Amazing episode in all regards. It revealed a lot of clues about the past and the present:

• It appears that Gemma was scouted for the Lumon experiments through the fertility clinic they visited.
• It appears that each file that MDR is refining is related to a particular type of trauma: dental work, flying incidents, domestic violence or oppresion. My guess is that the last room/file that hasn’t been revealed yet (Cold Harbor) will be about the trauma of losing a loved one. This would also mean that Lumon scored a double win by faking Gemma’s death: they not only got her as a test subject for all these things, but they also got Mark, someone intimately familiar with the trauma of losing a loved one, to work on that file. That’s why they say that they need him specifically for that file.
• This last one implies that what MDR is doing is looking at neural patterns (the numbers on their screen) and removing/blocking specific sections that are affected by those traumas.
• To me, this solidified the idea that one of the main themes of this show is essentially that saying: “the road to hell is paved with good intentions”. Lumon essentially has “good intentions” of eliminating trauma from the world, but they are doing absolutely evil things in order to accomplish that. This also brings to mind the animal experiments (essentially torture) that are done for the purpose of developing life-saving or life-improving medicines.