From Oliver Sacks recent NY Times blog post on visual patterns seen during migraines...
"In my own migraine auras, I would sometimes see — vividly with closed eyes, more faintly and transparently if I kept my eyes open — tiny branching lines, like twigs, or geometrical structures covering the entire visual field: lattices, checkerboards, cobwebs, and honeycombs. Sometimes there were more elaborate patterns, like Turkish carpets or complex mosaics; sometimes I saw scrolls and spirals, swirls and eddies; sometimes three-dimensional shapes like tiny pine cones or sea urchins."
"We can actually see, through such hallucinations, something of the dynamics of a large population of living nerve cells and, in particular, the role of what mathematicians term deterministic chaos in allowing complex patterns of activity to emerge throughout the visual cortex. This activity operates at a basic cellular level, far beneath the level of personal experience. They are archetypes, in a way, universals of human experience."
"...Much later still, when I first saw photographs of the Alhambra, with its intricate geometric mosaics, I started to wonder whether what I had taken to be a personal experience and resonance might in fact be part of a larger whole, whether certain basic forms of geometric art, going back for tens of thousands of years, might also reflect the external expression of universal experiences. Migraine-like patterns, so to speak, are seen not only in Islamic art, but in classical and medieval motifs, in Zapotec architecture, in the bark paintings of Aboriginal artists in Australia, in Acoma pottery, in Swazi basketry — in virtually every culture. There seems to have been, throughout human history, a need to externalize, to make art from, these internal experiences, from the decorative motifs of prehistoric cave paintings to the psychedelic art of the 1960s. Do the arabesques in our own minds, built into our own brain organization, provide us with our first intimations of geometry, of formal beauty?"