Brain-computer interfaces allow agents to control computers without moving their bodies. The agents imagine certain things and the brain-computer interfaces read the concomitant neural activity and operate the computer accordingly. But the use of brain-computer interfaces is problematic for criminal law, which requires that someone can only be found criminally responsible if they have satisfied the actus reus requirement: that the agent has performed some (suitably specified) conduct. Agents who affect the world using brain-computer interfaces do not obviously perform any (...) conduct, so when they commit crimes using brain-computer interfaces it is unclear how they have satisfied actus reus. Drawing on a forthcoming paper by Allan McCay, I suggest three potential accounts of the conduct that satisfies actus reus: the agent’s neural firings, his mental states, and the electronic activity in his brain-computer interface. I then present two accounts which determine how actus reus may be satisfied – one a counterfactual and the other a minimal sufficiency account. These accounts are lent plausibility because they are analogous to the but-for and NESS (Necessary Element in a Sufficient Set) tests for causation which are generally accepted tests for causation in legal theory. I argue that due to the determinations of these accounts and considerations regarding the relationship between the mind and brain, actus reus is satisfied by either the agent’s neural activity or brain-computer interface electrical activity. Which of these satisfies actus reus is determined by how well the brain-computer interface is functionally integrated with the agent. (shrink)