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Decades ago American neuroscientist Karl Lashley went looking for the elusive engram: the trace of memory. Where precisely, he wanted to know, was the safe deposit box that held each memory in the brain? Was there a specific spot in the cortex that stored this precious data and kept it ready for retrieval at a moment’s notice?
To find out, he trained rats to complete a maze, drawing them to the end with a food reward. Then—science being science—he methodically snipped out discrete parts of the animals’ cortical tissue and, once healed, had them run the maze again. The aim was to see if, by process of elimination, he could discover which piece of a rat’s brain held the memory of the correct path. What he found was surprising: No matter which part he surgically removed (or destroyed by lesion), the rats still found the food. What mattered wasn’t where he cut, but rather how much. And indeed, the rodents could lose a substantial portion of their gray matter and still complete the maze, once it was learned.
Among his many conclusions: Memory isn’t held in any one storage locker of neurons; in a sense, it is both nowhere and everywhere, distributed across the brain in untold ways.
Lashley was right, it turns out, and a little wrong: We know from functional MRI studies, among other tests, that memory does have a regional component, too. But the idea that memory is a phenomenally complex collective function remains with us today.
Indeed, its complexity—and difficulty to pinpoint or characterize—speaks to how “alive” memory is. Our memories are what make us who we are. “The study of human memory is the closest one can get to a systematic study of the human soul,” writes Gabriel Radvansky, a professor at Notre Dame who has authored textbooks on memory. Caltech professor Ralph Adolphs frames it another way in a fascinating article entitled “The Unsolved Problems of Neuroscience”: “Memory may be the ability to predict the future by learning.”
This is where a big challenge for deep learning comes in, a topic on which my colleague Roger Parloff wrote about eloquently and insightfully in Fortune’s October 1 issue. Ultimately, deep learning will enable us to solve riddles of biology and well-being that may now seem just out of reach—including the sad problem of failing memory as we age.
Today, though, let us use the power of our memories to remember those who have served and fallen in the name of country and duty. Honor Veteran’s Day.
