Gridiron risks

The evidence that football can cause long-term brain injuries continues to pile up. Boston University researchers who studied the brains of 376 deceased ­former NFL players found that 92 ­percent had chronic traumatic encephalopathy (CTE), a degenerative brain disorder, according to a February announcement. By comparison, a 2018 Boston University study that included people from the general population identified CTE in only 1 of the 164 participants.

The condition, which can only be identified after death, is characterized by tissue degeneration and abnormal protein deposits in the brain. CTE onset is linked to repeated head impact. It can take years or decades for a person with CTE to experience noticeable symptoms. Early signs can include trouble concentrating, short-term memory loss, and severe mood swings. As the disease progresses, cognition problems and memory loss worsen, sometimes leading to dementia.

The researchers cautioned that their use of brain bank data introduced a bias toward a subset of people most affected by CTE. Thus, the true incidence of CTE in active and retired NFL players may not be equivalent to what the researchers found.

The shape of water

Scientists in England have discovered a bizarre new form of ice they call “medium-density amorphous ice,” created by shaking ice together with steel balls at very low temperatures. Unlike typical solid ice that floats in water, the novel ice has the same density as liquid water. And while solid ice has an organized molecular structure, the novel ice’s molecules are joined haphazardly, according to the researchers’ study, published Feb. 2 in Science. —H.F.

Underwater awareness

A new study from researchers at Osaka Metropolitan University suggests that a species of fish known for its rare ability to perceive itself in a mirror does so by memorizing its own face.

In the study, several cleaner wrasses—which tend to attack unfamiliar fish—were each presented with a series of photos: itself, an unfamiliar cleaner, its own face pasted onto an unfamiliar cleaner’s body, and an unfamiliar cleaner’s face pasted onto its own body. The fish only attacked the two photos with unfamiliar cleaners’ faces.

A second experiment drove home the point: After viewing photos of themselves with a parasite-like mark on their throats, six out of eight cleaners tried to remove the mark on their own throats. But the fish didn’t try to remove the mark when shown photographs of other fish with the marking. The study was published Feb. 6 in Proceedings of the National Academy of Sciences. —H.F.