A method modifying a particular electrophysiological feature generated in response to a stimulus is disclosed. The method involves a repeated process of: sampling the brain wave state in order to apply a modifying pulse; modifying the brain wave state to a state more conducive to a required response; sampling the brain wave state in order to apply a response stimulus; applying a stimulus only when the brain wave state substantially meets the preselected response criteria; recording the brain wave activity of the subject subsequent to the application of the stimulus.