Altered state of consciousness

An altered state of consciousness (ASC), or altered state of mind, is any condition which is significantly different from a normal waking state. The expression was used in 1966 by Arnold M. Ludwig, and brought into common usage by Charles Tart. It describes induced changes in one's mental state, almost always temporary. A synonymous phrase is "altered state of awareness".
Altered states of consciousness can be associated with artistic creativity, or different focus levels. They also can be shared between people and studied as a subject of sociological research.
States of consciousness.
During an altered state of consciousness, brain waves occupy different frequencies (i.e. Epsilon, Delta, Theta, Alpha, Beta, Gamma). These waves can be measured by electroencephalography (EEG). Also, subjective reports and observer reports of behaviour are used to identify the altered state.