The Optics of Memory

By Paul Pietsch

Adapted from an article originally published in the December 1975 issue of Harper's Magazine (vol. 251, No. 1507).

In the spring of 1965, two physicists, Bela Julesz and K. S. Pennington, called attention to a similarity, in principle, between a then new type of optical hologram and memory stored in living brains. Neurophysiologist Karl Pribram soon published similar observations, but on experiments on the brains of lab animals.

Optical holograms (as opposed to microwave- electron- acoustical- and even computer-generated holograms) reconstruct vividly realistic images. It is often necessary to try touching the objects to verify their intangibility. But the hologram produces neither illusion nor hallucination. In the most rigorous sense, the image is identical to one the original scene produced when the hologram was made. The optical hologram is optical memory in its most total form.

HECK OF AN ENGINEER

The hologram Julesz and Pennington had in mind had just been discovered by a pair of engineers, Emmett Leith and Juris Upatnieks, and represented the beginning of holography as practiced today. The basic holographic principle -- capture of a complete code of a wave front -- had been discovered in 1947 by Dennis Gabor. But Leith and Upatnieks devised methods to make Gabor's code virtually sizeless and to endow every part of the exposed film with a complete record a scene's entire image. This equipotential property meant the whole message can be reconstructed from only a fraction of the hologram.

LAB BRAINS

Equipotentiality was precisely what psychologist Karl Lashley had spent a lifetime demonstrating about the brains of laboratory animals. The stored stuff of our minds has incredible capacity to survive massive injury to the brain. What Julesz and Pennington proposed, in other words, would resolve previously unexplainable facts about living brains, not with hat tricks, but with scientific principles.

Any equipotential brain theory would predict that stored facets of the mental world do not depend directly on the brain's anatomy, though it, doubtless, is essential in loading and calling upon information or in putting programs to specific uses, such as in vision or in language.

SHUFFLING THE DECK

I've been testing such ideas for several years by transplanting and reorganizing the brains of salamanders. My point of departure is to imagine memory as a deck of cards with all the suits and numbers on each card; shuffling the deck would not change the deal. In earlier experiments, I found that drastic shufflings of a carnivorous salamander's brain do not scramble the beast's appetite -- an instinctive behavior.

LOOKING UP

Since then, I've extended shufflebrain research to learned behavior. Let me summarize one series involving what I call the "looking-up" paradigm.

The adult axolotl, a Mexican salamander that spends its whole life in water, learns very quickly to look up when someone taps the side of its bowl and rewards it with a jiggling piece of beef liver or a live earthworm. Soon, tapping alone calls forth the response, even after weeks with immediate reward.

image

BRAIN TRANSPLANTS

My experiment was to transplant various parts of a trained adult's brain into the head of a naive larva. What happens is this: a previously naive host becomes a looker- up without any training. The transplant alone suffices to give the animal the necessary memory. Neither the part of the brain, nor the site in the host's cranium changed the results. What about the donors? They still remember the task. In other words, the necessary information existed both in the pieces of transplanted brain and in the parts left in place.

MEANINGS

The implication is that memory is hologramic;* all memory can theoretically be contained in the smallest unit of the medium, whatever that may be.

When I began shufflebrain research in earnest, my intentions were to refute the basis for any hologramic memory theory and substitute an alternative of my own. My theory has long since vanished. What Julesz and Pennington suggested a long time ago has survived every test thus far conducted in my laboratory. Where it will lead, we still really don't know.

*Larry Burns, my editor on this piece, suggested "hologramic" when I grumbled about "holographic;" the latter can mean a hand- written will (and who wants to associate wills with the search for minds!). In addition, I didn't want to induce embarrassment, chagrin or indigestion among honest- to- goodness holographers.
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pietsch@indiana.edu