Science Making Gains in Memory Study
Much about the workings of memory remains mysterious. But scientists are learning more about its biology and operation.
“You can think of memory, or remembering, as a set of mental events very similar to perception,” said Fergus Craik, of the University of Toronto.
When we perceive something, our brains take in information from our senses and compare it with our storehouse of knowledge--our memories--in order to make sense out of the information and act on it.
When we try to remember something without input from our senses, he said, “we try to reconstruct from the inside some faint copy or simulation of the processes that went on at the time of the original perception.
“Sometimes it is very literal--a face, or the layout of a room. In other cases, it is not so much the surface aspects, but what we abstracted from the perception,” for example, whether it was good or bad, threatening or benign.
Scientists no longer believe that whole memories are tucked away like file folders in four or five cells at a discreet location in the brain. That idea originated in now-discredited experiments with patients who reported vivid childhood memories when surgeons touched points in their brains with tiny electrodes.
Modern imaging of brain cell electrical activity and blood flow, Craik said, shows that “it’s more accurate to think of memory as being widely distributed within the brain, probably with a tremendous amount of overlap . . . just as perception is a very widespread activation in the brain. There’s a network of neurons which, when activated, will give us the experience of remembering.”
Individual brain cells, or neurons, probably play a role in a variety of perceptions and memories, he said, much as the 26 letters of the alphabet can be combined with others to form hundreds of thousands of words. With billions of brain neurons to work with, “we’ve got, for all practical purposes, an infinite number of combinations of neurons.”
Just how we manage to activate a precise combination of neurons to dredge up a memory isn’t clear. Certain pathways are “hard-wired” at birth, but most seem to be established through the interworking of the senses and experience through the learning process.
“Once a particular network of neurons becomes associated with some meaning or experience, by whatever means the network is activated, it will again give rise to one experience and to some extent the meaning,” Craik said. “We build up our perceptual world from there.”
New experiences can “color,” alter or rearrange the old memory pathways, adjusting them to fit the new information. The neural connections are also vulnerable to damage and decay.
Brain surgery, alcohol, distractions, injury and strokes can wipe out parts of memories, or the capacity to process memories. And memory loss is a natural part of aging.
Pharmaceutical companies are engaged in a billion-dollar race to develop drugs that will enhance brain cell performance, Craik said. But “at present , there is nothing that everybody agrees really works.”
