I read an article around four years ago about how electrodes are clumsy devices, but scientists had succeeded in making neurons which can be controlled by coupling the signal activation proteins in some clever way to an artificially inserted light-sensitive gene, and then using optic fibres or lasers to get single-neuron fidelity control. This technology is already yielding major insights into brain function (not to mention the colossal significance that this will have for the future of humanity and technology), along with rapid advances in brain imaging and other areas. Here are a few articles I found about the new breakthroughs. Please add more.

Orthogonal axons

Physical memory manipulation

Retina code