“There’s a folk psychology or tacit assumption that what anesthesia does is simply ‘turn off’ the brain,” said Earl Miller, Picower Professor of Neuroscience and co-senior author of the study in eLife. “What we show is that propofol dramatically changes and controls the dynamics of the brain’s rhythms.”

Conscious functions, such as perception and cognition, depend on coordinated brain communication, in particular between the thalamus and the brain’s surface regions, or cortex, in a variety of frequency bands ranging from 4 to 100 Hz. Propofol, the study shows, seems to bring coordination among the thalamus and cortical regions down to frequencies around just 1 Hz.

Miller’s lab, led by postdoc Andre Bastos and former graduate student Jacob Donoghue, collaborated with that of co-senior author Emery N. Brown, who is Edward Hood Taplin Professor of Medical Engineering and Computational Neuroscience and an anesthesiologist at Massachusetts General Hospital. The collaboration therefore powerfully unified the Miller lab’s expertise on how neural rhythms coordinate the cortex to produce conscious brain function with the Brown lab’s expertise in the neuroscience of anesthesia and statistical analysis of neural signals.

Brown said studies that show how anesthetics change brain rhythms can directly improve patient safety because these rhythms are readily visible on the EEG in the operating room. The study’s main finding of a signature of very slow rhythms across the cortex offers a model for directly measuring when subjects have entered unconsciousness after propofol administration, how deeply they are being maintained in that state, and how quickly they may wake up once propofol dosing ends.

“Anesthesiologists can use this as a way to better take care of patients,” Brown said.

Brown has long studied how brain rhythms are affected in humans under general anesthesia by making and analyzing measurements of rhythms using scalp EEG electrodes and to a limited extent, cortical electrodes in epilepsy patients. Because the new study was conducted in animal models of those dynamics, the team was able to implant electrodes that could directly measure the activity or “spiking” of many individual neurons and rhythms in the cortex and thalamus. Brown said the results therefore significantly deepen and extend his findings in people.

For instance, the same neurons that they measured chattering away with spikes of voltage 7-10 times a second during wakefulness routinely fired only once a second or less during propofol-induced unconsciousnesss, a notable slowing called a “down state.” In all, the scientists made detailed simultaneous measurements of rhythms and spikes in five regions: two in the front of the cortex, two toward the back, and the thalamus.

“What’s so compelling is we are getting data down to the level of spikes,” Brown said. “The slow oscillations modulate the spiking activity across large parts of the cortex.”

As much as the study explains how propofol generates unconsciousness, it also helps to explain the unified experience of consciousness, Miller said.

“All the cortex has to be on the same page to produce consciousness,” Miller said. “One theory about how this works is through thalamo-cortical loops that allow the cortex to synchronize. Propofol may be breaking the normal operation of those loops by hyper synchronizing them in prolonged down states. It disrupts the ability of the cortex to communicate.”

For instance, by making measurements in distinct layers of the cortex, the team found that higher frequency “gamma” rhythms, which are normally associated with new sensory information like sights and sounds, were especially reduced in superficial layers. Lower frequency “alpha” and “beta” waves, which Miller has shown tend to regulate the processing of the information carried by gamma rhythms, were especially reduced in deeper layers.

In addition to the prevailing synchrony at very slow frequencies, the team noted other signatures of unconsciousness in the data. As Brown and others have observed in humans before, alpha and beta rhythm power was notably higher in posterior regions of the cortex during wakefulness, but after loss of consciousness power at those rhythms flipped to being much higher in anterior regions.

The team further showed that stimulating the thalamus with a high frequency pulse of current (180Hz) undid propofol’s effects.

“Stimulation produced an awake-like cortical state by increasing spiking rates and decreasing slow-frequency power,” the authors wrote in the study. “In all areas, there was a significant increase in spiking during the stimulation interval compared to pre-stimulation baseline.”

Researchers from the Institute of Neurosciences of the University of Barcelona (UBNeuro) and the Sant Joan de Déu Research Institute (IRSJD) have created a new methodology to try to answer this basic question on human development.

The results, published in the Nature’s open-access journal Scientific Reports, confirm that newborn neural encoding of voice pitch is comparable to the adults’ sabilities after three years of being exposed to language. However, there are differences regarding the perception of spectral and temporal fine structures of sounds, which consists on the ability to distinguish between vocal sounds such as /o/ and /a/. Therefore, according to the authors, neural encoding of this sound aspect, recorded for the first time in this study, is not found mature enough after being born, but it needs a certain exposure to the language as well as stimulation and time to develop.

According to the researchers, knowing the level of development typical in these neural encoding processes from birth will enable them to make an “early detection of language impairments, which would provide an early intervention or stimulus to reduce future negative consequences.”

The study is led by Carles Escera, professor of Cognitive Neuroscience at the Department of Clinical Psychology and Psychobiology of the UB, and has been carried out at the IRSJD, in collaboration with Maria Dolores Gómez Roig, head of the Department of Obstetrics and Gynecology of Hospital Sant Joan de Déu. The study is also signed by the experts Sonia Arenillas Alcón, first author of the article, Jordi Costa Faidella and Teresa Ribas Prats, all members of the Cognitive Neuroscience Research Group (Brainlab) of the UB.

Decoding the spectral and temporal fine structure of sound

In order to distinguish the neural response to speech stimuli in newborns, one of the main challenges was to record, using the baby’s electroencephalogram, a specific brain response: the frequency-following response (FFR). The FFR provides information on the neural encoding of two specific features of sound: fundamental frequency, responsible for the perception of voice pitch (high or low), and the spectral and temporal fine structure. The precise encoding of both features is, according to the study, “fundamental for the proper perception of speech, a requirement in future language acquisition.”

To date, the available tools to study this neural encoding enabled researchers to determine whether the newborn’s baby was able to encode inflections in the voice pitch, but it did not when it came to the spectral and temporal fine structure. “Inflections in voice pitch contour are very important, especially in tonal variations like in Mandarin, as well as to perceive the prosody from speech that transmits emotional content of what is said. However, the spectral and temporal fine structure of sound is the most relevant aspect in language acquisition regarding non-tonal languages like ours, and the few existing studies on the issue do not inform about the precision with which a newborn’s brain encodes it,” note the authors.

The main cause of this lack of studies is the technical limitation caused by the type of sounds used to conduct these tests. Therefore, authors have developed a new stimulus (/oa/) whose internal structure (increasing change in voice pitch, two different vocals) allows them to evaluate the precision of the neural encoding of both features of the sound simultaneously using the FFR analysis.

An adapted test to the limitations of the hospital environment

One of the most highlighted aspects of the study is that the stimulus and the methodology are compatible to the typical limitations of the hospital environment in which the tests are carried out. “Time is essential in the FFR research with newborns. On the one hand, because recording time limitations determine the stimuli they can record. On the other hand, for the actual conditions of the situation of newborns in hospitals, where there is a frequent and continuous access to the baby and the mother so they receive the required care and undergo evaluations and routine tests to rule out health problems,” authors add. Considering these restrictions, the responses of the 34 newborns that were part of the study were recorded in sessions that lasted between twenty and thirty minutes, almost half the time used in common sessions in studies on speech sound discrimination.

A potential biomarker of learning problems

After this study, the objective of the researchers is to characterize the development f neural encoding of the spectral and temporal fine structure of speech sounds over time. To do so, they are currently recording the frequency-following response in those babies that took part in the present study, who are now 21 months old. “Given that the two first years of life are a critical period of stimulation for language acquisition, this longitudinal evaluation of the development will enable us to have a global view on how these encoding skills mature over the first months of life,” note the researchers.

The aim is to confirm whether the observed alterations -after birth- in neural encoding of sounds are confirmed with the appearance of observable deficits in infant language development. If that happens, “that neural response could be certainly considered a useful biomarker in early detection of future literacy difficulties, just like detected alterations in newborns could predict the appearance of delays in language development. This is the objective of the ONA project, funded by the Spanish Ministry of Science and Innovation,” they conclude.

In a new study, “Modeling human migration under environmental change: a case study of the effect of sea level rise in Bangladesh,” researchers led by Maurizio Porfiri, an engineer at the Center for Urban Science and Progress (CUSP) at the NYU Tandon School of Engineering, apply data science to predict how the cascading effects of the migration in Bangladesh will ultimately affect 1.3 million people across the country by 2050. The work has implications for coastal populations worldwide.

The new study, co-authors of which include first author Pietro De Lellis, an engineer at the University of Naples Federico II, Italy, and Manuel Ruiz Marin, a mathematician at the Technical University of Cartagena, Spain, presents a mathematical model of human migration that considers not just economic factors but also human behavior — whether people are unwilling or unable to leave and if they later return home. It also considers the cascading effects of migration, as migrants repeatedly move to find new opportunities, and original inhabitants are displaced. The research is published in Earth’s Future, AGU’s journal for interdisciplinary research on the past, present and future of our planet and its inhabitants

“We are not only looking at a snapshot, but we are trying to reconstruct the trajectory of the migration and looking at its evolution,” said Porfiri, who is also an Institute Professor of mechanical and aerospace, biomedical, and civil and urban engineering at NYU Tandon.

According to the new model, the districts in the south along the Bay of Bengal will be the first to be impacted by sea-level rise, causing a migration that will ripple across the country and affect all 64 districts. Some migrants will likely be rejected by the existing residents — or displace them — triggering further migrations. While the population of the capital, Dhaka, initially will surge, the results suggest that movement away from the inundated capital region will ultimately cause its population to shrink.

Bangladesh is especially susceptible to sea-level rise because it is a low-lying country crisscrossed with rivers, and already experiences frequent flooding during the summer monsoon season. Its coastline on the Bay of Bengal measures about 580 kilometers (360 miles), with a large portion consumed by the Ganges river delta. An estimated 41 percent of its 163 million people live at elevations lower than 10 meters (about 32 feet).

The work follows upon a 2020 study by Porfiri and Ruiz Marin that examined population migrations in Bangladesh due to sea level rise as a way to verify an approach to detect spatial associations from small datasets, through the use of specific principles of information theory.

The authors emphasize that the new model can be used to study migration in response to any environmental disturbance that causes unrest, such as droughts, earthquakes or wildfires. Additionally, it is relatively simple and can make reliable predictions based on little data.

An earlier migration model using the same data predicted that the central region of Bangladesh, including its capital, Dhaka, would receive the greatest number of migrants. The new study agrees, but finds that the ripple effects from that migration will ultimately cause people to leave the capital, leading to a population decline.

Porfiri explained that the team’s approach to mathematical modeling for reliably predicting environmental migration in Bangladesh can be applied anywhere.

“Droughts, desertification, floods, earthquakes, and wildfire threaten livelihood worldwide; from wealthy to developing economies, every country is vulnerable to environmental change,” he said. “Mathematical models can assist in providing reliable predictions of environmental migration, which are critical for devising effective policy initiatives and improving our preparedness for future migration patterns.”

De Lellis added that the outputs from the model can help governments plan and prepare for the impacts of environmental disturbances by allocating resources to the most hard-hit regions and ensuring that cities are adequately equipped to deal with the influx of environmental migrants.

“Mathematical modeling is the only way we have to ground our future decisions,” said De Lellis. “Migration has lots of sources — [environmental disasters,] political tensions — but in the end, we need to use science to provide useful tools for decision-makers.”

The research is supported by the U.S. National Science Foundation (NSF), Groups of Excellence of the region of Murcia, the Fundación Séneca, Science and Technology Agency, and Compagnia di San Paolo, Istituto Banco di Napoli — Fondazione, project ACROSS.

Once land becomes established through dynamic processes like plate tectonics, it begins to weather and add crucial minerals and nutrients to the ocean. A record of these nutrients is preserved in the ancient rock record. Previous research used strontium isotopes in marine carbonates, but these rocks are usually scarce or altered in rocks older than 3 billion years.

Now, researchers are presenting a new approach to trace the first emergence of old rocks using a different mineral: “barite.”

Barite forms from a combination of sulfate coming from ocean water mixing with barium from hydrothermal vents. Barite holds a robust record of ocean chemistry within its structure, useful for reconstructing ancient environments. “The composition of the piece of barite we pick up in the field now that has been on Earth for three and a half billion years, is exactly the same as it was when it when it actually precipitated,” says Desiree Roerdink, a geochemist at University of Bergen, Norway, and team leader of the new research. “So in essence, it is really a great recorder to look at processes on the early Earth.”

Roerdink and her team tested six different deposits on three different continents, ranging from about 3.2 billion to 3.5 billion years old. They calculated the ratio of strontium isotopes in the barite, and from there, inferred the time where the weathered continental rock made its way to the ocean and incorporated itself into the barite. Based on the data captured in the barite, they found that weathering started about 3.7 billion years ago — about 500 million years earlier than previously thought.

“That is a huge time period,” Roerdink says. “It essentially has implications for the way that we think about how life evolved.” She added that scientists usually think about life starting in deep sea, hydrothermal settings, but the biosphere is complex. “We don’t really know if it is possible that life could have developed at the same time on land,” she noted, adding “but then that land has to be there.”

Lastly, the emergence of land says something about plate tectonics and the early emergence of a geodynamic Earth. “To get land, you need processes operating to form that continental crust, and form a crust that is chemically different from the oceanic crust,” Roerdink says.

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