A method of maintaining a state in a subject (12) comprises generating a pacing signal (20) at a first frequency, presenting to the subject an output based upon the generated pacing signal, measuring one or more physiological parameters of the subject, detecting that the measured parameter(s) conform to a desired state in the subject, and either removing the presentation to the subject of the output based upon the generated pacing signal, or generating a new pacing signal at a second frequency, and presenting to the subject an output based upon the generated new pacing signal. The method can further comprise, prior to the detecting that the measured parameter(s) conform to a desired state in the subject, adjusting the pacing signal according to feedback from the measured parameter(s). In a preferred embodiment, the method also further comprises detecting that the measured parameter(s) no longer conform to a desired state in the subject, and presenting to the subject an output based upon the original generated pacing signal.
