How do we “see” with our eyes closed when we are dreaming?
—Robert J. Evans, via e-mail
Robert O. Duncan, a behavioral scientist at York College, the City University of New York, explains:
as you suggested by the phrasing of your question, people don’t actually see in their dreams. Sight depends on light entering the eye and stimulating the retina—something that doesn’t happen when we are lying in the dark with our eyes shut. Nevertheless, studies that compare the vivid imagery of dreams with daytime vision reveal similar patterns of activity in the visual cortex, the largest brain area devoted to vision.
That is why some researchers believe dream visions come from visual centers in the brain. In the mid-1970s dream researcher J. Allan Hobson and his colleagues at Harvard Medical School proposed that the brain spontaneously generates electrical pulses while dreaming. These signals, known as PGO waves, originate in the visual cortex and in two other visual regions of the brain: the pons and the lateral geniculate nucleus.
PGO waves are most prominent during rapid eye movement (REM) sleep, the part of sleep when most dreaming occurs. The spontaneous activity from PGO waves may start in the visual areas of the brain but ultimately creates a cascade of activity that taps into the brain regions that house memories.
But not all investigators agree that dream imagery originates in visual areas. Several dream researchers have proposed the opposite path, suggesting that dreams originate in the regions that store memories and then connect to visual brain areas. This theory would explain why dream images are only as detailed as our memories.
For instance, let’s say you are thinking of your grandmother. Your memory of her might not include the mole she has on the right side of her face, something you would clearly see if you were sitting next to her. The lack of detail that is characteristic of memory occurs also in dream visions.