Decoding Brain Activity with AI

This is Star Trek-level technology:

In a scientific first, Columbia neuroengineers have created a system that translates thought into intelligible, recognizable speech. By monitoring someone’s brain activity, the technology can reconstruct the words a person hears with unprecedented clarity. 

Engineers translate brain signals directly into speech

This was done by tracking the brain activity created by someone listening to very simple words (the numbers 0-9), not imagining speaking those words. But it’s impressive it could be done at all using only brain signals, and it suggests that it is indeed possible to think a sentence and have a machine say it out loud.

Open questions: Would a neural network trained on one person work on many others? What kinds of other thoughts might be decoded?