Automatism re-visited: post-traumatic automatism as a defence to a serious criminal charge.

A case is described of a policeman who assaulted the man he was arresting after receiving a concussive blow to the head. The defence argued he was suffering from post-traumatic automatism and after juries were unable to agree a verdict in two trials he was acquitted. Aspects of post-traumatic automatism in English law are described and theories of the neurology of concussion and aggressive behaviour are discussed. Guidelines are proposed for the evaluation of cases of post-traumatic automatism.