Using an electronic system that duplicates the neural signals associated with memory, they managed to replicate the brain function in rats associated with long-term learned behavior, even when the rats had been drugged to forget.
This series of experiments, as described, sounds very well-constructed and thorough. The scientists first recorded specific activity in the hippocampus, where short-term memory becomes long-term memory. They then used drugs to inhibit that activity, preventing the formation of and access to long-term memory. Using the information they had gathered about the hippocampus activity, they constructed an artificial replacement and implanted it into the rats' brains. This successfully restored the rats' ability to store and use long-term memory. Further, they implanted the device into rats without suppressed hippocampal activity, and demonstrated increased memory abilities in those subjects.
"These integrated experimental modeling studies show for the first time that with sufficient information about the neural coding of memories, a neural prosthesis capable of real-time identification and manipulation of the encoding process can restore and even enhance cognitive mnemonic processes," says the paper.
It's a truly impressive result.