Warning: spoilers ahead for Episode 14 of The Flash Season 4, called "Subject 9."
The Flash has pitted Team Flash against what may be their most formidable foe to date with Clifford DeVoe, a.k.a. the Thinker. Unfortunately, Team Flash hasn't had much success so far, and their biggest victories to date may simply be recruiting Ralph Dibny and springing Barry from prison, and it's entirely possible that Barry's release from jail will be temporary. The good news is that the good guys finally seem to be making some headway against the Thinker, as "Subject 9" saw them developing the long-awaited cerebral inhibitor.
Well, technically Wells developed the cerebral inhibitor, and it didn't actually work as intended in "Subject 9." He got the idea after trying to help Cecile tune out all the thoughts she was accidentally picking up due to her pregnancy powers. If he could help her suppress her powers with technology, he could theoretically suppress the Thinker's ability to transfer his consciousness between bodies. The device was designed to work as soon as it could be affixed to the Thinker's forehead, and it seemed to be working for a bit when he (still in Becky's body) was attempting to transfer his consciousness into the body of another bus meta, Izzy.
Only a few moments passed before it became apparent that the device wasn't working as intended, despite the comment from Savitar back in Season 3 that Team Flash would use a cerebral inhibitor to battle a villain named DeVoe. The failure of the cerebral inhibitor meant that the Thinker was perfectly capable of absorbing another meta's powers and inhabiting her body. Before Becky's body could fail, DeVoe moved into Izzy's body, killing her in front of Barry and Ralph.
Obviously this first attempt at developing a cerebral inhibitor failed, and Izzy died for it. The odds are good that it was only the first of several attempts to create such a device, as the theory behind its design was clearly sound. The inhibitor may simply take some tinkering to stand up against the Thinker's assortment of powers. Perhaps Wells and the rest of the Team Flash brain trust will be inspired by Izzy's musical meta abilities. Oddly enough, her musical powers were the first meta abilities that seemed to do damage to the Thinker. If Team Flash can combine their collective intellect, the theory behind cerebral inhibitor 1.0, and what was so effective about Izzy's powers, perhaps they're on the road to defeating the Thinker.
Wells' invention of the cerebral inhibitor -- even though it failed -- is at least a sign that Team Flash might get moving on trying to take the Thinker down by using all of their resources. Given how long they've known that a cerebral inhibitor would play a part in the fight against the big bad, it was getting ridiculous that they weren't constantly tinkering with various tech to try and create a device. Hopefully "Subject 9" is a sign that Team Flash will finally put their heads together, use all their resources, and come up with a plan. At least they did manage to figure out that the Thinker's lair is tucked away in a pocket dimension in this episode. Knowing about the pocket dimension should come in very handy when it comes to using the cerebral inhibitor.