A brain scan (artificially coloured) produced by magnetic resonance imaging. Credit: K H Fung/Science Photo LibraryA brain implant can decode a person’s internal chatter — but the device works only if the user thinks of a preset password1.The mind-reading device, or brain–computer interface (BCI), accurately deciphered up to 74% of imagined sentences. The system began decoding users’ internal speech — the silent dialogue in people’s minds — only when they thought of a specific keyword. This ensu...