NEW YORK — Cells in a brain structure known as the hippocampus are known to be cartographers, drawing mental maps of physical space. But new studies show that this seahorse-shaped hook of neural tissue can also keep track of social space, auditory space and even time, deftly mapping these various types of information into their proper places.

“The hippocampus is an organizer,” says neuroscientist Howard Eichenbaum of Boston University.

Neuroscientist Rita Tavares described details of one of these new maps April 2 at the annual meeting of the Cognitive Neuroscience Society. Brain scans had previously revealed that activity in the hippocampus was linked to movement through social space. In an experiment reported last year in Neuron, people went on a virtual quest to find a house and job by interacting with a cast of characters. Through these social interactions, the participants formed opinions about how much power each character held, and how kindly they felt toward him or her. These judgments put each character in a position on a “social space” map. Activity in the hippocampus was related to this social mapmaking, Tavares and colleagues found.
It turns out that this social map depends on the traits of the person who is drawing it, says Tavares, of Icahn School of Medicine at Mount Sinai in New York City. People with more social anxiety tended to give more power to characters they interacted with. What’s more, these people’s social space maps were smaller overall, suggesting that they explored social space less, Tavares says. Tying these behavioral traits to the hippocampus may lead to a greater understanding of social behavior — and how this social mapping may go awry in psychiatric conditions, Tavares said.

The work emphasizes that the hippocampus is not just a mapper of space, Tavares says. Instead, it is a mapper of relationships. “It’s relational learning,” she says. “It’s everything in perspective.”

Other research, discussed at a meeting in February, revealed a role for the hippocampus in building a very different sort of map — a map of sounds. Stationary rats were trained to “move” through a soundscape of different tones, pushing a joystick to change the sounds to reach the sweet spot — the target tone. As the rats navigated this auditory world, nerve cells in their hippocampus were active in a way that formed a map, Princeton University neuroscientist Dmitriy Aronov reported in Salt Lake City at the annual Computational and Systems Neuroscience meeting.

Cells in the hippocampus can also map time, keeping count as seconds tick by, Eichenbaum has found (SN: 12/12/15, p. 12). All of these types of information are quite different, but Eichenbaum argues that they can all be thought of as memories — another mental arena in which the hippocampus plays an important role. Organizing these memories into a sensible structure may be the big-picture job description of the hippocampus, he says. “What’s being tapped in all of these studies is that we are looking at a framework, whether it’s a physical spatial framework, a social space framework, a pitch framework, or a time framework,” Eichenbaum says.

Ocean outlook
Earth’s oceans are a hot mess. They absorb heat at twice the rate that they did nearly 20 years ago, Thomas Sumner reported in “Ocean heating doubles” (SN: 2/20/16, p. 18). Meanwhile, phytoplankton release more heat during photosynthesis than previously thought, Chris Samoray reported in “Ocean flora flunk photosynthesis test” (SN: 2/20/16, p. 12). And the trillions of plastic particles littering the oceans are creating new habitats for microbes with unknown consequences, Samoray wrote in “Floating fortress of microbes” (SN: 2/20/16, p. 20).
Anna Carter wondered if these findings are connected. “Is it possible that phytoplankton are contributing to ocean warming?” Carter asked. “How might the organisms now collecting on all the plastic in the ocean be related?”

Heat produced by phytoplankton doesn’t have a large impact on ocean temperature, says Sumner. “The phytoplankton are catching sunlight that otherwise could warm the water,” he wrote. “Another thing to keep in mind is that the oceans are colossal. At its deepest, the Pacific Ocean is about as deep as the cruising altitude at which most commercial airliners fly. Phytoplankton live in the top sliver of the water column, so any effect they have will be minuscule compared with the size of the ocean.” As for plastic-dwelling microbes, there is still so much to discover, Samoray says. Their contribution to ocean warming is currently unknown.

Ants on the move
Florida harvester ants may be the Frank Lloyd Wrights of the animal kingdom. They construct intricate and mysterious nests, Susan Milius reported in “Restless architects we don’t understand” (SN: 2/20/16, p. 4). Researchers investigated why ants frequently build and abandon elaborate nests, and scatter charcoal around nest openings.

Readers had their own ideas about the unusual behavior. “[Charcoal] is an effective absorber of organics. Is it possibly used for absorbing their scent as a protective measure against predators?” Mark Ayers asked.

Walter Tschinkel, the Florida State University scientist featured in the story, says that the scorched plant matter ants use may not be as effective for these purposes as commercial charcoal. Field tests found no sign that charcoal would deter attacks by other ants.

Reader Joe De Vita speculated that colonies abandon their nests because of waste buildup. Tschinkel notes that this hypothesis has yet to be tested. “Digging up the vacated nest often reveals chambers with matted, blackened floors, presumably from fungus and other microorganisms, but whether this condition has any negative (or for that matter, positive) effects on harvester ants is unknown,” he says. An experiment to test this hypothesis is possible, but “ain’t all that easy. Still, stay tuned.”

Milk for spills
Researchers have created a fibrous membrane made from milk proteins and carbon that could filter toxic heavy metals from severely polluted waters, Sarah Schwartz reported in “Altered milk protein cleans up pollution” (SN: 2/20/16, p. 14). In lab tests, the membrane removed over 99.9 percent of lead from a contaminated solution.

“It is a very exciting method,” wrote Janece Von Allmen. “Has anyone thought to test this method in the real polluted waters of Flint, Michigan?”

The filters are still in an early stage of design, Schwartz says. The membranes work in the laboratory to capture heavy metals and radioactive particles, but testing in the real world is a must. “Bodies of contaminated water are most likely chemically different from lab-made lead solutions and could change the membrane’s performance,” she says.

Whether or not these membranes would work in the Flint River is unclear because the river is not the original source of lead. The toxic heavy metal accumulates as the water passes through corroding pipes. The good news is the prototype shows signs of being efficient and is relatively cheap to produce.

In a bit of Irish luck, archaeologists have found evidence of the Emerald Isle’s earliest known humans. A brown bear’s kneecap excavated in 1903, featuring stone tool incisions, pushes back the date that humans set foot in Ireland by as many as 2,500 years.

Radiocarbon dating at two independent labs places the bone’s age between about 12,800 and 12,600 years old, say Marion Dowd of the Institute of Technology, Sligo in Ireland and Ruth Carden of the National Museum of Ireland in Dublin. Melting glaciers and milder temperatures in northwestern Europe at that time made it easier for humans to reach Ireland by boat to hunt game, at least for several weeks at a time, the researchers propose in the May 1 Quaternary Science Reviews.
Until now, the oldest signs of people on Ireland came from a hunter-gatherer camp dating to about 10,290 years ago.

Carden discovered the brown bear’s kneecap while studying bones that had been packed away in boxes in the 1920s, after the bones’ 1903 discovery at Ireland’s Alice and Gwendoline Cave.

Interviewing for a new job is filled with uncertainty, and that uncertainty fuels stress. There’s the uncertainty associated with preparing for the interview — what questions will they ask me? What should I put in my portfolio? And then there’s the ambiguity when you’re left to stew. Did I get the job? Or did someone else?

Scientists have recently shown that these two types of uncertainty — the kind we can prepare for, and the kind we’re just stuck with — are not created equal. The uncertainty we can’t do anything about is more stressful than the one we can. The results help show exactly what in our lives freaks us out — and why. But the findings also show a positive side to the stress we feel when not knowing what’s ahead — the closer our stress levels reflect the real ambiguity in the world, the better we perform in it.

“There is a bias in the public perception” against stress, says Claus Lamm, a cognitive neuroscientist at the University of Vienna in Austria. But stress “prepares us to deal with environmental challenges,” he notes, preparing us to fight or flee, and it keeps us paying attention to our surroundings.

For decades, scientists have been trying to figure out just what makes us stressed and why. It turns out that unpredictability is a great stressor. Studies in the 1960s and 1970s showed that rats and humans who can’t predict a negative effect (such as a small shock) end up more frazzled than those who can predict when a zap is coming. In a 2006 study, people zapped with unpredictable electric shocks to the hand rated the pain as more unpleasant than when they knew what to expect.

What is going on in the brain when judging the uncertainty of a situation and translating it to stress? Lamm and his group recently sought the answer to answer this question by combining measures of electrical activity in the brain (via electroencephalogram) with functional magnetic resonance imaging to show blood flow patterns in 25 participants getting rounds of shocks on their hands. A visual cue told the participants what to expect — sort of. Sometimes the participant knew with 100 percent certainty that either a painful shock or nothing at all was coming. Sometimes there was only 50 percent certainty. No matter what, the shock would happen (or not) in the next 15 seconds, leaving the people in the scanner with nothing to do but wait.

During that waiting period, the brain prepares for a shock in different ways, depending on whether the jolt is certain or uncertain, Lamm and his colleagues reported last February in Human Brain Mapping. During the first two seconds, the brain is processing the visual cue. “You have an initial quick evaluation,” Lamm explains, categorizing whether the stimulus is going to be aversive and whether it is certain or uncertain. If the possibility for a zap was ambiguous, there was a quick increase in blood flow to participants’ visual processing areas. This suggests the brain is getting ready to take in more information and pay more attention — to get a better read on if that shock is really coming or not.

If the zap is definitely going to happen, the last two seconds before delivery saw increased activity in the posterior insula. The insula participates in processing someone’s current state, including pain processing and emotional awareness — “basically reading out the physiological signals of your body,” Lamm says. Pain is coming, brace yourself.
When participants weren’t sure if the shock was coming, the last two seconds of waiting were accompanied by increased brain activity in areas related to sensing the environment and maintaining attention — such as the parietal lobe, orbitofrontal cortex and angular gyrus. The brain was on high alert, continuing to look for any information that could determine when and if the pain would arrive.

But this is only one kind of stress —and one kind of uncertainty. “We know a lot about what happens if you take someone and give them a stressful experience,” says Archy de Berker, a neuroscientist at University College London. “But in a way, that approach is missing out on a whole step: What is it about the experience that makes it stressful?” Is it the ambiguity? Or is it the shock to the hand? Is it both?

But there’s also more than one kind of ambiguity to prepare for. Remember the job interview scenario: You can reduce some of the uncertainty by preparing for your interview. But once the interview has passed, you’re stuck with irreducible uncertainty — that endless wait for the call that may never come.

To separate out these two forms of uncertainty, de Berker recruited 45 participants for a different hand-shock experiment. For each trial, the participant was presented with one of two rocks and asked if there was a snake under it. At first, the snake might be under rock “A” 100 percent of the time. Then it might change, and the snake might be under rock “A” only 60 percent of the time, spending the rest of the time under rock “B.” For some trials, the participant could easily learn to predict where the snake would be, while for others the rock-turner was always uncertain. But one thing remained certain: If they saw the snake, they’d get a shock, even if they predicted the outcome correctly.

As the participants played this painful game, de Berker and his colleagues monitored their skin conductance and pupil size — measures of physical stress. They also asked the participants how stressed out they felt.

The amount of ambiguity the participants had about whether the snake was under the rock was associated with their stress. If they could easily predict when the shock would come, reducing their uncertainty, they shocks were easier to take. But if the outcome remained difficult to predict — if no amount of learning was going to help — the participants were much more stressed out.

But if the participants had a good feel for just how uncertain the odds were — if their measures of stress tracked well with the amount of ambiguity — they ended up with an unexpected benefit: They performed better on the rock and snake task (though they still got shocked for their pains). The scientists published their results March 29 in Nature Communications.

The study “reveals more quantitatively how stress (both self-reported and measured with physiological arousal) is driven by… ‘irreducible uncertainty,’ uncertainty about the state of the world that we can’t control,” says Ross Otto, a neuroscientist at New York University. It’s that irreducible uncertainty — the fact that the job applicant just doesn’t know if he’s got the job until the call comes through, and there’s nothing he can do about it — that really gets to us.

But the part of the stress we can control represents the positive side of an unpleasant feeling. “We always tend to think of stress as a negative effect, you don’t want to be stressed,” Lamm says. “But in the end, if you’re not stressed you will not perform. You need a certain level of arousal to meet challenges.”

There’s no known mad plant disease. But prions — which show their dark side in mad cow disease — may occur in plants as a form of memory.

Prions are proteins that change shape and shift tasks, and then trigger other proteins to make the same change. Inheriting prions lets cells “remember” and replicate that shift in form and function. Now a protein called luminidependens, which is connected with flowering, shows signs of these shapeshifter and template powers, researchers report April 25 in the Proceedings of the National Academy of Sciences.

Study coauthor Susan Lindquist of the Whitehead Institute for Biomedical Research in Cambridge, Mass., and her colleagues devised a way to test plant proteins for prion power by swapping bits of them into yeast prions. Luminidependens, found in the common lab plant Arabidopsis thaliana, fit the criteria, and may be the first botanical protein shown to act like a prion. Prionlike memory might be useful in such floral tasks as keeping track of a decent winter’s chill.