1. A method for determining respiratory cycle-related EEG changes (RCREC) for a subject, the method comprising: receiving an EEG signal from the subject using at least one EEG sensor; defining at least two respiratory cycle segments within each respiratory cycle; determining an EEG power of the EEG signal during each of the at least two respiratory cycle segments; and determining RCREC by calculating a difference between a maximum EEG segment power and a minimum EEG segment power.