We understand The Great Twitch as an extension of the Great Sleep. Like the Sleep, the Twitch is a coping mechanism that allows Jack to continue functioning in the world after he learns that Anne and Willie are having an affair.
This testifies to the depth of Jack's love for Anne, and probably for Willie too. The knowledge of their affair colors his world in a particularly ugly way. In fact this affair emphasizes all the other ugly aspects of life that Jack has already experienced. He has to "change the picture in his head" to survive. He has to dehumanize Anne and re-dehumanize Lois to deal with the movie of Anne and Willie that is playing in his brain. He says, "In the end you could not tell Anne Stanton from Lois Seager" (7.190).
The Twitch is his attempt to lobotomize himself like Adam's patient. If nothing has any meaning, if all life is electrical impulse, then feelings and pain are just an illusion. Jack dreams up the Twitch as a way to keep functioning in spite of his hurt and disillusionment.
The fact that he does keep functioning, that he does keep on seeking the truth even after the Twitch eventually allows him to renounce the Twitch at the end of the novel. He gives it up in favor of empathy and embracing the humans still left standing, including Anne and the Scholarly Attorney.
In the end, the Twitch is revealed as a temporary shield against the pain of a land soaked in the horrors of slavery. Jack's removal of this shield is like his peeling back layers of history to get to the truth. In both cases hope is only possible when the facts are all out in the open.