Olfaction and Memory

Have you ever had the experience where you perceive a smell and suddenly remember an event that you'd forgotten for years? Or, consider certain perfume or cologne smells that remind you of people in your life. These are examples of the connection between olfaction and memory. This section of our Web page will describe odor memory, which refers to both memory for odors and memories that are evoked by odors.

It is first important to understand the physiology of olfaction. The primary olfactory cortex, in which higher-level processing of olfactory information takes place, forms a direct link with the amygdala and the hippocampus. Only two synapses separate the olfactory nerve from the amygdala, which is involved in experiencing emotion and also in emotional memory (Herz & Engen, 1996). In addition, only three synapses separate the olfactory nerve from the hippocampus, which is implicated in memory, especially working memory and short-term memory. Olfaction is the sensory modality that is physically closest to the limbic system, of which the hippocampus and amygdala are a part, and which is responsible for emotions and memory. Indeed this may be why odor-evoked memories are unusually emotionally potent (1996).

It may be significant that olfactory neurons are unmyelinated, making olfaction the slowest of all the senses. It not only takes the brain longer to perceive olfactory stimuli; the sensation of an odor also persists for greater lengths of time than do sensations of vision or audition (1996). The fact that olfactory receptors are the only sensory receptors directly exposed to the environment may also help explain the relationship between olfaction and memory. Could it be that olfactory receptors most readily receive information from the physical world and therefore are readily able to code memories for things like emotion or events?

What is the nature of olfactory memory? Is it similar to memory for visual or auditory information? Certainly more research has been conducted in areas of visual and auditory information; many traits of odor memory have yet to be defined. For example, storage and decay processes, characteristics of memory processes, are not yet understood with respect to olfaction (1996). Neurological imaging techniques could further refine our understanding of the way odor memory works.

Although Engen and colleagues (Engen, 1987) claimed that odor memory does not have a short-term component, more recent research has supported the existence of olfactory short-term memory (White & Treisman, 1997). Although there is no evidence for olfactory primacy (the phenomenon in which stimuli presented at the beginning of a trial is remembered best), White and Treisman's experiment does provide significant evidence for recency in olfaction (1997). The researchers explained this finding by mentioning that primacy is accounted for by rehearsal, "a cognitive process that may not be available for odours" (1997).

White and Treisman posited that olfactory memory occurs because individuals assign verbal meanings to olfactory stimuli. They also claim that just as olfactory sense is a crucial sense for other animals, "there is no a priori reason why humans alone should lack an olfactory memory" (1997).

What kinds of olfactory stimuli are best remembered? Rabin & Cain (1984) found that odor memory was improved by familiarity and identifiability." Olfaction has often been implicated in learning processes, specifically in research done with animals. For example, in a study by Frances Darling and Burton Slotnick (1994))\, rats quickly learned to avoid licking at a drinking tube containing an odorant and quinine hydrochloride. Learning occurred relatively quickly: within only one or two exposures to this particular combination of odor and tastant. This study suggests, then, that the brain may be equipped with a mechanism for olfactory memory. Slotnick (1993) provides further evidence for olfactory learning in rats. He shows that rats have actually achieved errorless performance in olfactory learning tasks. W. Thomas Tomlinson (1991) showed that normally reared hamsters (versus hamsters reared on a liquid diet) demonstrated spatial memory for the location of odor cues in an allocentric (versus egocentric) task.

The fact that animals often employ the olfactory sense to locate stored food provides further support for the existence of an olfactory memory of sorts. Stephen B. Vander Wall (1991) showed that yellow pine chipmunks found caches (stored food) using their olfactory sense. However, in the study, olfaction only helped chipmunks localize moist seeds and not dry seeds. Olfaction therefore plays a part in an integrated system for recovering caches and finding hidden food.

Another way in which animals use olfaction is identifying their young. Gary F. McCracken did a study of Mexican free-tailed bats which examined nursing behavior of mother-pup pairs. He found that mother bats returned to areas where they had nursed previously, and hypothesized that olfactory cues were used to remember these places.

Research has also been done on odor memory in humans. It has been shown that patients of Korsakoff's syndrome, who suffer severe memory impairment, show less of an impairment for odor memory than for other kinds of memory. This suggests that there is in fact a mechanism for odor memory separate from other kinds of memory.

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