First images of dolphin brain circuitry hint at how they sense sound

By Carol Clark

Neuroscientists have for the first time mapped the sensory and motor systems in the brains of dolphins. Proceedings of the Royal Society B is publishing the results, showing that at least two areas of the dolphin brain are associated with the auditory system, unlike most mammals that primarily process sound in a single area.

“Dolphins are incredibly intelligent, social animals and yet very little is known about how their brains function, so they have remained relatively mysterious,” says Gregory Berns, a neuroscientist at Emory University and lead author of the study. “We now have the first picture of the entire dolphin brain and all of the white matter connections inside of it.”

The researchers applied a novel technique of diffusion tensor imaging (DTI) on the preserved brains of two dolphins who died after stranding on a beach in North Carolina more than a decade ago. The method for using DTI on a non-living brain was developed relatively recently and had previously only been used for research on deceased humans, primates and rats.

The study focused on the dolphin auditory system, since dolphins – along with several other animals, such as bats – use echolocation to sense their environments. “We found that there are probably multiple areas in the dolphin brain associated with auditory information, and the neural pathways look similar to those of a bat,” Berns says. “This is surprising because dolphins and bats are far apart on the evolutionary tree. They diverged tens of millions of years ago but their brains may have evolved similar mechanisms for using sound not just to hear, but to also create mental images.”

Dolphins emit clicks, squawks, whistles and burst-pulse sounds to communicate, navigate and hunt. Echolocation allows them to perceive objects by bouncing sound off surfaces.

“For decades, we’ve thought of the dolphin brain as having one primary auditory region,” says co-author Lori Marino, a neuroscientist specializing in the brains of dolphins, whales and other cetaceans. “This research shows that the dolphin brain is even more complex than we realized.” 

Formerly on the faculty at Emory, Marino is currently the executive director of the Kimmela Center for Animal Advocacy in Utah. Emory houses a number of preserved cetacean brains collected by Marino, via colleagues at the University of North Carolina, Wilmington, from stranding events. Various environmental agencies respond when dolphins and whales are beached, in an effort to save the animals and return them to the sea. If the animals die, parts of them may be preserved for use in scientific research.

The current study used the brains of a common dolphin and a pantropical dolphin from the Emory collection.

Previous investigations using magnetic resonance imaging (MRI) have revealed the complex anatomy of cetacean brains. But MRI scans only capture images of the brain’s basic structure. DTI focuses on the brain’s white matter, or the fiber pathways that connect neurons and different regions of the brain’s gray matter. DTI can detect the movement of water molecules along these fiber tracks.

The researchers used a special DTI technique for post-mortem brains developed by study co-authors Sean Foxley, Saad Jbabdi and Karla Miller at the University of Oxford. In a living, human brain, a DTI scan takes about 20 minutes. Scanning a post-mortem brain takes much longer, however, since it contains less water.

The dolphin brains posed a particular challenge since they are large – about the size of footballs – and had been preserved for years. They retained only small amounts of the water normally found in healthy tissue.

The researchers hypothesize that dolphins have more than one neural area associated with sound because they are using sound for different purposes.

“The signal was very weak, but it was there,” Berns says. “Each of the specimens required nearly 12 hours of scanning.” The data from the DTI scans allowed the researchers to map out the white matter pathways, essentially the wiring diagram for the dolphin brain, in high detail.

The results show that the dolphin auditory nerve enters the brain stem region and connects both to the temporal lobe (the auditory region of many terrestrial mammals) and to another part of the brain near the apex known as the primary visual region. The researchers hypothesize that dolphins have more than one neural area associated with sound because they are using sound for different purposes.

Dolphins emit clicks, squawks, whistles and burst-pulse sounds to communicate, navigate and hunt. Echolocation allows them to perceive objects by bouncing sound off surfaces.

“Dolphins are the most sophisticated users of biological sonar in the animal kingdom,” Marino says. “They can find fish hidden from sight in sand with ease.”

Experiments have shown that dolphins can echolocate on a hidden, complex 3-D shape and then pick out that shape by sight. “They can rapidly move back and forth between their senses of sight and sound,” Marino says. One dolphin’s echolocation signals and echoes may be picked up by another dolphin, she adds. “They have a complex communication system and a unique ability to emit different types of sounds, like a click and a whistle, simultaneously.”

The researchers hope that their map of dolphin neural circuitry will help unlock secrets of the dolphin mind, including how they communicate and perceive their environment.

“Our study was the first to use this DTI technique on a dolphin brain, and on a specimen that was more than a decade old,” Berns says. “Our success opens up the possibility of using this tool to study the archived brains of all sorts of amazing animals in museum collections around the world.”

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The math of shark skin

July is shark month at Emory. We’re celebrating the science surrounding our fascination with sharks – creatures that have evolved extraordinary abilities during 450 million years of swimming in the oceans.

By Carol Clark

“Sharks are almost perfectly evolved animals. We can learn a lot from studying them,” says Emory mathematician Alessandro Veneziani.

As an expert in fluid dynamics, Veneziani is particularly interested in the skin of sharks, which is not smooth – as might be expected for such a streamlined, efficient swimmer – but irregular and rough. “It’s counterintuitive,” Veneziani says. “One would expect that smooth skin would make a shark faster in the water but it’s not true, and there is a mathematical reason.”

The ridges, or riblets, on shark skin break up vortexes of water and reduce drag, a phenomena known as the riblet effect. Using differential equations, mathematicians have duplicated this effect so it can be applied to industry. Aircraft, for instance, are painted with special finishes to create a riblet effect.

Veneziani once worked on a project for a European swimwear company. They used the math of shark skin to create swimsuit fabric for competitive swimmers. Tests showed that these swimsuits could significantly reduce drag in the water, to the point that they were banned from the Olympics in 2008.

“In the Olympics, you are not allowed to swim like a shark,” Veneziani says.

The time spent studying the math of shark skin was not wasted effort for Veneziani. He now applies similar principles of fluid dynamics to study how blood flows through human arteries. His lab creates computer simulations to help doctors decide on the best course of action for patients with cardiovascular disease.

“One of the great things about mathematics is that you can gain experience in one specialty, like shark skin, and use it in a completely different area, like blood dynamics,” Veneziani says. “Math is the common language of nature.”

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Calving icebergs fall back, spring forward, causing glacial earthquakes

"We've provided an unprecedented understanding of how a glacial earthquake evolves," says Emory physicist Justin Burton. The research focused on Helheim Glacier in Greenland, above. Photo by NASA/Jim Yungel.

By Carol Clark

When a massive iceberg breaks off from the front of a glacier it can fall backwards, slamming into the glacier with such force that it reverses the ice flow for several minutes and causes it to drop, producing an earthquake that can be measured across the globe.

The journal Science is publishing the discovery, including detailed documentation of the forces involved in these iceberg calving events and an explanation for the causes of glacial earthquakes. The research marks a major step toward the ability to measure the size of iceberg calving events in near real-time and from anywhere in the world.

“Glaciers are extremely sensitive indicators of climate change,” says co-author Justin Burton, a physicist at Emory University who specializes in laboratory modeling of glacial forces. “Having a quantitative understanding of how our polar regions are losing ice is crucial to any forecasting related to climate change, in particular sea-level rise and its environmental and economic impacts.”

Placing a GPS sensor. (Swansea)

The study, which focused on Helheim Glacier in the Greenland Ice Sheet, also included scientists from the universities of Swansea, Newcastle and Sheffield in the UK and the universities of Columbia and Michigan in the U.S.

The Greenland Ice Sheet is disappearing at a faster rate than Antarctica, and shows no sign of slowing down. As much as half of that loss is due not to melting, but to icebergs breaking off and discharging into the sea, a process known as calving. As sheets of ice taller than a New York skyscraper fall over and collapse into the water they release energy equivalent to several nuclear bombs.

In 2003, scientists discovered the existence of glacial earthquakes. They knew that iceberg calving caused these quakes, but it was unclear why. A regular earthquake originates from stress building up from deep within the Earth, which then gets released suddenly. A glacial earthquake, however, originates on the surface and happens in relative slow motion, during the 10 to 15 minutes it takes an iceberg to flip 90 degrees, collapse into the sea and generate waves of energy.

The study authors wanted to gain a better understanding of the processes involved in collapsing icebergs and how they cause glacial earthquakes.

Tavi Murray, a glaciologist from Swansea University, led the field portion of the study. During the summer of 2013, researchers from Swansea, Newcastle and Sheffield universities flew over Helheim Glacier in helicopters. They installed a sophisticated network of Global Positioning System (GPS) devices on the glacier’s surface to record movements of the glacier in the minutes surrounding calving events.

The Greenland Ice Sheet is getting smaller. If it melts entirely, scientists estimate that sea level will rise about 6 meters (20 feet). Photo of Helheim Glacier by Nick Selmes, Swansea University.

One of the surprises revealed by the resulting data was that some of the calving events actually reversed the flow of the glacier during a glacial earthquake.

“That’s really strange,” Burton says, “because a glacier is an enormous mass that is always moving towards the sea. What could possibly reverse that?”

Burton led a laboratory modeling portion of the study, along with Mac Cathles, who is now at the University of Michigan. They built a rectangular, Plexiglas water tank as a scaled-down version of a fjord. Rectangular plastic blocks that have the same density as icebergs are tipped in the water tank and the resulting hydrodynamics are recorded.

The analysis phase also drew from the expertise of co-author Meredith Nettles, a seismologist at Columbia’s Lamont-Doherty Earth Observatory, and data in the Global Seismographic Network. The collaborative analyses and experimental modeling allowed the researchers to tease apart all the forces responsible for the motion of the glacier, recreate them in the lab, and solve the mystery of how glacial earthquakes work.

Watch a video of the Burton lab's model of a backwards falling iceberg, based on the data from Helheim Glacier:


“We were able to explain the motion of the GPS sensors by tracking all the forces that affect the glacier during iceberg calving, providing an unprecedented understanding of how a glacial earthquake evolves,” Burton says.

They found that many of the calving icebergs are falling backwards, slamming into the face of the glacier before they collapse into the sea. The front of the glacier gets compressed like a spring, temporarily reversing the motion of the glacier and generating the horizontal force of a glacial earthquake.

As the iceberg hits the water, it rapidly reduces pressure behind the rotating iceberg. This dramatic drop in water pressure draws the glacier down about 10 centimeters, while pulling the Earth upwards, creating the vertical force seen in the seismic signature of a glacier earthquake.

“This research required the combined efforts of glaciology, seismology and physics,” Burton says. “It was great to work hand-in-hand with field researchers, while also showing that lab research is crucial to understanding what’s happening on the surface of the Earth.”

Glacial earthquakes are globally detectable seismic events. The researchers hope their detailed documentation of the forces at play will help interpret the remote sensing of calving events, which are increasingly occurring at tidewater-terminating glaciers in Greenland and Antarctica.

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How flu viruses use transportation networks in the U.S.

Emory biologists analyzed transportation data and flu cases from across the United States. The graphic of the U.S. interstate commuter network shows the number of people traveling daily between states for work. Credit: Brooke Bozick.

By Carol Clark

To predict how a seasonal influenza epidemic will spread across the United States, one should focus more on the mobility of people than on their geographic proximity, a new study suggests.

PLOS Pathogens published the analysis of transportation data and flu cases conducted by Emory University biologists. Their results mark the first time genetic patterns for the spread of flu have been detected at the scale of the continental United States.

“We found that the spread of a flu epidemic is somewhat predictable by looking at transportation data, especially ground commuter networks and H1N1,” says Brooke Bozick, who led the study as a graduate student in Emory’s Population Biology, Ecology and Evolution program. “Finding these kinds of patterns is the first step in being able to develop targeted surveillance and control strategies.”

The co-author of the study is Leslie Real, Emory professor of biology and Bozick’s PhD adviser.

One of the fundamental ideas in ecology is isolation by distance: The further apart things are geographically, the more distant they tend to be genetically.

This idea applies to disease ecology in the cases of animals that do not travel far from where they are born. Rabies spread by raccoons, for instance, tends to generate a wave-like pattern of transmission across a geographic space.

People, however, are much more mobile, often traveling by rail, road and air. The human mobility effect of an epidemic stands out starkly on the global scale. For instance, during the 2003 outbreak of severe acute respiratory syndrome (SARS), airline travel clearly connected cases in people from Asia and Canada.

Map shows an example of how commuting communities can differ from state boundaries. Credit: Brooke Bozick.

The researchers wanted to see if they could detect a correlation to mobility and the genetic structure of seasonal flu cases on a national scale for the United States.

The study tapped Genbank, an online, public repository of genetic flu data, to analyze U.S. cases from 2003 to 2013 for two different subtypes of seasonal flu: H3N2 and H1N1. Transportation data for that decade was drawn from the U.S. Census Bureau and the Bureau of Transportation Statistics, to map out networks of air travel and ground commutes, and the number of people moving along them during the flu season.

The researchers compared genetic distance of the flu subtypes with their geographic distance and the measures of distance defined by airline and commuter transportation networks.

They found some correlations in both subtypes for all the distance metrics used. The correlations were seen a greater proportion of the time, however, when looking at commuter movements and the H1N1 subtype.

“H1N1 tends to be a milder subtype of flu that spreads slower, so that may make it easier to pick up the pattern across shorter-distance commutes,” Bozick says. “We think that a similar pattern for H3N2 may exist. The pattern may just be harder to detect, since H3N2 tends to be more virulent and spread faster, from coast-to-coast.”

The study shows that there are underlying spatial patterns in the genetic data, and that they are dependent on how the “distance” between locations is being measured, she adds.

“Humans can move long distances very rapidly so the idea that geographic proximity is key to determining disease spread doesn’t always hold,” Bozick says. “The patterns we found are likely influenced by states with many commuters, and the identification of these states, as well as network pathways that contribute substantially to influenza spread, is an important next step for epidemiological research.”

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Dengue mosquitos hitch rides on Amazon river boats
Human mobility data may help curb epidemics

Dengue mosquitos hitch rides on Amazon river boats

Boats are the main means of transport in the Peruvian Amazon. Some of these boats are providing a first-class ride for disease-carrying mosquitos, helping them expand their range, a study found.

By Carol Clark

The urban mosquito that carries the dengue fever virus is hitching rides on river boats connecting the Amazonian town of Iquitos, Peru, with rural areas.

PLOS Neglected Tropical Diseases published a study by disease ecologists at Emory University, showing how the Aedes aegypti mosquito, which is normally associated with urban areas, is tapping human transportation networks to expand its range.

“The majority of large barges we surveyed were heavily infested,” says Sarah Anne Guagliardo, who led the study as a PhD student in the lab of Uriel Kitron, chair of Emory’s Department of Environmental Sciences. “As the barges move across the Peruvian Amazon they are carrying large populations of these mosquitos, which can transmit many viral diseases, the most important of which is dengue fever.”

Like the housefly, Aedes aegypti is perfectly adapted to the domestic life of humans. It especially thrives in densely populated urban areas, since it feeds almost exclusively on human blood and has a limited flight range of about 100 meters.

“When Aedes aegpti mosquitos began popping up in rural areas around Iquitos, we knew that humans must somehow be involved in that transportation process,” Guagliardo says.

The research team boards a large cargo barge, on left, to survey for mosquitos. (Photo courtesy Sarah Anne Guagliardo.)

Iquitos, located deep in the Amazonian rainforest, is one of the most isolated cities in the world, accessible only by boat or plane, except for one two-lane road connecting it to a much smaller town. The population of 400,000 is surrounded by thick jungle that is difficult to clear, inhibiting urban expansion.

To learn how the mosquitos of Iquitos hitch rides with humans, the researchers investigated six different vehicle types, from large and medium-sized barges, water taxis and speedboats to buses and road taxis.

Large barges (71.9 percent infested) and medium barges (39 percent infested) accounted for most of the infestations. In contrast, buses had an overall infestation rate of 12.5 percent.

The cargo hold of large barges, where water often collects in puddles, was ground zero for the infestations. “We were collecting not just adult mosquitos, but also pupae, larvae and eggs,” Guagliardo says. “The mosquitoes are not just riding the boats, they are reproducing on the boats.”

These large barges, which can be about 60 meters long, may have as many as four floors in addition to the cargo hold. They carry human passengers along with livestock, plantains, fish, gasoline and other goods. The medium barges tend to be half the size and lack cargo holds.

Many of the cargo barges are old and not well-maintained.

The researchers surveyed for mosquitos using the Prokopack aspirator, a mosquito “vacuum” co-invented by Emory disease ecologist Gonzalo Vazquez-Prokopec.

“The cargo hold is in the bottom of the large barges and you have to crawl into really dark spaces to collect mosquitos,” Guagliardo says. “There’s often rotting organic matter from things like plantains and fish. And it’s moldy and damp. Many of the barges are really old and rust holes form on each floor and ceiling. Every time it rains, water drips down and collects in the cargo hold.”

It’s a first-class ride, however, for these disease-carrying mosquitos. The adults have a dark, cool resting place, while their eggs and larvae can incubate in standing puddles. If the mosquitoes get hungry, a captive group of human hosts is nearby for blood meals.

“I think it’s important that people are aware that this is a problem,” Guagliardo says. “Our study is the first of its kind, to my knowledge, comparing mosquito infestations across a range of vehicles. I’m curious how these mosquitos may use modes of transport in other parts of the world.”

Some of the large barges of Iquitos with infestations of adult and immature mosquitoes were surveyed repeatedly by the research team during different seasons of the year. “It turns out the barges that were infested were consistently infested, and that a small proportion of barges produce the vast majority of mosquitos,” Guagliardo says. “That suggests that some boats may act as super-transporters of mosquitos, just as individual human hosts may act as super-spreaders of pathogens.”

The researchers propose that governmental agencies invest in mosquito control programs for aquatic transport, and implement more stringent punitive policies and incentives to ensure the cooperation of boat owners. The programs could target those boats producing the greatest amount of mosquitoes.

During the last 50 years, the incidence of dengue, which causes debilitating pain and can be fatal, has increased 30-fold. The World Health Organization estimates that 50-100 million dengue infections occur each year.

Guagliardo, who received her PhD from Emory in May, currently works on HIV/AIDS programs for the Centers for Disease Control and Prevention.

In addition to Guagliardo, Kitron and Vazquez-Prokopec, the study’s authors include Amy Morrison, Jose Luis Barboza, Edwin Requena and Helvio Astete.

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Credit: Top and bottom photos from ThinkstockPhotos