The "window to the brain" is a transparent skull implant whose first studies go back to 2013 and that have led to an implant that is now usable to let a doctor interact with laser beams with the brain.
The basic idea is to instal a fixed implant in the skull letting laser beams to penetrate in the brain matter (using different ways of focalisation it is possible to have the light penetrate for a few mm in the brain, if deeper penetration is required an optical fibre has to be inserted).
Through optogenetics the doctor can condition specific neurones to react to the light beam letting possible to establish an effective therapy with a level of preciseness impossible so far.
The implant is made with the same material (yttria-stabilized zirconia) that is used in hip implants and in tooth implants (ceramics) manufactured in such a way to be transparent.
The team also demonstrated that an eventual infection of the implant (something that happens often with brain implants) can be cured using laser beams directly through the implant itself.