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What happens in your brain when you cannot smell

Professor Johan Lundstrom leads the way in understanding how our brain processes smell and he shared with Chrissi the implications of what he has learned for successful smell training.

Johan Lundstrom is an Associate Professor at the Department of Clinical Neuroscience, Karolinska Institutet (Stockholm, Sweden) and an Associate Member at the Monell Chemical Senses Center. His research looks closely at all the different areas of the brain involved in olfaction, the process of smelling.

The structure of the brain is capable of change throughout our lives, building and rebuilding connections and abilities to perform different tasks, responding to our life experiences. Johan was curious to see what differences there are between the brain of someone born without the ability to smell - congenital anosmia - and the brain of someone who had lost their sense of smell  - acquired anosmia.

At first look, there appeared to be very little difference. The main difference is that the primary smell processing equipment - the olfactory bulb - is usually absent in someone born without smell, and can be seen to reduce in size when someone loses smell (and increase with exercise like smell training). However, smell is processed across many different parts of the brain simultaneously, and those other areas all seemed to be the same.

When Johan and his team started to look at the way the brain is networked, things were very different. They recognised that one particular part of the brain is not dedicated to one sense, but can be used to process multiple senses: sight and sound and smell can all be processed by the same area. When smell was lost and that part became redundant, other sensory functions moved in and the brain adjusted to do more seeing and listening instead.

Johan’s findings suggest that acquired anosmia leads to changes in all the parts of the brain associated with smell. This means that to recover smell, the function has to be rebuilt across many different moving parts.

What does this mean for smell training?

For Johan, these changes underline the need to start smell training early as it's hard to reprogramme areas once they have been taken over by other sensory functions. By early, he means as soon as possible after the smell has been lost, but six to 12 months after loss is still early enough to make a positive difference to recovery. 

“Olfactory training is a slog,” he told Chrissi in the webinar, “but give up early and you won’t see any benefit.” Making changes to the brain is slow and actions need to be repetitive to take effect. To smell train for a few weeks then stop because it’s not making a difference is like going to the gym a few times and expecting to lose 20 pounds in weight.

Johan’s knowledge of the way the brain functions suggests that smell training makes recovery more stable and develops a richer experience of smell. He suggests that any sensory input [smell training] will be an improvement, but it’s not a cure. Like physio for a broken leg, it will rebuild strength over time, but you might not be able to run marathons.

This conversation is taken from AbScent Presents: Smell loss - what's happening at a deeper level, recorded on 16 November 2021. Watch the webinar on the AbScent YouTube channel.

December 07, 2021