New research reveals there’s more to our tongues than we may have thought

Fifth Sense recently heard about an interesting research project that investigated the role our tongues play in taste perception.

Scientists from the Monell Chemical Senses Center in Philadelphia report that functional olfactory receptors – the sensors that detect odours in the nose – are also present in taste cells found on the human tongue. By studying cultures of these taste cells, the scientists discovered that they responded to odour molecules in a manner similar to olfactory receptors in the nose.

With regards to eating, it has long been known that the brain processes information received independently from the tongue (taste) and retro-nasally via the nose (smell). In combination, this information contributes to our assessment of the food in our mouths – including what we know as flavour. Monell’s research suggests that something more may be going on, that interactions between the senses of smell and taste are also happening on the tongue.

Fifth Sense member and Communications Advisor, Max Law, was keen to learn more. What exactly do these findings mean?  Might Fifth Sense members be the beneficiaries of this and future research into the tongue? Max caught up with the leading scientist on the Monell team, Dr Mehmet Hakan Ozdener, to find out.

Max Law: The majority of our members lack a properly functioning sense of smell which of course impacts their ability to enjoy flavour in food. What words of encouragement can you offer them with regard to your findings? 

Dr Ozdener: My data demonstrate that olfactory receptors are present in taste cells. However, I do not know how these olfactory receptors are wired to the brain. Olfactory receptors are located on taste cells and when taste cells are stimulated, they activate areas of the brain that give us the sensations of taste: i.e. bitter, sour, sweet, savoury and salty. So, I believe that olfactory receptors in taste cells may have a modulatory role on taste perception in the mouth. That is, odour molecules may enhance/reduce/eliminate certain tastes of food. For example, it is well known that the odour of vanilla can enhance the sweetness of a food or beverage. 

Max Law: It would be wonderful if Fifth Sense members might one day be pointed towards foods or drinks known to be richest in the molecules that activate odour receptors on the tongue. Might it be possible for research to identify such molecules and if so, are there any plans to do so?

Dr Ozdener: My work on the function of olfactory receptors located in taste cells is new and ongoing. There are many challenging questions to address, including the ones you raise. At this time, we understand very little about which odours stimulate the olfactory receptors on the tongue and how these ‘tongue odours’ may affect our sensory perception and enjoyment of food.

Max Law: We often hear from members concerned about the impact their anosmia is having on dietary choices. A fair number seem to gravitate towards foods high in sugar and salt. It’s only anecdotal, yet one wonders if such people are at higher risk than the general population. With this in mind, might they one day be able to satisfy their cravings in other, healthier ways?  

Dr Ozdener: As you and the members of Fifth Sense are well aware, the odour of foods is very important to overall food perception and acceptance. Food odour and taste combine to produce food flavours. There is much interaction between taste and smell. We know that certain odours can enhance the perceived sweetness and saltiness of foods and reduce perceived bitterness. Without the sensory enhancement of taste from food odours, it may be the case that anosmics are more inclined to choose foods higher in salt and sugar. However, it is too early to predict whether we will be able to harness information from odours detected by the tongue to redirect flavour perception or preferences.

Max Law: We were fascinated to learn that your study was based on human taste cells grown in cultured environments. Fifth Sense partners with an organisation called FlavorActiV, the world leader in the training and monitoring of professional tasting panels. We are presently working with FlavorActiv on a taste training project aimed at helping people affected by olfactory loss make the best use of any remaining sense of taste. It prompts us to wonder whether there any plans, or is there any value, in using human subjects in future, tongue-related research? Could people with anosmia be helpful in this regard? Our experience suggests that many of us with no noses are very in tune with our tongues!

Dr Ozdener: It certainly is of interest to contrast the olfactory function of taste receptors on the tongue in anosmic vs. non-anosmic populations. One might expect that the olfactory receptors on the tongue would function normally in anosmics who lost their sense of smell from conditions affecting the nasal cavity, for example from a viral infection. On the other hand, it may be that those who were born without a sense of smell may also not have functional olfactory receptors on the tongue. We simply don’t know the answers to these questions at this time.

So, what are we to make of all this?

With an impaired sense of smell, we’ve learnt to treasure our tongues as the gateway to what we have left. We’re never going to smell by sticking out our tongues, but it’s encouraging that they appear to be doing more than we knew.

Odours we pick up from our tongues seem to affect how we perceive the likes of saltiness, sweetness etc. This could be why some of us can still differentiate between certain foods or drinks, even when flavour is absent. For example, why some can evaluate the different ‘bitternesses’ of coffee or real ale.

Yet the senses of smell and taste operate in highly complex and multi-variate ways. Their precise workings are hard to pin down. Fifth Sense trustee and ENT consultant, Professor Carl Philpott summed it up:

“At this stage it’s too early to draw any significant conclusions from this research. We don’t know how olfactory receptors work on the tongue, and although the research does suggest a possible mechanism, we would need a further study to prove this.”

By revealing new things about smell and taste, Dr Ozdener’s work shows how much there is that we still don’t know. Nevertheless, Monell and Dr Ozdener should be applauded for a project that signposts where the world of science might look next for answers. Fifth Sense will follow such developments with interest.