Scents and Senses: The Phenomenon of Scent-Triggered Responses

smelling a roseThe holiday season is around the corner, which means family, friends, gifts, and food…lots of food. Not only do our taste buds bask in the delights of the season, but our noses are also filled with the sumptuous smells of feasts. The delicious scents of spices, baked pies, turkey, and gingerbread not only thrill our olfactory senses, but also trigger memories of bygone days. Theory suggests that with these memories, scents can change our mood and influence our behavior. Many of us have experienced the homey, comfortable feeling that glides over as when we smell cookies baking, or the relaxing feeling when we detect lavender or chamomile in our bath wash. Scent marketers and aroma therapists love the stuff—they have us wrapped around our fingers with this olfactory phenomenon, and they know it. How exactly does this happen? How can we get a whiff of something and suddenly be transported back to another moment?

The key is the limbic system, of which the olfactory bulb is part, and which is aptly nicknamed the “emotional brain”1 or, more specifically, the “feeling and the reacting brain”5. It controls functions on the autonomic and endocrine levels, most especially in response to emotional triggers. Many areas, some of which are connected to the olfactory system, are also essential in memory formation5. Once olfactory receptors connected to the limbic system are activated, the information is sent to the cortex, where the scent is recognized. This means that the emotional responses triggered by scents occur before the scent is even recognized2.

The olfactory bulb is like a factory for taking in and processing odors, then packaging the information up into little molecules called neurotransmitters and sending them on their merry way—to other important brain centers like the amygdala and the hippocampus. The amygdala processes sensory information by giving the info emotional importance, and it’s also the most crucial player in the fear conditioning and fear-memories4. Another brain center that receives this sensory information from odors is the hippocampus, which allows the brain to learn through association, forming connections between senses as experiences occur and are repeated. Through the pathways they travel down, odors can elicit responses to locations and events by stirring up memories that were formed long before, due to conditioned responses—the subconscious linking of a person or thing or experience to an odor or odors1.

The basis for these connections can be found evolutionarily and comparatively, as scent is a vital for survival amongst many species. For example, when rodents smell the urine of a carnivore, neural activity patterns show spikes in the areas of the brain pertaining to fear, like the amygdala. The scent also causes the rodents’ pulses to speed up and their levels of stress hormones to raise quickly3. For these little guys, vision isn’t always reliable in their hideouts (which are oftentimes dank and dark), so smell is the best way to go. But what about humans? In the hunting and gathering days, scent might have been used as a survival tactic, but how does it affect us in the modern day and age? Yes, odors can trigger memories, quite powerfully, in fact. But can our moods drastically change?

There are theories about the physiological mood shifts caused by odors. The difficult part of measuring how accurate this assertion is has to do with the difference between an actual neurophysiologic effect and the expected effect2. Say your ex-significant-other used to have a dog that was bathed far less than he should have been, and had that stench so particular to unwashed dog. Later down the road, you might encounter scruffy, smelly dog that reminds you of your ex’s Labrador, and, by association, your ex. It isn’t clear to scientists whether the connected neurons between your olfactory bulb (odors are received and processed), your amygdala (emotions are triggered), and your hippocampus (memories awaken) can actually summon feelings of sadness, or whether you simply think about the break-up and expect to feel sadness. That “calming” body wash, with the chamomile and the ylang-ylang and the lavender, might have a calming effect on you only because the bottle tells you so…but if that’s true, then how to we command our bodies to relax?

Psychologists and neuroscientists have studied olfactory memory for some time, and have made headway in various aspects of the phenomenon, but questions remain. For now, it’s comforting to know that hot apple pie can remind us of home and family, and mowed grass can bring back memories of sunny summer days.


  1. Dowdey, Sarah, “How Smell WorksHowStuffWorks.Accessed November 17, 2012.
  2. Fox, Kate. “The smell report.” Social Issues Research Center. Retrieved June (2007).
  3. Rosen, Meghan, “Scent Into Action.” ScienceNews, October 20, 2012. Accessed November 16, 2012.
  4. Sah, P., E. S. L. Faber, M. Lopez De Armentia, and J. Power. “The amygdaloid complex: anatomy and physiology.” Physiological reviews 83, no. 3 (2003): 803-834.
  5. Swenson, R. S. “Review of clinical and functional neuroscience.” Educational Review Manual in Neurology (2006).
  6. Image credit (Creative Commons): Twistiti, LL. “Smelling a rose, feeling loved, feeling alive.” Flickr. Taken June 12, 2008.

Tina Shah is a student at Cornell University. Follow The Triple Helix Online on Twitter and join us on Facebook.