A dream can be described as a succession of internal mental pictures or images, ideas, emotions, and sensations that typically occur involuntarily in the mind during specific stages of sleep, notably during rapid-eye movement (REM) stage of sleep. During REM, brain activity is high and resembles that of being awake. According to Wikipedia, the content and purpose of dreams are not fully understood, though they have been a topic of scientific speculation, as well as a subject of philosophical and religious interest, throughout recorded history. Dream interpretation is the attempt at drawing meaning from dreams and searching for an underlying message. The scientific study of dreams is called Oneirology.