Abstract: An approach is provided for real time stimulus triggered by brain state and includes receiving data that indicates a brain state and a set of one or more stimuli associated with the brain state. Onset of an instance of the brain state is detected in a subject. In response to detecting onset of the instance, application to the subject of a stimulus of the set is initiated before the instance ends. In some embodiments, the brain state is determined based on a range of values for a function of brain signal data, wherein the range of values is associated with desired performance in response to an associated stimulus. The approach can enhance performance, enhance learning or enhance the probing of impact of that state on perception, action or cognition.