ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Sunday, July 21, 1996 TAG: 9607190088
SECTION: EXTRA PAGE: 5 EDITION: METRO
SOURCE: MATT CRENSON ASSOCIATED PRESS
At the beginning of Marcel Proust's ``Swann's Way,'' we find the author kicking back in his mom's kitchen on a cold day.
He savors the flavor of a madeleine chunk floating in a spoonful of hot tea. The aroma of the tea-soaked cake wafts into the warm, cozy room.
More than a million words later, the effects of that scent have finally worn off. Proust has semiautobiographically recounted his entire life in seven volumes of vividly descriptive prose, all brought to his conscious mind by the smell of a soggy cookie.
Psychologists call that experience the Proust phenomenon, and their most recent investigations show that it's real. Memories dredged up by flavors and odors feel more vivid and emotional than those brought on by sights, sounds and tastes; in the case of flavor, taste is actually less important than smell.
Recent research shows that the brain handles information from the nose in a unique way, sending it directly to the parts of the brain associated with memory and emotion. In contrast, sights, sounds and sensations are routed through the brain's analytical apparatus before reaching more primitive, emotional areas.
That explanation fits with the evolutionary picture, because smell is the most primitive of the senses. Long before animals were spotting lions in the bushes, or flying off at the sound of a snapping branch, they were sniffing at the world around them in an effort to figure out what they should move toward and what they should avoid.
That was in the days before the cerebral cortex, the part of the brain that allows higher animals to perform impressive cognitive feats. Vision, hearing, touch and taste all connect to the cerebral cortex before linking to the brain's more primitive parts. But smell heads straight for the limbic system, an area so primitive it's sometimes known as the ``reptile brain.''
The limbic system includes the hippocampus, a brain area closely associated with memory. It also contains the amygdala, which neuroscientists have recently identified as a center for emotions. Researchers think the close interaction of the olfactory system to those two areas may explain the results of some recent experiments that demonstrate the Proust phenomenon.
Rachel Herz of the Monell Chemical Senses Center in Philadelphia has done a series of studies showing that, of the five senses, smell is unmatched in provoking emotional memories.
In one experiment, she had subjects look at paintings and associate them with either an odor or a word for that odor. For example, a subject might look at Renoir's ``Luncheon at the Boating Party'' while either actually smelling lemon or being told to imagine that smell.
The subjects looked at 16 paintings in all - eight while smelling an odor and eight others while just thinking of the odor. Then they went home.
Two days later, the subjects came back to the lab. Herz and her colleagues presented each subject with the odors they had smelled, and also with the words they had thought of. With each odor or word, they asked the subjects to identify the painting that went with that cue and write a brief description of it.
That experiment, and others like it, have brought Herz and her colleagues to a surprising and revealing conclusion. Smells didn't help people remember the paintings they saw any better than words did - they could recall paintings paired with words about as reliably as they could paintings paired with odors.
But when it came to the descriptions the subjects wrote, there was a big difference. When subjects connected the painting to the word ``lemon'' for example, they wrote a simple factual description of the painting. But when they smelled a lemon and then described the painting that went with that scent, their descriptions contained much more information about the painting's emotional content.
``Our experience of emotion might be very different if we did not have the sense of smell,'' Herz and Trygg Engen of Brown University in Providence, R.I., write in a paper that has been accepted for publication in Psychonomic Bulletin & Review.
Larry Cahill, a neuroscientist at the University of California, Irvine, has found patterns of brain activity that support that contention. Those patterns also provide physiological evidence for the close connection of smell and memory.
``There's a lot of interconnections going on here at this point,'' Cahill said.
He and several colleagues have found that the amygdala plays a key role in recording emotionally charged memories. Meanwhile, brain imaging studies performed at the University of Minnesota in Minneapolis are finding that the amygdala becomes much more active in response to unpleasant odors.
``Add the fact that this little structure the amygdala gets input from the nose, and you have food for thought,'' Cahill said. ``It's a very interesting possibility that strong emotions created by odors might affect memory through the amygdala.''
In a recent letter to the British journal Nature, Cahill and James McGaugh of the University of California, Irvine, and Ralf Babinsky and Hans Markowitsch of the University of Bielefeld in Germany described the plight of ``B.P.,'' a man suffering from a rare disease that causes brain damage in the amygdala.
Despite his brain damage, B.P. was normal in most ways. But he differed from normal subjects in one small area - he couldn't remember emotionally charged events any better than dull, everyday ones.
In experiments where people without damaged amygdalas saw a slide show that graphically depicted the injury of a young boy and its aftermath, they reacted in horror. One week later, they also remembered that slide show better than one about the same boy's uneventful visit to the hospital.
When B.P. saw the slide show depicting the young boy's injury, he reacted just as intensely as did people with intact amygdalas. But later, he didn't remember the gruesome slide show any better than the less emotional one. For some reason, the damage to B.P.'s amygdala prevented him from translating that intensity into a more durable memory.
``The data suggest that the amygdala was really critical for translating the emotional reaction into heightened recall,'' Cahill said.
That helps explain why memories brought on by smells feel so strong. But to find out why smells are so tightly wired to specific memories - such as the awful thing that happened in the locker room that day during junior high - neuroscientists have to look at another primitive brain area.
That area, the hippocampus, is important to retrieving memories associated with experience. It's also closely connected with the amygdala.
In an experiment with rats with brain damage in the hippocampus, Howard Eichenbaum and Mike Bunsey of the State University of New York at Stony Brook found a sophisticated smell-associated memory system.
The rats were trained to follow a series of scents to a food reward. Both the scents and the rewards were held in little cups filled with sand and rat chow.
In the simplest task, the rats learned that if the first cup they smelled contained cocoa, for example, they could find a treat hidden in a coffee-scented cup. Even the brain-damaged rats could master that exercise. But when the scent cues were reversed, they foundered. Smelling coffee didn't send them to the cocoa-scented cup. The rats with intact hippocampi, however, had no problem figuring out that if cocoa goes with coffee, the reverse might also be true.
The rats with damaged hippocampi also failed in a more complicated task, where they were required to associate three smells. In that case, they were trained to connect smell B to smell A, and smell C to smell B. Then they were presented with smell A, which led the normal rats to smell B, and then to the food reward in the cup containing smell C.
``We asked animals to make inferences about memories they had obtained,'' Eichenbaum said. ``What that kind of organization of memory provides you with is a way to really use your memories instead of just making a habitual response.''
Because the rats with damaged hippocampi failed to make those inferences, Eichenbaum and Bunsey concluded that the hippocampus confers rats with flexible access to their memories. They're not just performing conditioned responses to smells, but using their memories in a creative way.
Eichenbaum compares it to the way that people recognize faces, which often evoke something similar to the Proust phenomenon. For example, many people see Richard Nixon's face and vividly recall certain emotionally charged political events.
Obviously, the way people remember those events depends on how they experienced them at the time. And smells are the same way, researchers have found.
For example, when University of Minnesota researchers were trying to evoke emotional responses to smells for their brain imaging studies, they found some unusual preferences. In one case, a subject expressed intense pleasure at the smell of intestinal gas.
``She had spent a wonderful summer in Alaska,'' Minnesota psychologist Jose Pardo explained. ``She'd spent the summer at a gas refinery.''
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