The term neural block described various mechanisms used by different cultures.
Used by the Time Lords
The Twelfth Doctor tried to use a human-compatible neural block on Clara Oswald, given to him by a technician, to wipe Clara's memory of him, but Clara reversed the polarity using the sonic sunglasses and instead, the Doctor forgot most of his memories of Clara. (TV: Hell Bent) They were eventually restored by a glass avatar of Clara from the Testimony. (TV: Twice Upon a Time)
Used by Kovarian
The neural blocks used by Madame Kovarian, placed in Melody Pond from birth, were a precautionary measure to prevent her from killing Kovarian. Neural blocks were also placed in the proto-Time Lords created from Melody's DNA. Even when given reason to kill their former leader, River Song and her clones were unable to follow through and intentionally harm Kovarian, due to the neural blocks implanted in them.
River suspected that, given time, she might find a way to overcome them, as she had done her brainwashing with regards to the Doctor. The neural blocks did not prevent the proto-Time Lords from allowing Kovarian's death through inaction. (AUDIO: The Furies)