The biological foundation of the mind's eye is not fully understood. Studies using fMRI have shown that the lateral geniculate nucleus and the V1 area of the visual cortex are activated during mental imagery tasks. Ratey writes:
The visual pathway is not a one-way street. Higher areas of the brain can also send visual input back to neurons in lower areas of the visual cortex. [...] As humans, we have the ability to see with the mind's eye – to have a perceptual experience in the absence of visual input. For example, PET scans have shown that when subjects, seated in a room, imagine they are at their front door starting to walk either to the left or right, activation begins in the visual association cortex, the parietal cortex, and the prefrontal cortex - all higher cognitive processing centers of the brain.
The rudiments of a biological basis for the mind's eye is found in the deeper portions of the brain below the neocortex, or where the center of perception exists. The thalamus has been found to be discrete to other components in that it processes all forms of perceptional data relayed from both lower and higher components of the brain. Damage to this component can produce permanent perceptual damage, however when damage is inflicted upon the cerebral cortex, the brain adapts to neuroplasticity to amend any occlusions for perception. It can be thought that the neocortex is a sophisticated memory storage warehouse in which data received as an input from sensory systems are compartmentalized via the cerebral cortex. This would essentially allow for shapes to be identified, although given the lack of filtering input produced internally, one may as a consequence, hallucinate - essentially seeing something that isn't received as an input externally but rather internal (i.e. an error in the filtering of segmented sensory data from the cerebral cortex may result in one seeing, feeling, hearing or experiencing something that is inconsistent with reality).
Not all people have the same internal perceptual ability. For many, when the eyes are closed, the perception of darkness prevails. However, some people are able to perceive colorful, dynamic imagery. The use of hallucinogenic drugs increases the subject's ability to consciously access visual (and auditory, and other sense) percepts. The Mental Imagery article goes into more detail.
Furthermore, the pineal gland is a hypothetical candidate for producing a mind's eye; Rick Strassman and others have postulated that during near-death experiences (NDE's) and dreaming, the gland might secrete a hallucinogenic chemical N,N-Dimethyltryptamine (DMT) to produce internal visuals when external sensory data is occluded. However, this hypothesis has yet to be fully supported with neurochemical evidence and plausible mechanism for DMT production.
The use of the phrase mind's eye does not imply that there is a single or unitary place in the mind or brain where visual consciousness occurs. Philosophers such as Daniel Dennett have critiqued this view. However, others, such as Johnjoe McFadden of the University of Surrey in the United Kingdom and the New Zealand-based neurobiologist Susan Pockett, propose that the brain's electromagnetic field is consciousness itself, thus causing the perception of a unitary location.
- Imagery of famous faces: effects of memory and attention revealed by fMRI, A. Ishai, J. V. Haxby and L. G. Ungerleider, NeuroImage 17 (2002), pp. 1729-1741.
- A User's Guide to the Brain, John J. Ratey, ISBN 0-375-70107-9, at p. 107.
- Rick Strassman, DMT: The Spirit Molecule: A Doctor's Revolutionary Research into the Biology of Near-Death and Mystical Experiences, 320 pages, Park Street Press, 2001, ISBN 0-89281-927-8
- Consciousness Explained, Daniel C. Dennett, Boston: Little, Brown and Company, 1991. ISBN 0-316-18065-3.
- Our Conscious Mind Could Be An Electromagnetic Field, UniSci.
- Synchronous Firing and Its Influence on the Brain's Electromagnetic Field: Evidence for an Electromagnetic Field Theory of Consciousness, J. McFadden, Journal of Consciousness Studies 9 (2002), part 4, pp. 23–50.
Prince Hamlet says, he sees his dead father "In my mind's eye, Horatio" (Shakespeare, Hamlet, 1.2.191, 193, Folger's Edition).