You'll find yourself back in Sasha's lab now and you are able to get back into the Brain Tumbler Experiment. However, if you've reached rank 20 by now you'll probably want to take a moment to go see Cruller for another Psi ability and stop in the lodge to buy the Cobweb duster so you hopefully don't have to backtrack through any of the future levels for cobwebs.
Off to Cruller's!