Just a whiff of certain smells can instantly take me back to my childhood. When I smell fresh bread or apple cake right out of the oven, for example, I remember sitting around the dinner table with my parents and sisters for the holidays. Although odors can be a powerful memory cue, they are little understood cognitively.
In a new paper in the Journal of Cognitive Neuroscience, researchers explored what happens in the brain after exposure to certain smells. “We wanted to know if a very brief whiff, pleasant or unpleasant, could create a sustained brain state that bridges the gap between the smell and the next event, in our case, viewing a picture,” says Joan Tarrida Vidal of the University of Barcelona, lead author on the paper. “We were seeking to understand whether this odor-induced state could enhance or shape memories for something completely different that happens several seconds later.”
They found that brief odor cues have a lasting effect on both neural activity and memory performance. I spoke with Tarrida Vidal about these results, his early interests in odors, and the technical challenges studying smells can pose.
CNS: How did you become interested in this research area? Why study odor and cognition?
Tarrida Vidal: Everything began during my childhood. I have to admit that, since I was a child, odors have fascinated me. I remember going to a perfume store with my mother when I was about 10 years old and spending hours smelling pleasant fragrances on paper blotters and truly enjoying it.
When people asked me what I wanted to do when I grew up, I would always reply: “A scientist who discovers things!” Many years later, my PhD supervisors gave me the opportunity to explore a topic that had always fascinated me.
In addition, compared with other sensory modalities, I believe that olfactory cognition is understudied in humans. This might happen probably because of the technical challenges it poses.
CNS: What kinds of challenges do they pose?
Tarrida Vidal: Studying odors is very different from showing a picture on a screen or playing a sound through headphones. With odors, you’re actually sending molecules into someone’s nose, and that makes everything much more complicated. You need to acquire the right chemical compounds, dilute them carefully, and store them properly.
Timing is another big challenge. Odors don’t appear instantly the way a picture or a sound does, so experiments take longer, and it’s harder to control exactly when the odor reaches the participant. That precision is crucial if you want to combine odors with techniques like EEG or fMRI. To achieve this, we use olfactometers together with breathing and molecule sensors, which allow us to deliver the odor at just the right moment and to know the exact moment it reaches the participant’s nose.
And then there’s the cost. Commercial olfactometers are very expensive, so usually only labs that specialize in olfactory research can justify that kind of investment. In our case, we actually built our own device, inspired by a published design from Lundström and colleagues, which was a challenge in itself but also a rewarding part of setting up this line of research.
CNS: What general role does odor play in memory?
Tarrida Vidal: Before answering this question, I want to point out that when we talk about “memory,” we often put several different cognitive processes into the same category. However, when most people talk about memory, they usually mean autobiographical memory, which is just one form of memory.
In that context, odors play a special role by acting as cues that trigger memories. Larsson and colleagues proposed the LOVER model (Limbic, Old, Vivid, Emotional, and Rare), which describes how odors often cue memories that are emotionally significant, linked to childhood, recalled with great vividness, and that occur infrequently.
CNS: What were you most excited to find in your recent study?
Tarrida Vidal: The most interesting result was that odors affect our brains even when the chemical molecules are no longer present, showing that odors influence the brain in a slower and more persistent way.
Although our study focused on the encoding of information presented later in visual modality, and not on autobiographical memory, the behavioral results were still surprising. We cannot say that odors are universally good memory cues, but we did observe that, even without increasing overall accuracy, they play a role. In this case, unpleasant odors biased participants’ memories.
CNS: Were there any novel approaches in your study that you would like to highlight?
Tarrida Vidal: One highlight for me was using classifiers to see whether we could distinguish odors from non-odors based solely on neural activity. And this was indeed the case. However, we could not distinguish between pleasant and unpleasant odors from brain activity alone.
CNS: What do you most want people to understand about this work?
Tarrida Vidal: Even a quick whiff of an odor can leave a lasting trace in the brain, one that lingers for several seconds after the smell is gone and can subtly influence how we remember things that happen moments later. Our work shows that this lingering brain state is strong enough to tell odors from non-odors just by looking at neural activity, highlighting how smells can shape memory in ways we might not even notice.
CNS: What’s next for this line of work?
Tarrida Vidal: We want to continue exploring the impact that the hedonic component of odors has on human cognition. Our next research aims to investigate whether these hedonic aspects can be used as rewards or punishments in humans, and to understand whether pleasant or unpleasant odors can promote faster and more effective learning.
CNS: Is there anything else I didn’t ask you about that you’d like to add?
Tarrida Vidal: Yes. I would like to highlight that our research group had never worked on olfaction before. We built a lab specifically for this line of research and went through the entire learning process from scratch. Dealing with the technical challenges that odors present is one reason why the field is not even bigger. But our experience shows that it’s possible to build an olfactory lab with enough work, persistence, and passion for it.
-Lisa M.P. Munoz
