I read this short story when I was a teenager. I had thought it was Asimov, but can't find reference to it. I would like to know the author and name of story if anyone knows for my own teenage son. The story line as best as I can remember:
The story starts in the future where people are assigned roles based on accurate tests which are rarely wrong. A bank clerk who experiences worsening headaches one day has a mind explosion and he is instantly much higher intelligence and re-tests far above his prior job which is unheard of. I think this happens a couple of times and he becomes clairvoyant and somehow travels to the future where he learns that he was experimented on and a future criminal had put a stolen experimental 'Super-brain x' in his head. He meets the highly intelligent future humans but has become more intelligent than them and becomes telekinetic also and starts being able to control matter at an atomic level. He realizes that a catastrophic event stemming from a published journal in the past would destroy the world. He travels back to the past to stop a guy from publishing the incriminating paper. Due to a series of events he is forced to fuse his own body with that of the writer and throw their bodies into a furnace. In the future an examiner questions the validity of naming the original time traveler who gifted the brain as a criminal and surmises it was fortunate he acted as he did.