Radiation from the 2011 disaster at the Fukushima Daiichi nuclear power plant contaminates most Japanese seafood at low levels, researchers estimate February 29 in the Proceedings of the National Academy of Sciences.

For aquatic foods, data on lingering concentrations of cesium is limited in terms of the number of species sampled and the levels that surveys can even detect. To fill in the blanks, a team of researchers in Japan drew from survey measurements from April 2011 to September 2015 and devised a way to predict cesium contamination in different aquatic species across Japan.

The analysis provides mixed news: Overall, cesium contamination is pretty low. But, some species retain higher levels than others. Larger fish near the top of the food web tended to have the highest levels of contamination. The researchers predict that such factors put some wild freshwater species like the whitespotted char (Salvelinus leucomaenis leucomaenis) and the Japanese eel (Anguilla japonica) at higher risk for contamination.

Once every 69 years, a nearby star dramatically dims for about three and a half years during the longest known stellar eclipse in our galaxy.

The star, called TYC 2505-672-1, is a red giant, about 10,000 light-years away in the constellation Leo Minor. The star is orbited by a dim, hot companion star that appears to be enveloped by a thick cloud of dust roughly one to three times as wide as Earth’s orbit. The cloud, reported in an upcoming Astronomical Journal, blocks much of the red star’s light from reaching Earth for a good long time.

Researchers already knew that TYC 2505-672-1 had drastically faded recently. But astronomer Joseph Rodriguez of Vanderbilt University in Nashville and colleagues scoured data from many telescopes — including a Harvard University photograph archive dating back to 1890 — and found that the starlight dipped and rebounded not only between 2011 and 2015 but also in the 1940s. The previous eclipse record holder was Epsilon Aurigae, a star 2,000 light-years away that dims for about 24 months every 27 years.

Editor’s Note: This story was updated on April 27, 2016, to correct distances and the name of the previous eclipse record holder.

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.

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.

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.