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A team of researchers has built an AI system that can look at a brain scan and reconstruct, with notable accuracy, the image a person was viewing when it was taken. Run the process backward, and the same tool can predict how someone's brain will respond to a given picture before they've even seen the full scan analyzed. That two-way trick is the headline item in today's edition of The Download, MIT Technology Review's weekday rundown on tech news.

The appeal is obvious. Scientists studying the brain get a new window into how visual processing actually works, and people who are locked-in, unable to speak or move, might eventually use something like this to communicate. There's even talk of reconstructing dreams. But the same capability that makes this useful also makes it unsettling: a method that can pull images out of someone's head doesn't need much tweaking before it's pulling out thoughts that were never meant to be shared, raising obvious consent problems.

Also in this edition: the Pentagon has brought Elon Musk on to help lead a project focused on future warfare, and a look at how small, unconventional batteries, tucked into things like induction stovetops and food carts, are finding a role in the grid that giant installations can't always fill.