A method of maintaining a state in a subject includes measuring one or more physiological parameters of the subject, calculating, using the measured parameter(s), a value, determining if the calculated value is below a lower threshold or above an upper threshold, and generating an output to the subject if the calculated value is determined to be below the lower threshold or above the upper threshold. In one embodiment, the generating an output to the subject includes generating a first output if the calculated value is determined to be below the lower threshold and generating a second output if the calculated value is determined to be above the upper threshold, the second output being different from the first output.