Not to be sniffed at: Aromas and memory

Memory is very closely linked to smell. We’ve all experienced that feeling where you catch a whiff of something and it instantly transports you back to an occasion from long ago. So why is this, and why are smells so memorable? Chris Smith spoke to Andy Johnson from the University of Bournemouth, who looks into this...

Andy - This is a very common phenomenon that our participants will often report and one possible explanation is related to the structure of the brain. The limbic system contains the system within the brain that deals with smell, but it also within that system is the memory and the emotion systems. So, because of their close proximity, it is possible that this leads to these very strong associations between particularly emotional memories and smells.

Chris - So a smell elicits activity in a very similar bit of the brain to where you store memories, and so you’re saying there’s a strong overlap between the two?

Andy - Exactly right. Another account is that odours, at least at a perceptual level, are thought to be a single feature stimulus so it’s a lot easier for odours to associate with events compared to say for example of a visual stimulus, which is made of lots of different components.

Chris - Now, we were talking earlier to Matthew Cobb who was explaining that when I smell something, a whole constellation of different odorant chemicals goes up my nose and binds onto nerve endings at the top of my nose, activates those nerve endings, and these are then used to drive different parts of the brain and a sort of ‘smell fingerprint pattern’ is established in my brain. So how do I actually remember then what smell is what?

Andy - There is one account that uses this kind of configuration or pattern of receptors that are activated. It’s been suggested that within the olfactory cortex, you might process and then store this particular pattern of receptors that have been activated by a specific odour. And when we’re exposed to an odour we then kind of crosscheck or reference the current pattern or configuration with that which is stored within our memory.

However, once we’ve made that kind of familiarity judgement, once we’ve gone okay, I think there’s a match and this odour is familiar, we’re actually very bad and then going on to identify what that odour is. One of the possible reasons for that is an evolutionary one in that we didn’t really need to be able to identify odours because it was a close or near sense where we were essentially making a good/bad judgement typically about food; whether we spit or whether we swallow and, therefore, being able to identify the odour wasn’t really necessary.

Chris - What are the studies that you’re doing to try and understand how smell and memory are linked?

Andy - Our main focus is to look at the extent to which smell memory, or short term memory for odours works in a similar way to other types of stimuli, so we’re examining evidence that smell memory is in some way different. Looking at odour memory is fraught with quite a few challenges. The first thing is when you’re looking at smell memory, what you really want to be measuring is ‘smell memory,’ which might sound kind of obvious but the default strategy that people use in memory tasks is to try and verbalise. They’ll always try and assign a verbal label to those odours to make it easier so we initially have to try and make that harder by our selection of odours, and also by giving them secondary tasks to do that might use up their verbal systems. We have to try and change some of the existing memory tasks which are kind of weighted heavily towards verbal memory so that they can be applied to odours.

Chris - What have you found so far?

Andy - Invariably the answer is “it depends”, and that’s the same with our works. On some studies we find that odour memory works in a very similar way to say visual and verbal memory. In other times it seems to be a bit different so we have these mixed findings. One of the possible explanations for that is we see, across the literature generally, a lack of control over the odours that people are using in this research. And there is some evidence to suggest that we process nameable and hard-to-name odours differently. There’s an imaging study showing that different parts of the brain are activated for odours that are easy to name compared to odours that are hard to name.

Chris - And why does this matter; why is this important, Andy, that you’re able to put a finger on this?

Andy - Personally, I think it’s interesting because we don’t know much about smell memory relative to other senses, but I appreciate everyone is not as exciting as me. The other kind of big exciting element of our memory is that it’s been shown, to some extent, to be predictive of Alzheimer’s onset. There is a study that examines people with a very rare gene that looks at early onset Alzheimer’s, and people who have that gene have been shown to be poorer at odour recognition even though they don’t show any other clinical signs. There’s other studies also looking at people with mild cognitive impairment, so not an uncommon feature of getting older and those people with poor odour identification were at higher risk of developing Alzheimer’s later down the line.

Chris - So you could potentially use this as maybe a screening test to see who might be at risk of things like dementia?

Andy - To some extent, but it’s important will all the kind of predictive studies, the biggest predictor of dementia is old age so that kind of accounts for the vast amount of the variants.