A vivid and bizarre dream conjures up a myriad of novel mental images. The same exact images can be created volitionally when awake. The neurological mechanisms of these two processes are different. The voluntary combination of mental objects is mediated by the lateral prefrontal cortex and patients with damage to the LPFC often lose this ability. Conversely, the combination of mental objects into novel images during dreaming does not depend on the LPFC; LPFC is inactive during sleep and patients whose (...) LPFC is damaged do not notice a change in their dreams. Neither colloquial English nor scientific jargon has an established way to report on the origin of a conjured up mental image; the term “imagination” is regularly used to describe any experience generated internally whether voluntarily or involuntarily. Failing to distinguish be­tween voluntary and involuntary imagination leads to confusion in developmental psy­chology, neurolinguistics, and paleoanthropology. A comprehensive understanding of the distinction between voluntary and involuntary imagination will help develop better thera­py for children with language delay, contribute to a clearer understanding of the unique­ness of human language, and enable a more productive discussion of the evolutionary ori­gin of human language. (shrink)