altered states of consciousness are altered states of certain brain systems. [...] The result is a dissociation between self-aware executive consciousness and its usual sources of sensations, memories, and emotions. When these neural systems are affected by disease, repetitive stimulation, mental manipulations, or chemical ingestion, our perception of ourselves and the world can be profoundly altered. For the duration, reality seems fundamentally changed. Although these dramatic interludes have often been taken to be supernatural, it is more likely that, in the words of the psychiatrist William Sargant, it is "... the brain of man and not his soul which is affected by mystical techniques.