countries, including the United States, Indonesia, New Zealand, and Turkey, are prioritizing an expansion of geothermal energy as part of their broader energy strategies.

Achieving large-scale electricity generation from geothermal sources will depend on a significant expansion of so-called next-generation geothermal. This refers to tapping heat from source rocks at temperatures of 100 degrees Celsius to more than 400 C, often at depths of several kilometers below the surface. Last month, U.S. Congressional Rep. Jake Auchincloss (D-MA) and Rep. Mark Amodei (R-NV) introduced bipartisan legislation to promote research, testing, and development of one type of next-generation geothermal energy known as superhot rock.

Geothermal energy at MIT

Through its leadership in producing the influential 2006 “The Future of Geothermal Energy” report led by former MIT professor Jeff Tester, MIT and the predecessor of the MIT Energy Initiative (MITEI) played an important role in national geothermal strategy two decades ago. In 2008, researchers at the Plasma Science and Fusion Center (PSFC) invented millimeter-wave drilling with support from one of the first MITEI seed innovation grants. The technology, which could be particularly useful for geothermal installations in superhot and deep rock, is being commercialized by MIT spinout Quaise Energy.

MITEI is sponsoring next-generation geothermal projects through its Future Energy Systems Center. A project led by MITEI Research Scientist Pablo Duenas-Martinez focuses on the techno-economics of electricity generation from a geothermal plant co-located with a data center, a timely topic given the proliferation of data center power purchase agreements for electricity generated by geothermal energy. MITEI’s March 4 Spring Symposium focused on next-geothermal energy for the generation of firm power, and many of the leading exploration, drilling, reservoir development, and advanced technology companies working in this area sent panelists and speakers. On March 5, MITEI collaborated with the Clean Air Task Force (CATF) to co-host the GeoTech Summit, which explored accelerating technology development for and investment in next-generation geothermal.

To prepare for the recent symposium, MITEI organized a geothermal bootcamp during MIT’s Independent Activities Period (IAP) that introduced more than 40 members of the MIT community to geothermal basics, key technologies, and related MIT research. Carolyn Ruppel, MITEI’s deputy director of science and technology and the organizer of the IAP bootcamp and Spring Symposium, says, “MITEI’s member companies, which represent leading voices on energy, power generation, infrastructure, heavy industry, and digital technology, are increasingly approaching us about their interest in next-generation geothermal. There is also good momentum building across MIT, ranging from projects at the Earth Resources Laboratory to the millimeter-wave testbed being developed by PSFC and its MIT collaborators, individual projects in academic departments, and of course the work MITEI has been funding.”

Geothermal basics

Temperatures a few tens of meters below the ground are typically stable year-round. In some locations, these temperatures are warmer than the surface in winter and cooler in summer, making it possible to use geothermal heat pumps to moderate temperatures in buildings throughout the year. Overlooking the Charles River, Boston University’s 19-story Center for Computing and Data Science meets an estimated 90 percent of its heating and cooling needs using this kind of geothermal system. At the scale of large institutions or whole towns, thermal networks, district heating, and other approaches can efficiently supply heat from shallow geothermal sources without producing greenhouse gas emissions.

Tapping hotter and usually deeper geothermal sources could generate large amounts of electricity for decades at a single site. Next-generation geothermal is the term applied to these higher-temperature systems developed using enhanced, advanced, and superhot technologies. Enhanced geothermal refers to circulating fluids through engineered fracture systems in deep, dry rock with relatively low native permeability. Advanced geothermal adopts a closed loop approach, in which a working fluid is heated by circulating it through pipes embedded in the subsurface. Superhot geothermal, which is in its infancy, will likely use enhanced geothermal technology to circulate supercritical water through rock at almost 400 C.   

Next-generation geothermal

Drill deep enough and higher-temperature resources are nearly ubiquitous beneath the continents, but early-stage development must focus on the most promising sites, where the methods and technologies to routinely reach these hotter rocks can be tested and refined. Locations like Iceland and the southwestern U.S. state of Nevada, where tectonic plates are separating or the Earth’s outer layer is thinning, have hotter temperatures closer to the surface than areas like the northeastern United States, where the Earth’s crust is old, thick, and cooler. Even in the southwestern United States, though, reaching the high temperatures required for generating electricity via geothermal systems will require routinely drilling to depths of greater than 4 kilometers in crystalline rock. This is significantly more challenging than drilling in the sedimentary basins that host most of the world’s oil and gas reserves. 

For a location to be suitable for a next-generation geothermal installation requires not only heat, but also a fluid (usually water) to carry the heat. Water circulated through the rock formation to extract heat can be present naturally or brought from elsewhere and injected into the reservoir. This type of system also requires connected permeability such as an engineered fracture network oriented to prevent significant fluid losses and to channel fluid toward the extraction well. Closed-loop (advanced) systems replace the freely circulating water with a working fluid that has favorable thermal characteristics and that is confined in piping.

Various geophysical methods are used to find sites with sufficient heat within a few kilometers of the surface, a prerequisite for their development as next-generation geothermal installations. Apart from direct measurements of temperatures in test boreholes, electrical resistivity and magnetotelluric surveys are among the most useful for inferring subsurface temperature regimes. Both techniques infer the electrical conductivity structure beneath the ground, permitting the identification of relatively warmer and more permeable rocks.

Drilling is often the most time-consuming and expensive part of preparing a site for a geothermal plant. This is particularly true for next-generation geothermal, where the targets can be deep, or the system design may require large-scale horizontal drilling. Over the past few years, numerous innovations have increased drilling rates and attainable depths and temperatures and also lowered costs. Nonetheless, even with high-quality geophysical surveys, “you may spend $10 million on an exploratory well and find no heat,” says Andrew Inglis, the geothermal channel venture builder at MIT Proto Ventures. 

Superhot geothermal, a next-generation geothermal approach that is advancing rapidly, presents special challenges. The metal drilling tools, the rocks in the formation, and circulating fluids all behave differently at temperatures of several hundred degrees, and standard practices, materials, and sensors must be significantly modified to tolerate the tough conditions. Once temperatures exceed 374 C in a borehole even ~1 km deep, water reaches a supercritical state. This presents substantial advantages for extracting heat from the formation, but introduces the specter of rapid metal corrosion and precipitation of salts and silica that can quickly foul a borehole. Researchers are investigating substitution of supercritical carbon dioxide for water as a working fluid for superhot geothermal.

MIT innovations advancing next-generation geothermal

The millimeter-wave drilling technology invented at PSFC and being commercialized by Quaise Energy is the highest-profile next-generation geothermal innovation to emerge from MIT so far. Millimeter-wave technology uses microwave energy to vaporize rock and could prove to be several times faster than conventional drilling. PSFC and a multidisciplinary MIT team are devising a dedicated laboratory to study how millimeter-wave drilling interacts with crystalline rock at realistic pressure and temperature conditions, and to test improvements to the existing technology. Steve Wukitch, interim director and principal research scientist at PSFC, notes that “the facility we are building at MIT will allow us to test samples 500 times larger than is currently possible. This is an important step for investigating technologies that could unlock superhot geothermal energy."

MIT Proto Ventures, which focuses on creating startups based on technology invented at MIT, currently hosts a dedicated geothermal energy channel led by Inglis. Since arriving at MIT in late 2024, Inglis has identified inventions and research that could advance next-generation geothermal from disciplines as disparate as mechanical and materials engineering, earth sciences, and chemistry. Examples of technologies originating with MIT researchers include sensors that measure micro-cracking in high-temperature rock, advanced metal alloys that could handle superhot fluids at a fraction of the cost of titanium, and anti-fouling coatings to protect pipes from the caustic geofluids common in hot, deep systems.

MITEI Spring Symposium

At the recent MITEI Spring Symposium, these MIT innovators introduced their technology to MITEI member companies in a session led by Inglis. Wukitch, who moderated a panel on advanced drilling, described the planned millimeter-wave testbed, and Duenas-Martinez led a panel on power generation and storage. Terra Rogers, director for superhot rock geothermal energy at the CATF and the organizer of the joint CATF-MITEI GeoTech Summit on March 5, led a discussion of international and U.S. policies and the regulatory environment for expansion of next-generation geothermal. 

Poster presenters included MIT graduate students and researchers, MIT’s D-Lab, and the Geo@MIT geothermal-focused MIT student group, which was recognized with a 2024 bonus award by the U.S. Department of Energy’s Geothermal Technologies Office in the nationwide EnergyTech University Prize competition.  

In 2025, Google, Amazon, Microsoft and Meta collectively spent US$380 billion on building artificial-intelligence tools. That number is expected to surge still higher this year, to $650 billion, to fund the building of physical infrastructure, such as data centers (see go.nature.com/3lzf79q). Moreover, these firms are spending lavishly on one particular segment: top technical talent.

Meta reportedly offered a single AI researcher, who had cofounded a start-up firm focused on training AI agents to use computers, a compensation package of $250 million over four years (see ...

The conflict threatens to deflate global confidence in natural gas as President Donald Trump hopes to expand U.S. exports.

A former Trump energy adviser is urging the administration to study and regulate solar geoengineering before an adversary weaponizes it.

Republican state attorneys general say two of the nation’s leading scientific bodies helped develop educational materials that favor climate activists.

Republican lawmakers are rushing to defend an agency that has been under administration scrutiny.

The lawsuit is the Trump administration's latest challenge to state action on climate change.

Environmental and scientific groups can still access the underlying data and haven't shown an injury to sue over, the judge ruled.

The automotive package limits technological neutrality, while the Industrial Accelerator Act will hinder exports, CEO Oliver Zipse argues.

It's unclear if Sublime Systems can fulfill a deal with Microsoft to supply as much as 622,500 metric tons of cement over five to eight years.

The phenomenon is poised to add extra warmth to a planet that’s rapidly heating due to human-caused climate change.

Temperatures in Cape Town climbed to 108 degrees Fahrenheit on Wednesday, the highest since records began 66 years ago.

MIT neuroscientists have figured out how the brain is able to focus on a single voice among a cacophony of many voices, shedding light on a longstanding neuroscientific phenomenon known as the cocktail party problem.

This attentional focus becomes necessary when you’re in any crowded environment, such as a cocktail party, with many conversations going on at once. Somehow, your brain is able to follow the voice of the person you’re talking to, despite all the other voices that you’re hearing in the background.

Using a computational model of the auditory system, the MIT team found that amplifying the activity of the neural processing units that respond to features of a target voice, such as its pitch, allows that voice to be boosted to the forefront of attention.

“That simple motif is enough to cause much of the phenotype of human auditory attention to emerge, and the model ends up reproducing a very wide range of human attentional behaviors for sound,” says Josh McDermott, a professor of brain and cognitive sciences at MIT, a member of MIT’s McGovern Institute for Brain Research and Center for Brains, Minds, and Machines, and the senior author of the study.

The findings are consistent with previous studies showing that when people or animals focus on a specific auditory input, neurons in the auditory cortex that respond to features of the target stimulus amplify their activity. This is the first study to show that extra boost is enough to explain how the brain solves the cocktail party problem.

Ian Griffith, a graduate student in the Harvard Program in Speech and Hearing Biosciences and Technology, who is advised by McDermott, is the lead author of the paper. MIT graduate student R. Preston Hess is also an author of the paper, which appears today in Nature Human Behavior.

Modeling attention

Neuroscientists have been studying the phenomenon of selective attention for decades. Many studies in people and animals have shown that when focusing on a particular stimulus like the sound of someone’s voice, neurons that are tuned to features of that voice — for example, high pitch — amplify their activity.

When this amplification occurs, neurons’ firing rates are scaled upward, as though multiplied by a number greater than one. It has been proposed that these “multiplicative gains” allow the brain to focus its attention on certain stimuli. Neurons that aren’t tuned to the target feature exhibit a corresponding reduction in activity.

“The responses of neurons tuned to features that are in the target of attention get scaled up,” Griffith says. “Those effects have been known for a very long time, but what’s been unclear is whether that effect is sufficient to explain what happens when you’re trying to pay attention to a voice or selectively attend to one object.”

This question has remained unanswered because computational models of perception haven’t been able to perform attentional tasks such as picking one voice out of many. Such models can readily perform auditory tasks when there is an unambiguous target sound to identify, but they haven’t been able to perform those tasks when other stimuli are competing for their attention.

“None of our models has had the ability that humans have, to be cued to a particular object or a particular sound and then to base their response on that object or that sound. That’s been a real limitation,” McDermott says.

In this study, the MIT team wanted to see if they could train models to perform those types of tasks by enabling the model to produce neuronal activity boosts like those seen in the human brain.

To do that, they began with a neural network that they and other researchers have used to model audition, and then modified the model to allow each of its stages to implement multiplicative gains. Under this architecture, the activation of processing units within the model can be boosted up or down depending on the specific features they represent, such as pitch.

To train the model, on each trial the researchers first fed it a “cue”: an audio clip of the voice that they wanted the model to pay attention to. The unit activations produced by the cue then determined the multiplicative gains that were applied when the model heard a subsequent stimulus.

“Imagine the cue is an excerpt of a voice that has a low pitch. Then, the units in the model that represent low pitch would get multiplied by a large gain, whereas the units that represent high pitch would get attenuated,” Griffith says.

Then, the model was given clips featuring a mix of voices, including the target voice, and asked to identify the second word said by the target voice. The model activations to this mixture were multiplied by the gains that resulted from the previous cue stimulus. This was expected to cause the target voice to be “amplified” within the model, but it was not clear whether this effect would be enough to yield human-like attentional behavior.

The researchers found that under a variety of conditions, the model performed very similarly to humans, and it tended to make errors similar to those that humans make. For example, like humans, it sometimes made mistakes when trying to focus on one of two male voices or one of two female voices, which are more likely to have similar pitches.

“We did experiments measuring how well people can select voices across a pretty wide range of conditions, and the model reproduces the pattern of behavior pretty well,” Griffith says.

Effects of location

Previous research has shown that in addition to pitch, spatial location is a key factor that helps people focus on a particular voice or sound. The MIT team found that the model also learned to use spatial location for attentional selection, performing better when the target voice was at a different location from distractor voices.

The researchers then used the model to discover new properties of human spatial attention. Using their computational model, the researchers were able to test all possible combinations of target locations and distractor locations, an undertaking that would be hugely time-consuming with human subjects.

“You can use the model as a way to screen large numbers of conditions to look for interesting patterns, and then once you find something interesting, you can go and do the experiment in humans,” McDermott says.

These experiments revealed that the model was much better at correctly selecting the target voice when the target and distractor were at different locations in the horizontal plane. When the sounds were instead separated in the vertical plane, this task became much more difficult. When the researchers ran a similar experiment with human subjects, they observed the same result.

“That was just one example where we were able to use the model as an engine for discovery, which I think is an exciting application for this kind of model,” McDermott says.

Another application the researchers are pursuing is using this kind of model to simulate listening through a cochlear implant. These studies, they hope, could lead to improvements in cochlear implants that could help people with such implants focus their attention more successfully in noisy environments.

The research was funded by the National Institutes of Health.