Originally published 8 April 1991
It’s a familiar story, but I’ll tell it again.
Marcel Proust, 42 years-old, takes a bite of cake, a madeleine. Instantly, the taste evokes memories of his childhood, of Sunday mornings at Combray, of visits to his aunt Leonie in her room, of the pieces of madeleine that she gave to him, dipping them first into her lime-blossom tea. That trickle of memories becomes the flood which is the novelist’s great work, Remembrance of Things Past.
How do memories happen? Some years ago the fashionable view held that memories are stored in the brain as molecules, proteins, or RNA molecules that have somehow been modified by experience. Most recent research, however, supports the idea that memories are stored as networks of interacting nerve cells, or neurons.
According to the current view, experience tunes the connections, or synapses, between nerve cells, creating a different “trace” of interconnected cells for each memory. Remembrance, then, must be imagined as a cobwebby thing, an invisible net of electro-chemical connections infiltrating the brain, triggered into consciousness for Proust by the taste of a tea-dipped cake.
Forgotten memories
Someone asked me the other day about my first automobile accident. A fender-bender in 1962 came immediately to mind. But that was not the first. The first was forgotten, buried deep among the souvenirs of youth collected and forgotten in the attic of the mind.
Then, a few days later, I heard a song on a local “oldies” station, the Weavers singing “Goodnight Irene.” Bingo! There went the car, my Dad’s pale green 1950 Ford, careening off the road, through a hedge and into a ditch, voices from a portable radio in the backseat crooning “I’ll see you in my dreams.”
Instantly came the flood of remembered details: The girl by my side, the cause of the loss of control at the wheel. Her short-cropped hair, with a dizzy peroxide streak. Her fuzzy angora cardigan. The dainty gold watch loose on her wrist, a 9th grade graduation present. Penny loafers sloughed off. Painted toenails.
Where does all this stuff come from, this American Graffiti scene from the past? How was it stored in the brain, waiting to be made instantly real. As fine-tuned synapses? Then how are the synapses tuned? What sort of chemical magic happens at the junctions between nerve cells to make these memories permanent in the brain? Neurologists have given the process a name — long-term potentiation, or LTP for short — but they are pretty vague about what exactly happens.
The signal that passes from one neuron to another is carried by molecules called neurotransmitters. Is the connection between neurons strengthened by the release of extra neurotransmitters by the transmitting neuron? Or does the receiving neuron merely become more sensitive? How is all this chemical activity triggered by experience? And how do those zillions of cobwebby synaptic networks stay active and distinct for a lifetime?
An army of brain researchers is searching for answers, but progress is slow. There are as many as 100 billion nerve cells in the human brain, each cell in communication through a tree-like array of synapses with thousands of other cells. The possibilities of interconnection are staggeringly intricate, and, in principle, sufficient to record far more volumes of memories than even Proust managed to retrieve in his novel of more than a million words.
Somewhere among the cobwebby traces of my own brain are recorded: The Skyview Drive-In Theater, Robert Taylor and Elizabeth Taylor in Ivanhoe. Nervous kisses with a taste of Clorets. Her house after the movie. Dancing in the backyard under the pines and drinking Dr. Peppers. Rosemary Clooney singing “Come On‑a My House” on a new 45 RPM single. I spill Dr. Pepper on my plaid shirt. I’m glad it’s plaid so the spill won’t show. And then — the fateful spin in the car.
Networks of neurons
One hundred billion interconnected cells somehow remembering things that happened 38 years ago. The problem of figuring this out scientifically is next to impossible. No wonder memory researchers often choose to work with simpler organisms, the sea snail Aplysia, for example. The sea snail’s nervous system consists of only about 18,000 cells, many of them big enough to see with the naked eye. The snails can be trained to exhibit certain behaviors in response to stimuli, and chemical and electrical changes in their nervous systems can be monitored with relative ease.
But there are vast differences between Aplysia’s scanty net of neurons and the human brain. Can the sound of the Weavers singing “Goodnight Irene” evoke an ensemble of memories in a sea snail’s brain? Can a creature with only 18,000 nerve cells be said to properly remember at all?
It was a long time ago, that first automobile accident. The Bomb. Korea. Flying saucers. Stevenson vs. Eisenhower. Tony Curtis and Janet Leigh. And the girl in the angora sweater, distractingly pretty. A crunch of hedge, a jolting bump. The radio in the back seat bouncing off the roof of the car, the Weavers serenading though it all. Nothing hurt, except my pride. And some awkward scratches on the sides of my father’s car.
Red toenails and Cloret kisses, Rosemary Clooney and Dr. Peppers — details from the past, somewhat less than Proustian and perhaps best left forgotten, but indelibly etched in synaptic connections and resurrected by a song. Remembrances of things past: a monumental problem for science to solve and the inexhaustible stock-in-trade of novelists.
