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The hand traces the word "mom" in the air — familiar arcs and strokes. The brain, meanwhile, is not flipping through a photo of each letter. It launches a chain of simple movements. Neuroengineers put this idea to the test: imagined handwriting is not a gallery of ready-made pictures but a construction set built from the same motor "bricks."

In the experiment, volunteers received intracortical implants — tiny sensors placed directly in the brain. They mentally wrote Latin letters. The computer recorded not the letters themselves but the patterns of electrical activity associated with individual strokes: a loop, a straight line, a hook. Then the subjects were shown unfamiliar characters, and the algorithm tried to guess what they were "writing." The result: in three out of five attempts, the machine found the correct character among thousands, never having seen it before.

This is like a translator who does not memorize every word of a foreign language but learns roots and prefixes. Encountering an unfamiliar word, they piece together its meaning from familiar parts. Similarly, the neural interface stores a dozen motor "syllables" instead of thousands of letter images and combines them on the fly. For a person with paralysis, this means no need to spend hours calibrating the system for each new symbol: you only have to "explain" the basic movements once.

The discovery changes our view of the motor cortex — the brain region that commands movement. It thinks not in ready-made postures but in building blocks. When we doodle in the margins of a notebook, the skull is assembling from universal parts — the very ones that once helped our ancestors carve the first drawing on stone.