Moumita Das

The brain doesn't just react to the world: it's constantly guessing what will happen next. This principle is called predictive coding: neurons compare expectations with reality and update their internal picture when an error occurs. But how such a complex system could be wired into the living tissue of the cortex remained unclear.

A crystal the size of a fingernail sits between the plates of a capacitor. A magnetic field is switched on, and the crystal stretches like a ribbon pulled at both ends: its length increases by 60, or even 120, percent. This is not a typo. Ordinary iron in a magnetic field changes its length by millionths of a percent, whereas here the change is large enough to see with the naked eye.