Smell, taste and your brain: How are they linked together?

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The official term olfactory memory refers to the sense of smell triggering vivid memories. Have you ever wondered why this is the case?

Smell is handled by the olfactory bulb in the front of our brains. The olfactory bulb sends information to the other areas of the body’s central command for it to be processed further. Odours take a direct route to the limbic system which includes amygdala and hippocampus, both regions which are related to memory. Odours passing through the limbic system will therefore associate with a memory linking the two together. This is why when you smell that perfume, you think of a certain person or location. In the world of business, this can be used to make people remember of certain places when they smell a particular scent. For example, a specific hotel will be pumped with an odour that is unique to its chain i.e Hilton, reminding people that they are present in that place.1

Smell can also be linked to different emotions. As previously mentioned, perfumes are built around this connection to emotions, with fragrances being developed to convey multiple emotions, from desire to relaxation. Different people have different perceptions of different smells. Some smells can also be repugnant and are this way because they warn us of danger such as food being rotten or smoke.2

Recently there has been a discovery that could potentially allow improved smell tests for Alzheimer’s disease diagnosis. Neurobiologists at the University of Toronto have identified a mechanism permitting the brain to recreate past experiences from memory. The ante-rior olfactory nucleus (AON) is poorly understood and upon further research of the AON, researchers found a previously unknown pathway between the hippocampus and it. This pathway is critical for memory and highly implicated in Alzheimer’s disease. By cutting this pathway, they could mimic the problem seen in people in Alzheimer’s disease. In mice, those that did not have the AON-hippocampus pathway disconnected smelt for a longer period of time to try and remember the origin of the odour. In Alzheimer’s disease patients, the AON degenerates early on in life suggesting that the ‘when’ and ‘where’ odours were encountered. The study could be the start of a better understanding of Alzheimer’s disease.3

Given the manner in which smell is entangled with our emotions, the loss of smell can have a detrimental effect on humans. Anosmia sufferers often say that they feel ‘isolated’ and ‘cut-off’ from the world around them. Smell loss can affect one’s ability to form and maintain close personal relationships which could also lead to depression. It could also signal something a lot more serious such as Alzheimer’s disease and Parkinson’s disease, as well as more recently, COVID-19, where loss of smell has been added to the list of symptoms.2

Smell is clearly a very powerful sense and has even been suggested to help improve memory. A couple of years ago, researchers suggest that pupils who work in a room with the aroma of rosemary, in the form of essential oil, 5% to 7% better results in memory. Rosemary has always been associated with memory with Ancient Greek students wearing garlands of rosemary in exams and Ophelia in Shakespeare’s Hamlet even quoting “There’s rosemary, that’s for remembrance.”4

Rosemary oil contains compounds such as 1,8-cineole, which causes an increase in a neurotransmitter called acetylcholine. This prevents the breakdown of the neurotransmitter by an enzyme. This is highly plausible because with inhalation, small molecules pass straight into the bloodstream and from there into the brain without being broken down by the liver like a normal drug would5.

Smell is also highly important in tasting different foods and drink. Taste receptors are present on the front and back of the tongue as well as on the sides, back and roof of the mouth. These cells bind with molecules from food being eaten and sends signals to the brain. Flavour of food and drink is the result of olfactory neurones at the top of our nasal cavity detecting molecules of the food we are eating. This is why anosmia sufferers do not want to eat food as much as they cannot smell it. You do not look forward to eating something and this could lead to malnutrition as you may not feel the need to eat unless you are hungry, something anosmia sufferers must rely on to tell them when it is time to eat.6


References

  1. Colleen Walsh, What the nose knows, The Harvard Gazette, February 27th 2020
  2. Psychology and Smell, Fifth Sense, https://www.fifthsense.org.uk/psychology-and-smell/
  3. Scientists uncover new connection between smell and memory, Science Daily, https://www.sciencedaily.com/releases/2018/07/180723155726.htm
  4. Sean Coughlan, Exam revision students ‘should smell rosemary for memory’, BBC News, 4 May 2017
  5. What does rosemary do to your brain?, BBC News, 15 July 2015
  6. Smell, Taste and Flavour, Fifth Sense,https://www.fifthsense.org.uk/smell-taste-and-flavour/

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