The neophyte circuit, referred to by the Twelfth Doctor as a memory giver, was a piece of technology capable of rebooting any computer system and replacing any lost data. The Doctor noted that he had only ever seen one before in his life.
A neophyte circuit was kept in the Bank of Karabraxos. Being able to restore his memory, Psi, an augmented human, was promised the neophyte circuit as a reward for participating in the Doctor's plan to rob the Bank of Karabraxos. It was given to Psi by the Doctor, who discovered it with Clara Oswald in vault "TECH 251" (TV: Time Heist)