A look at the map of the brain exposes all the secrets behind the intense connection between scent and memory. When a scent is first picked up by the neurons in the nose, an impulse is created and passed along to the olfactory bulb, the part of the brain that is responsible for analyzing smells. The olfactory bulb is part of the brain’s limbic system, an area of the brain that is also home to the amygdala and the hippocampus. The amygdala and the hippocampus play major roles in creating and controlling our memories, moods, behaviors, and emotions, lending the nickname the "emotional brain” to the limbic system. The close proximity between these sections of the limbic system explain why smells can bring up powerful memories almost instantaneously.
These direct connections make olfaction completely unique to our other senses. If we observe the major pathways our other senses travel, such as vision and hearing, we see a more complex route to the "emotional brain.” When our eyes and ears pick up senses, that information is initially sent to a part of the brain called the thalamus before moving on the rest of the brain. Meanwhile, the scent receptors in the nose are one quick synapse away from emotion and memory.
While, of course, memories can be triggered by a number of factors, odor-evoked recollections tend to be autobiographical memories and differ from those brought out by our other senses. In particular, autobiographical memories brought on by smells are typically older, more emotional, specific, vivid, and are relatively rare. Often happening spontaneously, as one usually encounters scents, these memories tend to be more unintentional. While it is totally typical for one to, say, listen to a song or look at a picture to bring up past memories, it is not exactly likely that one will go out and cut their grass to bring back a memory.
The fact that olfactory information doesn't first filter through the part of the brain that connects language to sensations, like our other primary senses do, also hints at why scent memory is more emotional. Our other senses’ more refined cognitive processes equate to being much better at coming up with words for sights and sounds than for odors. Meanwhile, describing things in words may, in many cases, aid memory but it also desensitizes us the emotional aspects of what we are trying to conjure up. When we create verbal narratives of our memories, our brains begin to remember the story just as much as the raw experience, making these experiences more intellectual than emotional.
Childhood memories are very often brought up by scents, this is because it is during our youth that we are first introduced to most odors. However, we actually start making connections between scent and emotions before we even grace the Earth. Our mother’s preferences are shared with us through amniotic fluid. Studies show that those exposed to alcohol, cigarette smoke, or garlic in the womb show a preference to these smells once they are born. These scents that are typically unsettling for babies, are neutral or even comforting to those exposed pre-birth.
The strong connection between smell and memory means there is much to lose in the case that our sense of scent is lost. The loss of olfactory function results in the loss of important sentimental pathways to memory and the repercussions may be way more serious than one would think. A dulled sense of scent is often apparent in people who have cognitive impairments, such as schizophrenia, Down syndrome, Alzheimer’s disease, and Parkinson’s disease. The diminishing of the ability to smell can even be early indicators of onset of the latter two, occurring years before motor skill difficulties occur.