During the pandemic, a lost sense of smell was quickly identified as one of the key symptoms of COVID. Nearly four years later, one in five people in the UK is living with a decreased or distorted sense of smell, and one in twenty have anosmia – the total loss of the ability to perceive any odours at all. Smell training is one of the few treatment options for recovering a lost sense of smell – but can we make it more effective?

Smell training is a therapy that is recommended by experts for recovering a lost sense of smell. It is a simple process that involves sniffing a set of different odours – usually essential oils, or herbs and spices – every day.

The olfactory system has a unique ability to regenerate sensory neurons (nerve cells). So, just like physiotherapy where exercise helps to restore movement and function following an injury, repeated exposure to odours helps to recover the sense of smell following an infection, or other cause of smell loss (for example, traumatic head injury).

Several studies have demonstrated the effectiveness of smell training under laboratory conditions. But recent findings have suggested that the real-world results might be disappointing.

One reason for this is that smell training is a long-term therapy. It can take months before patients detect anything, and some people may not get any benefit at all.

In one study, researchers found that after three months of smell training, participation dropped to 88%, and further declined to 56% after six months. The reason given was that these people did not feel as though they noticed any improvement in their ability to smell.

Cross-modal associations

To remedy this, researchers are now investigating how smell training can be improved. One interesting idea is that information from our other senses, or “cross-modal associations”, can be applied to smell training to promote odour perception and improve the results.

Cross-modal associations are described as the tendency for sensory cues from different sensory systems to be matched. For example, brightness tends to be associated with loudness. Pitch is related to size. Colours are linked to temperature, and softness is matched with round shapes, while spiky shapes feel more rough. In previous studies, these associations have been shown to have a considerable influence on how sensory information is processed. Especially when it comes to olfaction.

Recent research has shown that the sense of smell is influenced by a combination of different sensory inputs – not just odours. Sensory cues such as colour, shape, and pitch are believed to play a role in the ability to correctly identify and name odours, and can influence perceptions of odour pleasantness and intensity.

In one study, participants were asked to complete a test that measured their ability to discriminate between different odours while they were presented with the colour red or yellow, an outline drawing of a strawberry or a lemon, or a combination of these colours and shapes. The results suggested that corresponding odour and colour associations (for example, the colour red and strawberry) were linked to increased olfactory performance compared with odours and colours that were not associated (for example, the colour yellow and strawberry).

While projects focusing on harnessing these cross-modal associations to improve treatments for smell loss are underway, research has already started to deliver some promising results.

In a recent study that aimed to investigate whether the effects of smell training could be improved with the addition of cross-modal associations, participants watched a guidance video containing sounds that matched the odours that they were training with. The results suggest that cross-modal interactions plus smell training improved olfactory function compared to smell training alone.

The results reported in recent studies have been promising and offer new insights into the field of olfactory science. It is hoped that this will soon lead to the development of more effective treatment options for smell recovery.

In the meantime, smell training is one of the best things you can do for a lost sense of smell, so patients are encouraged to stick with it so that they give themselves the best chance at recovery.

Emily Spencer, PhD Candidate, Olfaction, Edinburgh Napier University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Pratik Raul, University of Canberra; Jeroen van Boxtel, University of Canberra, and Jovana Acevska, University of Canberra

Autism is a neurodevelopmental difference associated with specific experiences and characteristics.

For decades, autism research has focused on behavioural, cognitive, social and communication difficulties. These studies highlighted how autistic people face issues with everyday tasks that allistic (meaning non-autistic) people do not. Some difficulties may include recognising emotions or social cues.

But some research, including our own study, has explored specific advantages in autism. Studies have shown that in some cognitive tasks, autistic people perform better than allistic people. Autistic people may have greater success in identifying a simple shape embedded within a more complex design, arranging blocks of different shapes and colours, or spotting an object within a cluttered visual environment (similar to Where’s Wally?). Such enhanced performance has been recorded in babies as young as nine months who show emerging signs of autism.

How and why do autistic individuals do so well on these tasks? The answer may be surprising: more “neural noise”.

What is neural noise?

Generally, when you think of noise, you probably think of auditory noise, the ups and downs in the amplitude of sound frequencies we hear.

A similar thing happens in the brain with random fluctuations in neural activity. This is called neural noise.

This noise is always present, and comes on top of any brain activity caused by things we see, hear, smell and touch. This means that in the brain, an identical stimulus that is presented multiple times won’t cause exactly the same activity. Sometimes the brain is more active, sometimes less. In fact, even the response to a single stimulus or event will fluctuate continuously.

Neural noise in autism

There are many sources of neural noise in the brain. These include how the neurons become excited and calm again, changes in attention and arousal levels, and biochemical processes at the cellular level, among others. An allistic brain has mechanisms to manage and use this noise. For instance, cells in the hippocampus (the brain’s memory system) can make use of neural noise to enhance memory encoding and recall.

Evidence for high neural noise in autism can be seen in electroencephalography (EEG) recordings, where increased levels of neural fluctuations were observed in autistic children. This means their neural activity is less predictable, showing a wider range of activity (higher ups and downs) in response to the same stimulus.

In simple terms, if we imagine the EEG responses like a sound wave, we would expect to see small ups and downs (amplitude) in allistic brains each time they encounter a stimulus. But autistic brains seem to show bigger ups and downs, demonstrating greater amplitude of neural noise.

Many studies have linked this noisy autistic brain with cognitive, social and behavioural difficulties.

But could noise be a bonus?

The diagnosis of autism has a long clinical history. A shift from the medical to a more social model has also seen advocacy for it to be reframed as a difference, rather than a disorder or deficit. This change has also entered autism research. Neuroaffirming research can examine the uniqueness and strengths of neurodivergence.

Psychology and perception researcher David Simmons and colleagues at the University of Glasgow were the first to suggest that while high neural noise is generally a disadvantage in autism, it can sometimes provide benefits due to a phenomenon called stochastic resonance. This is where optimal amounts of noise can enhance performance. In line with this theory, high neural noise in the autistic brain might enhance performance for some cognitive tasks.

Our 2023 research explores this idea. We recruited participants from the general population and investigated their performance on letter-detection tasks. At the same time, we measured their level of autistic traits.

We performed two letter-detection experiments (one in a lab and one online) where participants had to identify a letter when displayed among background visual static of various intensities.

By using the static, we added additional visual noise to the neural noise already present in our participants’ brains. We hypothesised the visual noise would push participants with low internal brain noise (or low autistic traits) to perform better (as suggested by previous research on stochastic resonance). The more interesting prediction was that noise would not help individuals who already had a lot of brain noise (that is, those with high autistic traits), because their own neural noise already ensured optimal performance.

Indeed, one of our experiments showed people with high neural noise (high autistic traits) did not benefit from additional noise. Moreover, they showed superior performance (greater accuracy) relative to people with low neural noise when the added visual static was low. This suggests their own neural noise already caused a natural stochastic resonance effect, resulting in better performance.

It is important to note we did not include clinically diagnosed autistic participants, but overall, we showed the theory of enhanced performance due to stochastic resonance in autism has merits.

Why this is important?

Autistic people face ignorance, prejudice and discrimination that can harm wellbeing. Poor mental and physical health, reduced social connections and increased “camouflaging” of autistic traits are some of the negative impacts that autistic people face.

So, research underlining and investigating the strengths inherent in autism can help reduce stigma, allow autistic people to be themselves and acknowledge autistic people do not require “fixing”.

The autistic brain is different. It comes with limitations, but it also has its strengths.

Pratik Raul, PhD candidiate, University of Canberra; Jeroen van Boxtel, Associate professor, University of Canberra, and Jovana Acevska, Honours Graduate Student, University of Canberra

This article is republished from The Conversation under a Creative Commons license. Read the original article.