What is the test for causation in a First Amendment retaliation claim?

The causation element of a First Amendment retaliation claim requires the inmate plaintiff to show that protected conduct was the substantial or motivating factor underlying the defendant's adverse action. Brodheim v. Cry, 584 F.3d at 1271. "Recognizing that the ultimate fact of retaliation for the exercise of a constitutionally protected right rarely can be supported with direct evidence of intent that can be pleaded in a complaint, [citation omitted], courts have found sufficient complaints that allege a chronology of events from which retaliation may be inferred.