tag:theconversation.com,2011:/africa/topics/sense-of-taste-42345/articlesSense of taste – The Conversation2022-05-23T19:58:09Ztag:theconversation.com,2011:article/1827552022-05-23T19:58:09Z2022-05-23T19:58:09ZCOVID made things taste weird, now ‘Paxlovid mouth’ sounds disgusting. What causes dysgeusia?<figure><img src="https://images.theconversation.com/files/463882/original/file-20220518-17-45x5bz.jpg?ixlib=rb-1.1.0&rect=17%2C25%2C5737%2C3804&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://image.shutterstock.com/image-photo/closeup-image-asian-woman-holding-600w-659054242.jpg">Shutterstock</a></span></figcaption></figure><p>Loss or alteration of taste (dysgeusia) is a common symptom of COVID. It’s also a side effect of several illnesses and medications, including Paxlovid, the new antiviral medication to treat COVID infection. </p>
<p>Although it affects fewer than 6% of people who are given Paxlovid, some <a href="https://www.theatlantic.com/health/archive/2022/05/pfizer-paxlovid-covid-pill-side-effects/629772/">report</a> a “horrible” taste that came on soon after they started taking the drug. </p>
<p>Dysgeusia is described as a bitter, metallic or sour taste in the mouth. But what exactly is it, and what’s going on in the body when it happens?</p>
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Read more:
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<h2>What happens in the brain when we taste?</h2>
<p>Aside from the pleasure we get from eating food that tastes good, our sense of taste also serves other purposes. Taste helps us <a href="https://www.sciencedirect.com/science/article/pii/S0960982213004181">decide what to eat</a>, ensuring we get enough nutrients and energy. It also helps us metabolise the foods we have eaten. </p>
<p>Our sense of taste can also keep us safe from consuming things that are dangerous to our health, such as poisons or food which has spoilt. </p>
<p>There are around <a href="https://jamanetwork.com/journals/jamaneurology/fullarticle/784121">10,000 taste buds</a> in the human mouth, with each taste bud having up to 150 taste receptors. These taste receptors on our taste buds help detect whether food is salty, sweet, bitter, sour or <a href="https://www.theguardian.com/lifeandstyle/wordofmouth/2013/apr/09/umami-fifth-taste">umami</a>. </p>
<p>Taste buds transmit information to the brain about what we’re eating through several <a href="https://jamanetwork.com/journals/jamaneurology/fullarticle/784121">nerve pathways</a>. </p>
<p>Information about taste is first transmitted to the brain stem at the base of the brain, and is then sent throughout the brain via connected pathways, reaching the <a href="https://pubmed.ncbi.nlm.nih.gov/15134840/">orbitofrontal cortex</a> at the front of the brain. This area <a href="https://neuroscientificallychallenged.com/posts/know-your-brain-orbitofrontal-cortex#:%7E:text=The%20orbitofrontal%20cortex%20is%20the,involved%20in%20emotion%20and%20memory.">connects</a> to sensory areas and the limbic system that helps encode memory and emotion. </p>
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<a href="https://images.theconversation.com/files/463878/original/file-20220518-19-qrjnb6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="microscopic view of taste buds" src="https://images.theconversation.com/files/463878/original/file-20220518-19-qrjnb6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/463878/original/file-20220518-19-qrjnb6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/463878/original/file-20220518-19-qrjnb6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/463878/original/file-20220518-19-qrjnb6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/463878/original/file-20220518-19-qrjnb6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/463878/original/file-20220518-19-qrjnb6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/463878/original/file-20220518-19-qrjnb6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Taste buds, up close.</span>
<span class="attribution"><a class="source" href="https://image.shutterstock.com/image-photo/taste-buds-foliate-tongue-papillae-600w-418975864.jpg">Shutterstock</a></span>
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Read more:
<a href="https://theconversation.com/four-strange-covid-symptoms-you-might-not-have-heard-about-181217">Four strange COVID symptoms you might not have heard about</a>
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<h2>3 causes of dysgeusia</h2>
<p>Aside from direct damage to the tongue and mouth, dysgeusia can be caused by <a href="https://jamanetwork.com/journals/jamaneurology/fullarticle/784121">several factors</a>: infection or disease, medicines, or damage to the central nervous system.</p>
<p><strong>1. Infection or disease</strong></p>
<p>Alterations in taste have been reported after <a href="https://www.sciencedirect.com/science/article/pii/S019607091300104X">influenza</a> infection, in hayfever, diabetes, heart disease and <a href="https://www.oooojournal.net/article/S2212-4403(20)31075-0/fulltext">others</a>.</p>
<p>Today, one of the most frequent causes of dysgeusia is <a href="https://www.frontiersin.org/articles/10.3389/fcimb.2021.716563/full">COVID</a>, with loss of taste one of the first <a href="https://academic.oup.com/chemse/article/45/7/609/5860460#321424546">symptoms</a> many people experience. Research suggests dysgeusia occurs in between <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7308993/">33%</a> and <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7199692/">50%</a> of people with COVID, though less so with <a href="https://www.webmd.com/lung/news/20220511/smell-taste-loss-less-likely-with-newer-covid-variants-study#1">newer variants</a>. It’s also been <a href="https://www.frontiersin.org/articles/10.3389/fcimb.2021.716563/full">reported</a> as a lingering symptom of Long COVID.</p>
<p>Scientists don’t know exactly why COVID or other infections cause dysgeusia. Some recent theories centre on how the SARS-CoV-2 virus that causes COVID triggers an inflammatory response by binding to receptors in the mouth. This might cause changes in <a href="https://www.oooojournal.net/article/S2212-4403(20)31075-0/fulltext">molecular and cellular pathways</a> which could alter taste. </p>
<p>Because of the close links between taste and smell, <a href="https://europepmc.org/article/NBK/nbk554522">viral-induced damage</a> to the lining of the nose may be enough to cause taste disturbance. </p>
<p>The virus could also be causing more direct damage to taste buds, nerves involved in taste, or brain areas responsible for taste <a href="https://www.oooojournal.net/article/S2212-4403(20)31075-0/fulltext">sensory processing</a>. </p>
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<a href="https://images.theconversation.com/files/463879/original/file-20220518-25-klwv89.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="sick woman sniffs orange" src="https://images.theconversation.com/files/463879/original/file-20220518-25-klwv89.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/463879/original/file-20220518-25-klwv89.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/463879/original/file-20220518-25-klwv89.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/463879/original/file-20220518-25-klwv89.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/463879/original/file-20220518-25-klwv89.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/463879/original/file-20220518-25-klwv89.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/463879/original/file-20220518-25-klwv89.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Disruptions to the nose and sense of smell can also affect taste.</span>
<span class="attribution"><a class="source" href="https://image.shutterstock.com/image-photo/sick-woman-trying-sense-smell-600w-1899077899.jpg">Shutterstock</a></span>
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<p><strong>2. Injury</strong></p>
<p>Loss of taste can also follow <a href="https://www.amjmed.com/article/S0002-9343(11)00165-3/fulltext">damage to the nerves and brain pathways</a> involved in taste perception. </p>
<p>This could be because of lesions in the nerves or brain tissue, or could be due to loss of the fatty myelin coating which helps insulate the pathways used for taste signalling. In rare cases, dysgeusia can also be due to brain tumours. </p>
<p><strong>3. Medications</strong></p>
<p>Dysgeusia is a known side effect of several medications, including antibiotics and medications for Parkinson’s disease, epilepsy and HIV. </p>
<p>There could be several reasons for this. The medications themselves may have a bitter taste which lingers in our taste buds. </p>
<p>Medications can also activate specific taste receptors that detect bitter, sour or metallic flavours, activating these taste receptors in a way that we don’t often experience with our food.</p>
<p>The new antiviral medication <a href="https://www.nejm.org/doi/full/10.1056/NEJMoa2118542">Paxlovid</a> is almost 90% effective at reducing COVID hospitalisations and deaths. </p>
<p>However, dysgeusia is a prominent side effect of Paxlovid. Although it occurs in less than 6% of people, dysgeusia has been nicknamed “<a href="https://www.health.com/condition/infectious-diseases/coronavirus/what-is-paxlovid-mouth-bitter-metallic-taste-side-effects">Paxlovid mouth</a>”.</p>
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Read more:
<a href="https://theconversation.com/australia-approves-two-new-medicines-in-the-fight-against-covid-how-can-you-get-them-and-are-they-effective-against-omicron-175321">Australia approves two new medicines in the fight against COVID. How can you get them and are they effective against Omicron?</a>
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<p><a href="https://www.tga.gov.au/sites/default/files/paxlovid-pi.pdf">Paxlovid</a> is actually two medications: nirmatrelvir and ritonavir. Nirmatrelvir is the main antiviral drug to combat COVID, and Ritonavir is given <a href="https://www.prn.org/index.php/management/article/pharmacokinetic_boosting_of_protease_inhibitors_298">at the same time</a> to stop nirmatrelvir being broken down too quickly, so it can remain active in the body for longer. </p>
<p><a href="https://pubmed.ncbi.nlm.nih.gov/10501290/">Ritonavir</a> has a bitter taste and causes dysgeusia when taken alone or in combination with other medications. Although the mechanism has not been researched, Ritonavir could be the underlying factor behind Paxlovid mouth. </p>
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<h2>Leaving a bad taste</h2>
<p>While it can be unpleasant, dysgeusia is usually short-lived, and should improve after medications are finished or infection is resolved. </p>
<p>People who experience prolonged changes in taste should seek medical assessment to determine the underlying cause. In the short term, lozenges, mints and salt water gargles may make dysgeusia more manageable. Although it may be an unpleasant size effect of Paxlovid, short-term dysgeusia is a palatable trade-off to reduce the serverity of COVID infection.</p><img src="https://counter.theconversation.com/content/182755/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sarah Hellewell does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The effects of COVID and a new treatment for it are leaving a bad taste in the mouth for many. How do we detect what’s salty, sweet, bitter, sour or umami?Sarah Hellewell, Research Fellow, Faculty of Health Sciences, Curtin University, and The Perron Institute for Neurological and Translational Science, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1784992022-03-07T20:56:11Z2022-03-07T20:56:11ZEven mild cases of COVID-19 can leave a mark on the brain, such as reductions in gray matter – a neuroscientist explains emerging research<figure><img src="https://images.theconversation.com/files/449924/original/file-20220303-8225-6rnqah.jpg?ixlib=rb-1.1.0&rect=116%2C44%2C5874%2C3943&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A new brain-imaging study finds that participants who had even mild COVID-19 showed an average reduction in whole brain sizes.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/medical-background-of-healthy-brain-and-diseased-royalty-free-image/1365700653?adppopup=true">Kirstypargeter/iStock via Getty Images Plus</a></span></figcaption></figure><p>Researchers have been steadily gathering important insights into the effects of COVID-19 on the body and brain. Two years into the pandemic, these findings are raising concerns about the long-term impacts the coronavirus might have on biological processes such as aging. </p>
<p>As a <a href="https://scholar.google.com/citations?user=By7qto8AAAAJ&hl=en">cognitive neuroscientist</a>, I have focused in <a href="https://liberalarts.tamu.edu/psychology/profile/jessica-bernard/">my past research</a> on understanding how normal brain changes related to aging affect people’s ability to think and move – particularly in middle age and beyond. </p>
<p>But as evidence came in showing that COVID-19 could affect <a href="https://theconversation.com/deciphering-the-symptoms-of-long-covid-19-is-slow-and-painstaking-for-both-sufferers-and-their-physicians-164754">the body and brain</a> for months following infection, my research team shifted some of its focus to better understanding how the illness might influence the natural process of aging. This was motivated in large part by compelling new work from the United Kingdom investigating the impact of COVID-19 on the human brain. </p>
<h2>Peering in at the brain’s response to COVID-19</h2>
<p>In a large study published in the journal Nature on March 7, 2022, a team of researchers in the UK <a href="https://doi.org/10.1038/s41586-022-04569-5">investigated brain changes in people ages 51 to 81</a> who had experienced COVID-19. This work provides important new insights about the impact of COVID-19 on the human brain. </p>
<p>In the study, researchers relied on a database called the <a href="https://www.ukbiobank.ac.uk/">UK Biobank</a>, which contains brain imaging data from over 45,000 people in the <a href="https://doi.org/10.1038/s41467-020-15948-9">U.K. going back to 2014</a>. This means that there was baseline data and brain imaging of all of those people from before the pandemic. </p>
<p>The research team compared people who had experienced COVID-19 with participants who had not, carefully matching the groups based on age, sex, baseline test date and study location, as well as common risk factors for disease, such as health variables and socioeconomic status. </p>
<p>The team found marked differences in gray matter – or the neurons that process information in the brain – between those who had been infected with COVID-19 and those who had not. Specifically, the thickness of the gray matter tissue in brain regions known as the frontal and temporal lobes was reduced in the COVID-19 group, differing from the typical patterns seen in the people who hadn’t had a COVID-19 infection. </p>
<p>In the general population, it is normal to see some change in gray matter volume or thickness over time as people age. But the changes were more extensive than normal in those who had been infected with COVID-19.</p>
<p>Interestingly, when the researchers separated the individuals who had severe enough illness to require hospitalization, the results were the same as for those who had experienced milder COVID-19. That is, people who had been infected with COVID-19 showed a loss of brain volume even when the disease was not severe enough to require hospitalization.</p>
<p>Finally, researchers also investigated changes in performance on cognitive tasks and found that those who had contracted COVID-19 were slower in processing information than those who had not. This processing ability was correlated with volume in a region of the brain known as the cerebellum, indicating a link between brain tissue volume and cognitive performance in those with COVID-19. </p>
<p>This study is particularly valuable and insightful because of its large sample sizes both before and after illness in the same people, as well as its careful matching with people who had not had COVID-19. </p>
<h2>What do these changes in brain volume mean?</h2>
<p>Early on in the pandemic, one of the most common reports from those infected with COVID-19 was the loss of <a href="https://doi.org/10.1038/s41591-020-0916-2">sense of taste and smell</a>. </p>
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<img alt="A woman with COVID-19 symptoms tries to sense the smell of a fresh tangerine." src="https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Some people with COVID-19 have experienced either the loss of, or a reduction in, their sense of smell.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/sick-woman-trying-to-sense-smell-of-fresh-tangerine-royalty-free-image/1298987743?adppopup=true">Dima Berlin via Getty Images</a></span>
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<p>Strikingly, the brain regions that the U.K. researchers found to be affected by COVID-19 are all linked to the olfactory bulb, a structure near the front of the brain that passes signals about smells from the nose to other brain regions. The olfactory bulb has connections to regions of the temporal lobe. Researchers often talk about the temporal lobe in the context of aging and Alzheimer’s disease, because it is <a href="https://doi.org/10.1073/pnas.1801093115">where the hippocampus</a> is located. The hippocampus is likely to play a key role in aging, given its involvement in memory and cognitive processes. </p>
<p>The sense of smell is also important to Alzheimer’s research, as some data has suggested that those at risk for the disease <a href="https://doi.org/10.1016/S0197-4580(01)00337-2">have a reduced sense of smell</a>. While it is too early to draw any conclusions about the long-term impacts of COVID-related effects on the sense of smell, investigating possible connections between COVID-19-related brain changes and memory is of great interest – particularly given the regions implicated and their importance in memory and Alzheimer’s disease. </p>
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<figcaption><span class="caption">An overview of how our sense of smell is connected to receptors in the brain.</span></figcaption>
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<p>The study also highlights a potentially important role for the cerebellum, an area of the brain that is involved in cognitive and motor processes; importantly, <a href="https://doi.org/10.1016/j.neubiorev.2014.02.011">it too is affected in aging</a>. There is also an emerging line of work <a href="https://doi.org/10.1093/brain/awx257">implicating the cerebellum in Alzheimer’s</a> disease. </p>
<h2>Looking ahead</h2>
<p>These new findings bring about important yet unanswered questions: What do these brain changes following COVID-19 mean for the process and pace of aging? Also, does the brain recover from viral infection over time, and to what extent? </p>
<p>These are active and open areas of research we are beginning to tackle in my laboratory in conjunction with our ongoing work investigating brain aging. </p>
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<a href="https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Brain scans from a person in their 30s and a person in their 80s, showing reduced brain volume in the older adult brain" src="https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=576&fit=crop&dpr=1 600w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=576&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=576&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=724&fit=crop&dpr=1 754w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=724&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=724&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Brain images from a 35-year-old and an 85-year-old. Orange arrows show the thinner gray matter in the older individual. Green arrows point to areas where there is more space filled with cerebrospinal fluid (CSF) due to reduced brain volume. The purple circles highlight the brains’ ventricles, which are filled with CSF. In older adults, these fluid-filled areas are much larger.</span>
<span class="attribution"><span class="source">Jessica Bernard</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Our lab’s work demonstrates that as people age, the brain thinks and <a href="https://doi.org/10.1093/geronb/gbaa005">processes information differently</a>. In addition, we’ve observed changes over time in how <a href="https://doi.org/10.1016/j.neubiorev.2009.10.005">people’s bodies move</a> and how people learn new motor skills. Several <a href="https://doi.org/10.31887/DCNS.2001.3.3/dcpark">decades of work</a> have demonstrated that older adults have a harder time processing and manipulating information – such as updating a mental grocery list – but they typically maintain their knowledge of facts and vocabulary. With respect to motor skills, we know that <a href="https://doi.org/10.1016/j.neuropsychologia.2020.107620">older adults still learn</a>, but they do so more <a href="https://doi.org/10.1162/jocn.2010.21451">slowly then young adults</a>.</p>
<p>When it comes to brain structure, we typically see a decrease in the size of the brain in adults over age 65. This decrease is not just localized to one area. Differences can be seen across many regions of the brain. There is also typically an increase in cerebrospinal fluid that fills space due to the loss of brain tissue. In addition, white matter, the insulation on axons – long cables that carry electrical impulses between nerve cells – is also <a href="https://doi.org/10.1080/87565641003696775">less intact in older adults</a>. </p>
<p><a href="https://www.census.gov/library/publications/2014/demo/p25-1140.html">Life expectancy has increased</a> in the past decades. The goal is for all to live long and healthy lives, but even in the best-case scenario where one ages without disease or disability, older adulthood brings on changes in how we think and move. </p>
<p>Learning how all of these puzzle pieces fit together will help us unravel the mysteries of aging so that we can help improve quality of life and function for aging individuals. And now, in the context of COVID-19, it will help us understand the degree to which the brain may recover after illness as well. </p>
<p><em>This is an updated version of <a href="https://theconversation.com/preliminary-research-finds-that-even-mild-cases-of-covid-19-leave-a-mark-on-the-brain-but-its-not-yet-clear-how-long-it-lasts-166145">an article originally published</a> on Sept. 24, 2021.</em></p><img src="https://counter.theconversation.com/content/178499/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jessica Bernard receives funding from the National Institutes of Health. </span></em></p>New research offers insights into the brain after COVID-19 that may have implications for our understanding of long COVID-19 and how the disease affects our senses of taste and smell.Jessica Bernard, Associate Professor, Texas A&M UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1661452021-09-24T12:37:13Z2021-09-24T12:37:13ZPreliminary research finds that even mild cases of COVID-19 leave a mark on the brain – but it’s not yet clear how long it lasts<figure><img src="https://images.theconversation.com/files/422498/original/file-20210921-19-1kb6j0s.jpg?ixlib=rb-1.1.0&rect=0%2C25%2C5700%2C3763&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The new findings, although preliminary, are raising concerns about the potential long-term effects of COVID-19.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/coronavirus-covid-19-royalty-free-image/1220459949?adppopup=true">Yuichiro Chino via Getty Images</a></span></figcaption></figure><p>With more than <a href="https://theconversation.com/18-months-of-the-covid-19-pandemic-a-retrospective-in-7-charts-166881">18 months of the pandemic</a> in the rearview mirror, researchers have been steadily gathering new and important insights into the effects of COVID-19 on the body and brain. These findings are raising concerns about the long-term impacts that the coronavirus might have on biological processes such as aging. </p>
<p>As a <a href="https://scholar.google.com/citations?user=By7qto8AAAAJ&hl=en">cognitive neuroscientist</a>, <a href="https://liberalarts.tamu.edu/psychology/profile/jessica-bernard/">my past research</a> has focused on understanding how normal brain changes related to aging affect people’s ability to think and move – particularly in middle age and beyond. But as more evidence came in showing that COVID-19 could affect <a href="https://theconversation.com/deciphering-the-symptoms-of-long-covid-19-is-slow-and-painstaking-for-both-sufferers-and-their-physicians-164754">the body and brain</a> for months or longer following infection, my research team became interested in exploring how it might also impact the natural process of aging. </p>
<h2>Peering in at the brain’s response to COVID-19</h2>
<p>In August 2021, a <a href="https://doi.org/10.1101/2021.06.11.21258690">preliminary but large-scale study</a> investigating brain changes in people who had experienced COVID-19 drew a great deal of attention within the neuroscience community. </p>
<p>In that study, researchers relied on an existing database called the <a href="https://www.ukbiobank.ac.uk/">UK Biobank</a>, which contains brain imaging data from over 45,000 people in the <a href="https://doi.org/10.1038/s41467-020-15948-9">U.K. going back to 2014</a>. This means – crucially – that there was baseline data and brain imaging of all of those people from before the pandemic. </p>
<p>The research team analyzed the brain imaging data and then brought back those who had been diagnosed with COVID-19 for additional brain scans. They compared people who had experienced COVID-19 to participants who had not, carefully matching the groups based on age, sex, baseline test date and study location, as well as common risk factors for disease, such as health variables and socioeconomic status. </p>
<p>The team found marked differences in gray matter – which is made up of the cell bodies of neurons that process information in the brain – between those who had been infected with COVID-19 and those who had not. Specifically, the thickness of the gray matter tissue in brain regions known as the frontal and temporal lobes was reduced in the COVID-19 group, differing from the typical patterns seen in the group that hadn’t experienced COVID-19. </p>
<p>In the general population, it is normal to see some change in gray matter volume or thickness over time as people age, but the changes were larger than normal in those who had been infected with COVID-19.</p>
<p>Interestingly, when the researchers separated the individuals who had severe enough illness to require hospitalization, the results were the same as for those who had experienced milder COVID-19. That is, people who had been infected with COVID-19 showed a loss of brain volume even when the disease was not severe enough to require hospitalization.</p>
<p>Finally, researchers also investigated changes in performance on cognitive tasks and found that those who had contracted COVID-19 were slower in processing information, relative to those who had not. </p>
<p>While we have to be careful interpreting these findings as they await formal peer review, the large sample, pre- and post-illness data in the same people and careful matching with people who had not had COVID-19 have made this preliminary work particularly valuable.</p>
<h2>What do these changes in brain volume mean?</h2>
<p>Early on in the pandemic, one of the most common reports from those infected with COVID-19 was the loss of <a href="https://doi.org/10.1038/s41591-020-0916-2">sense of taste and smell</a>. </p>
<figure class="align-center ">
<img alt="A woman with COVID-19 symptoms tries to sense the smell of a fresh tangerine." src="https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/423005/original/file-20210923-14-2b3ens.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Some COVID-19 patients have experienced either the loss of, or a reduction in, their sense of smell.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/sick-woman-trying-to-sense-smell-of-fresh-tangerine-royalty-free-image/1298987743?adppopup=true">Dima Berlin via Getty Images</a></span>
</figcaption>
</figure>
<p>Strikingly, the brain regions that the U.K. researchers found to be impacted by COVID-19 are all linked to the olfactory bulb, a structure near the front of the brain that passes signals about smells from the nose to other brain regions. The olfactory bulb has connections to regions of the temporal lobe. We often talk about the temporal lobe in the context of aging and Alzheimer’s disease because it is where the <a href="https://doi.org/10.1073/pnas.1801093115">hippocampus</a> is located. The hippocampus is likely to play a key role in aging, given its involvement in memory and cognitive processes. </p>
<p>The sense of smell is also important to Alzheimer’s research, as some data has suggested that those at risk for the disease <a href="https://doi.org/10.1016/S0197-4580(01)00337-2">have a reduced sense of smell</a>. While it is far too early to draw any conclusions about the long-term impacts of these COVID-related changes, investigating possible connections between COVID-19-related brain changes and memory is of great interest – particularly given the regions implicated and their importance in memory and Alzheimer’s disease. </p>
<h2>Looking ahead</h2>
<p>These new findings bring about important yet unanswered questions: What do these brain changes following COVID-19 mean for the process and pace of aging? And, over time does the brain recover to some extent from viral infection?</p>
<p>These are active and open areas of research, some of which we are beginning to do in my own laboratory in conjunction with our ongoing work investigating brain aging. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Brain scans from a person in their 30s and a person in their 80s, showing reduced brain volume in the older adult brain" src="https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=576&fit=crop&dpr=1 600w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=576&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=576&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=724&fit=crop&dpr=1 754w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=724&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/418981/original/file-20210901-23-1110r23.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=724&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Brain images from a 35-year-old and an 85-year-old. Orange arrows show the thinner gray matter in the older individual. Green arrows point to areas where there is more space filled with cerebrospinal fluid (CSF) due to reduced brain volume. The purple circles highlight the brains’ ventricles, which are filled with CSF. In older adults, these fluid-filled areas are much larger.</span>
<span class="attribution"><span class="source">Jessica Bernard</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Our lab’s work demonstrates that as people age, the brain thinks and <a href="https://doi.org/10.1093/geronb/gbaa005">processes information differently</a>. In addition, we’ve observed changes over time in how <a href="https://doi.org/10.1016/j.neubiorev.2009.10.005">peoples’ bodies move</a> and how people learn new motor skills. Several <a href="https://doi.org/10.31887/DCNS.2001.3.3/dcpark">decades of work</a> have demonstrated that older adults have a harder time processing and manipulating information – such as updating a mental grocery list – but they typically maintain their knowledge of facts and vocabulary. With respect to motor skills, we know that <a href="https://doi.org/10.1016/j.neuropsychologia.2020.107620">older adults still learn</a>, but they do so more <a href="https://doi.org/10.1162/jocn.2010.21451">slowly then young adults</a>.</p>
<p>When it comes to brain structure, we typically see a decrease in the size of the brain in adults over age 65. This decrease is not just localized to one area. Differences can be seen across many regions of the brain. There is also typically an increase in cerebrospinal fluid that fills space due to the loss of brain tissue. In addition, white matter, the insulation on axons – long cables that carry electrical impulses between nerve cells – is also <a href="https://doi.org/10.1080/87565641003696775">less intact in older adults</a>. </p>
<p>As <a href="https://www.census.gov/library/publications/2014/demo/p25-1140.html">life expectancy has increased</a> in the past decades, more individuals are reaching older age. While the goal is for all to live long and healthy lives, even in the best-case scenario where one ages without disease or disability, older adulthood brings on changes in how we think and move.</p>
<p>Learning how all of these puzzle pieces fit together will help us unravel the mysteries of aging so that we can help improve quality of life and function for aging individuals. And now, in the context of COVID-19, it will help us understand the degree to which the brain may recover after illness as well. </p>
<p>[<em>Get the best of The Conversation, every weekend.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklybest">Sign up for our weekly newsletter</a>.]</p><img src="https://counter.theconversation.com/content/166145/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jessica Bernard receives funding from the National Institute on Aging and the National Institute of Mental Health. </span></em></p>Reduced brain volume in people who have experienced COVID-19 resembles brain changes typically seen in older adults. The implications of these findings are not yet clear.Jessica Bernard, Associate Professor, Texas A&M UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1235062019-12-09T13:43:33Z2019-12-09T13:43:33ZWhat makes wine dry? It’s easy to taste, but much harder to measure<figure><img src="https://images.theconversation.com/files/303844/original/file-20191126-112517-1ctucpx.jpg?ixlib=rb-1.1.0&rect=786%2C0%2C2781%2C1752&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A lot of of chemistry and physics are behind how you perceive a sip of wine.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/pouring-wine-647742124">GANNA MARTYSHEVA/Shutterstock.com</a></span></figcaption></figure><p>When you take a sip of wine at a family meal or celebration, what do you notice?</p>
<p>First, you probably note the visual characteristics: the color is generally red, rosé or white. Next, you smell the aromatic compounds wafting up from your glass.</p>
<p>And then there’s the sensation in your mouth when you taste it. White wine and rosé are usually described as refreshing, because they have brisk acidity and little to moderate sweetness. Those <a href="https://www.winemag.com/2017/09/21/why-calling-a-wine-dry-or-sweet-can-be-simply-confusing/">low levels of sugar</a> may lead you to perceive these wines as “dry.”</p>
<p>People also describe wines as dry when alcohol levels are high, usually over about 13%, mostly because the ethanol leads to hot or burning sensations that <a href="https://doi.org/10.1021/acs.jafc.6b03767">cover up other sensations</a>, especially sweetness. People also perceive red wines as dry or astringent because they contain a class of molecules called polyphenols. </p>
<p><a href="https://www.scopus.com/authid/detail.uri?authorId=55360215200">As an enologist</a> – a wine scientist – I’m interested in how all the chemistry in a glass of wine adds up to this perception of dryness. People are good at evaluating a wine’s dryness with their senses. Can we eventually come up with a way to automatically assess this dryness or astringency without relying on human tasters?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/303845/original/file-20191126-112522-dmwsr6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/303845/original/file-20191126-112522-dmwsr6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/303845/original/file-20191126-112522-dmwsr6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/303845/original/file-20191126-112522-dmwsr6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/303845/original/file-20191126-112522-dmwsr6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/303845/original/file-20191126-112522-dmwsr6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/303845/original/file-20191126-112522-dmwsr6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/303845/original/file-20191126-112522-dmwsr6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Molecules in grapes give them their various properties.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/ripe-red-wine-grape-ready-harvest-705572797">barmalini/Shutterstock.com</a></span>
</figcaption>
</figure>
<h2>The chemistry at the vineyard</h2>
<p>Everything starts with the grapes. If you taste a mature grape skin or seed at harvest, it will seem dry or astringent to you, thanks to a number of chemical compounds it contains.</p>
<p>Large molecules called condensed <a href="https://www.wineaustralia.com/getmedia/df422991-82ed-4125-b0f7-8395a63d438f/201005-tannin-management-in-the-vineyard.pdf">tannins</a> are mostly responsible for the astringency perception. These compounds are made up of varying types and numbers of <a href="https://doi.org/10.1021/bk-2002-0825.ch015">smaller chemical units called flavanols</a>. Tannins are in the same family of molecules, the polyphenols, that give grapes their red or black color. They tend to be larger in grape skins than in grape seeds, and consequently the skins tend to be more astringent, while the seeds are more bitter.</p>
<p><a href="https://doi.org/10.1021/bk-2002-0825.ch015">Grape varieties differ in how much</a> of each of these compounds they contain. In <em>Vitis vinifera</em> cultivars, like Pinot noir and Cabernet sauvignon, the tannin concentration varies from a relatively high 1 to 1.5 mg/berry. In cold-hardy hybrid grapes found in the Midwestern United States, <a href="https://doi.org/10.3390/fermentation3030047">like Frontenac and Marquette</a>, the concentrations are much lower, ranging from 0.3 to 0.7 mg/berry.</p>
<p><a href="https://www.wineaustralia.com/getmedia/df422991-82ed-4125-b0f7-8395a63d438f/201005-tannin-management-in-the-vineyard.pdf">Factors in the vineyard</a> – including site, soil qualities and amount of sun – affect the final concentration of tannins in the fruit.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/303614/original/file-20191126-84262-htad7o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/303614/original/file-20191126-84262-htad7o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/303614/original/file-20191126-84262-htad7o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/303614/original/file-20191126-84262-htad7o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/303614/original/file-20191126-84262-htad7o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/303614/original/file-20191126-84262-htad7o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/303614/original/file-20191126-84262-htad7o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/303614/original/file-20191126-84262-htad7o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Extracting tannins from red wines in the lab to characterize their chemical structure.</span>
<span class="attribution"><span class="source">Aude Watrelot</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>The chemistry in your mouth</h2>
<p>Basically, the more tannin there is in a wine, the more astringent it will be.</p>
<p>When you take a sip, the large tannin molecules <a href="https://doi.org/10.1016/j.tifs.2014.08.001">interact with proteins from your saliva</a>. They combine and form complexes, reducing the number of salivary proteins available to help lubricate your mouth. It leaves your mouth with a dry sensation – like if a snail were to lose its mucus layer, it would dry out.</p>
<p>Because everyone has a different composition and concentration of saliva proteins, and because the flow rate of saliva as you bring wine into your mouth varies, your perceptions of an astringent or dry wine won’t be the same as those of your friends or family. The alcohol level, pH and <a href="https://doi.org/10.1016/j.aca.2011.12.042">aroma of the wine</a> also influence how intensely and for how long you perceive a red wine’s dryness.</p>
<p>Since wine dryness is a perception, the most appropriate tool to appraise it is sensory evaluation. It requires panelists trained on the wine aroma, taste and mouthfeel based on prepared standards and other wines.</p>
<p>But winemakers would love to have a quick, simple way to objectively measure astringency without relying on human tasters. That way, they could easily compare this year’s wine to last year’s, or to another wine that is not available to be tested.</p>
<h2>Can we scientifically evaluate dryness?</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/303846/original/file-20191126-112522-wmdoz4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/303846/original/file-20191126-112522-wmdoz4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/303846/original/file-20191126-112522-wmdoz4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=787&fit=crop&dpr=1 600w, https://images.theconversation.com/files/303846/original/file-20191126-112522-wmdoz4.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=787&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/303846/original/file-20191126-112522-wmdoz4.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=787&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/303846/original/file-20191126-112522-wmdoz4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=989&fit=crop&dpr=1 754w, https://images.theconversation.com/files/303846/original/file-20191126-112522-wmdoz4.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=989&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/303846/original/file-20191126-112522-wmdoz4.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=989&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Part of the apparatus the author and Tonya Kuhl used at UC Davis to measure the friction between two surfaces.</span>
<span class="attribution"><span class="source">Aude Watrelot</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The challenge for me and my colleagues was to <a href="https://doi.org/10.1021/acs.jafc.9b01480">see if we could match up</a> the quantified chemical <a href="https://doi.org/10.1016/j.foodres.2018.09.043">and physical properties</a> in a wine to the trained panelists’ perceptions.</p>
<p>First, we used analytical methods to figure out the different sizes of tannins present in particular wines, and their concentrations. We investigated how these tannins interacted and formed complexes with standard salivary proteins.</p>
<p>My collaborators and I also used a physical approach, relying on a piece of equipment with two surfaces that are able to mimic and measure the forces of friction that occur in a drinker’s mouth between the tongue and the palate as wine and saliva interact. The friction forces increase between drier surfaces and decrease between more lubricated surfaces.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/304111/original/file-20191127-112484-xas3ab.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/304111/original/file-20191127-112484-xas3ab.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/304111/original/file-20191127-112484-xas3ab.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=630&fit=crop&dpr=1 600w, https://images.theconversation.com/files/304111/original/file-20191127-112484-xas3ab.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=630&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/304111/original/file-20191127-112484-xas3ab.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=630&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/304111/original/file-20191127-112484-xas3ab.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=791&fit=crop&dpr=1 754w, https://images.theconversation.com/files/304111/original/file-20191127-112484-xas3ab.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=791&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/304111/original/file-20191127-112484-xas3ab.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=791&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Researchers at Iowa State University’s Sensory Evaluation Lab passing wines to trained volunteers so they can report how dry they found particular wines.</span>
<span class="attribution"><span class="source">Aude Watrelot</span></span>
</figcaption>
</figure>
<p>Then, we trained human panelists to evaluate the intensity of dryness in the same wines and in a wine containing no tannins. </p>
<p>People perceived the wine containing the higher concentration of larger tannins as drier for a longer time than the wine without tannins. That made sense based on what we already knew about these compounds and how people sense them.</p>
<p>We were surprised, though, by our physical measurements in the lab, because they provided the opposite result as our human tasters’ perception. In the presence of too large or too many tannins in the wine, we recorded lower friction forces than in wines low in tannins. Based on the mechanical surfaces test, it seemed like there would be less dry mouthfeel than we’d expect in high-tannin wines. </p>
<p>My colleagues and I are planning to investigate this unexpected result in future research to improve our understanding of the dryness perception.</p>
<p>All its chemical and physical variables are part of what makes drinking wine a richly personal and ever-changing experience. Considering the impact of astringency on how individuals perceive a particular wine, a quick measure could be very helpful to winemakers as they do their work. So far, we haven’t been able to create a simple scale that will tell a winemaker that tannins at one certain level match up with a very particular dryness perception. But we enologists are still trying.</p>
<p>[ <em>You’re smart and curious about the world. So are The Conversation’s authors and editors.</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=youresmart">You can read us daily by subscribing to our newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/123506/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aude Watrelot has previously received funding from the American Vineyard Foundation.</span></em></p>Researchers would like to find a way to relate the human perception of dryness to the chemical and physical properties of the wine.Aude Watrelot, Assistant Professor of Enology, Iowa State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1125692019-04-11T12:31:54Z2019-04-11T12:31:54ZHow our sense of taste changes as we age<figure><img src="https://images.theconversation.com/files/264872/original/file-20190320-93028-1izo3se.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Favourite treats might not taste the same as they once did as we age.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/senior-woman-eating-icecream-1107354410">Rawpixel.com/Shutterstock</a></span></figcaption></figure><p>Taste is a complex phenomenon. We do not experience the sensation through a single sense (as we would when we see something using our sense of sight, for example) but rather it is made up of the five senses working together to allow us to appreciate and enjoy food and drink. Initial visual inspection of food indicates if we would consider consuming it. Then, when eating, smell and flavour combine to allow us to perceive a taste. Meanwhile, the mix of ingredients, texture and temperature can further impact how we experience it. </p>
<p>Unfortunately, this means that losing any of our senses, particularly smell or taste, can reduce our enjoyment of food. Think of the last time you had a cold or a blocked nose. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2579627/">It’s likely that</a> the temporary loss of smell changed the way you tasted food, lowered your appetite, or might even have caused you to overconsume as a means of seeking satisfaction and satiation. </p>
<p>A similar phenomenon <a href="https://academic.oup.com/jn/article/130/4/927S/4686631">happens when we get older</a>. The way we perceive taste starts to change by the age of 60 – when the sensitivity of our sense of smell <a href="https://www.sciencedaily.com/releases/2018/12/181219115505.htm">also starts to diminish</a> – becoming severe from the age of 70. </p>
<h2>Contributing senses</h2>
<p>As set out above, when our sense of smell functions less and is not able to detect and discriminate between different smells, it <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2579627/">affects our taste perception</a>. The decline in sensitivity of sense of smell with age is due to several factors, including a reduction in the number of olfactory receptors – which recognise different odour molecules – in the back of the nasal cavity, as well as a declining rate of regeneration of the receptor cells. </p>
<p>Another reason for impairment of the sense of taste with ageing is due to structural changes in the taste papillae. These bumpy structures host taste buds in the mouth, on the tongue and palate. One type of these papillae, fungiform, which contain high levels of taste buds, decreases in number as we age and <a href="https://www.ncbi.nlm.nih.gov/pubmed/23013608">also changes in shape</a>, becoming more closed. The more open the papillae, the easier it is for chemicals in food to come into contact with the receptors to create taste. Closed papillae <a href="https://academic.oup.com/chemse/article/43/2/117/4718453">reduce the contact surface</a> between food compounds and receptors resulting in less perception of food tastes. </p>
<figure>
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</figure>
<h2>Changing tastes</h2>
<p>Poor chewing is another factor that contributes to low detection of tastes. Due to ageing or poor oral health, some people lose their teeth, with many resorting to dentures. But dentures, particularly if ill-fitting, can affect the quality of chewing and breaking down of food compounds. This can then reduce the dissolution of the food compounds in saliva and reduces the contact levels with the sensory receptors in the taste buds. In addition, saliva secretion <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2579627/">can also decline</a> as a result of ageing. This means that there is less fluid to carry food compounds to the taste receptors, and less liquid available to help food compounds to dissolve, so taste is more poorly received. </p>
<p>General health also plays an important role in our sense of taste at any age. Head injuries, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2980431/pdf/0561142.pdf">medicinal drugs</a>, respiratory infections, <a href="https://www.macmillan.org.uk/information-and-support/coping/side-effects-and-symptoms/eating-problems/changes-in-taste.html">cancer</a>, radiation, and environmental exposure such as <a href="https://www.sciencedaily.com/releases/2014/03/140325094810.htm">smoke</a> and particulates can all contribute to an impaired sense of taste and exposure to many of these factors increase as we get older.</p>
<p>Not everyone’s sense of taste declines in the same way, however. Changes are known to be diverse among different people and genders, and not everyone shows the same level of impairment as they age. Though some things are inevitable, there are things that we can all do to at least reduce loss of taste. Our preliminary research, for example, has indicated that keeping a healthy diet, an active lifestyle, and ensuring a low to moderate consumption of the five tastes – sweet, sour, salt, umami and bitter – could help to slow down the changes in papillae.</p><img src="https://counter.theconversation.com/content/112569/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>As we get older, the way we experience taste can change drastically – but it’s not all down to one sense.Anita Setarehnejad, Senior Lecturer in Food Science and Technology, Cardiff Metropolitan UniversityRuth Fairchild, Senior Lecturer in Nutrition, Cardiff Metropolitan UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/826812017-08-25T01:21:29Z2017-08-25T01:21:29ZCan you pass this smell test?<figure><img src="https://images.theconversation.com/files/183335/original/file-20170824-18715-mn7b09.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The smell of daffodils is a treat for most people, but some cannot experience the joy because they have lost their sense of smell. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/handsome-man-smelling-flowers-670487011?src=hFOsW29bjol477j6y-m5pQ-1-0">Mila Supinskaya Glashchenko/Shutterstock.com</a></span></figcaption></figure><p>Each of our senses gives us a unique view of our world. Our visual system detects parts of the electromagnetic spectrum, revealing movement, brightness and color, but also a smile or a tear. Our auditory system registers changes in pressure, but also allows us to hear the crash of ocean waves or the smoky contralto of Billie Holiday. To appreciate the flavor of food and drink, recognize the perfume of the first spring flowers or detect the danger of a gas leak, we rely upon our olfactory (smell) and gustatory (taste) systems.</p>
<p>Smell and taste are intimately linked to each other. They are collectively known as chemical senses because each system functions to detect chemicals in our external environment. Our brains also process aspects of smell and taste together, especially when it comes to perceiving the flavor of food. </p>
<p>The chemical senses play hugely important roles in the lives of all animals. For example, a recent pair of studies showed that social order breaks down dramatically in <a href="http://www.sciencedirect.com/science/article/pii/S0092867417307729">ants with a disrupted olfactory system</a>. These animals, which rely on odors to communicate with each other the way humans rely on language, could no longer perceive important social messages sent between individuals.</p>
<p>Anosmia, which is the complete loss of smell, and other smell or taste disorders can be life-changing for humans, too. Because your brain combines smell and taste to create a perception of flavor, impairments in either of these senses can make food seem bland or even unpalatable. And while we don’t rely on odors to communicate the way ants do, <a href="http://www.fifthsense.org.uk/the-impact-of-smell-and-taste-disorders/">those who can’t smell</a> their new baby, their partner or the freshly mown grass can feel isolated from others and from the world around them.</p>
<p>Unfortunately, there are no effective treatments for most patients with smell and taste disorders. Additionally, patients often find it nearly impossible to be properly diagnosed or to receive support that can help to improve their quality of life – critical needs that we are helping to address in the laboratory and the clinic at the University of Florida <a href="http://cst.ufl.edu/">Center for Smell and Taste</a>.</p>
<h2>Test your knowledge</h2>
<p>How well do you know your chemical senses? Answer these true-or-false questions below to find out more. </p>
<p><strong>Humans can track scent on the ground the way dogs do.</strong></p>
<p>True.</p>
<p>The human sense of smell is better than you were told.
In fact, it <a href="http://science.sciencemag.org/content/356/6338/eaam7263.long">rivals that of other animals</a>. Humans can even follow a <a href="http://www.nature.com/neuro/journal/v10/n1/full/nn1819.html">scent track on the ground</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/183336/original/file-20170824-18715-1srqfoi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/183336/original/file-20170824-18715-1srqfoi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183336/original/file-20170824-18715-1srqfoi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183336/original/file-20170824-18715-1srqfoi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183336/original/file-20170824-18715-1srqfoi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183336/original/file-20170824-18715-1srqfoi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183336/original/file-20170824-18715-1srqfoi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Dogs in a field chase a scent.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/dogs-chasing-scent-654210652?src=WvOHXtn3h07kXsLQu1aXeQ-1-2">CG3/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>However, dogs, rodents and many other mammals are attuned to parts of the chemical world of which we are unaware: They can detect specialized odors such as <a href="http://www.annualreviews.org/doi/full/10.1146/annurev.physiol.70.113006.100608?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed">pheromones</a> that may influence social interactions, mating behaviors or aggression responses. There is little evidence supporting a role for pheromones in humans, no matter what those internet ads might say!</p>
<p><strong>Some people smell odors that aren’t there.</strong></p>
<p>True.</p>
<p>People with <a href="https://en.wikipedia.org/wiki/Phantosmia">phantosmia</a> perceive an odor even when there is not one present. These smell phantoms (there are taste phantoms, too) can have many causes, including nasal infections, neurological damage accompanying surgery or conditions such as epilepsy. Phantosmia is but one type of smell and taste disorder, the most common of which are hyposmia, which is diminished ability to smell, and anosmia, which is the inability to detect smells.</p>
<p><strong>Sweet taste can be an illusion.</strong></p>
<p>True.</p>
<p>Artichokes contain chemicals that don’t taste sweet on their own, but leave behind sweetness when washed away by a <a href="http://science.sciencemag.org/content/178/4064/988.long">drink of water</a>. These chemicals act by locking the sweet taste receptor in your mouth into the “off” position; when the chemical is washed away, the receptors all snap to the “on” position simultaneously, evoking a <a href="https://www.nature.com/nature/journal/v441/n7091/full/nature04765.html">sweet “water taste”</a> even in the absence of sugar or other sweeteners. The sweet taste inhibitor lactisole – a compound added to jams and jellies to dampen the intense sweetness from high concentrations of sugar used as a preservative – can elicit a similar perception.</p>
<p><strong>Mosquitoes (and other insects) have noses.</strong></p>
<p>False (technically). </p>
<p>But they do have have antennae and other structures that function much like the human nose to detect odors. And they use their sense of smell to find you when they want a meal. The insect repellent DEET works in part by <a href="http://www.biorxiv.org/content/biorxiv/early/2016/06/22/060178.full.pdf">disrupting the mosquito’s sense of smell</a>.</p>
<p><strong>Sour can taste sweet.</strong></p>
<p>True.</p>
<p>An unusual protein called miraculin, found in the “miracle fruit” of the tropical plant <em>Synsepalum dulcificum</em>, doesn’t taste sweet on its own but becomes a potent <a href="http://www.pnas.org/content/108/40/16819.long">sweetener when exposed to acids</a>. Suck on a lemon after eating a miracle fruit, and it will taste like lemon candy.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/183337/original/file-20170824-18715-iwsdo3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/183337/original/file-20170824-18715-iwsdo3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183337/original/file-20170824-18715-iwsdo3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183337/original/file-20170824-18715-iwsdo3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183337/original/file-20170824-18715-iwsdo3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183337/original/file-20170824-18715-iwsdo3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183337/original/file-20170824-18715-iwsdo3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A lemon will taste like candy after you eat miracle fruit.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/lemon-peel-448491604?src=dml1aqPGgH5D9vXiAthCng-1-54">grey_and/Shutterstock.com</a></span>
</figcaption>
</figure>
<p><strong>Smell and taste aren’t the only chemical senses.</strong></p>
<p>True.</p>
<p>While you can tell the difference between basil and garlic by their smell, your sense of taste is largely indifferent to herbs and spices. Then how do you sense of cooling of the menthol in mint, the heat of capsaicin in a habanero, or the tingling of sanshools in Szechuan peppercorns? Compounds in many herbs and spices trick temperature, pain and vibration sensors associated with the trigeminal nerve in the mouth and nose to give you these sensations. This third chemical sense is known as <a href="http://pubs.acs.org/doi/abs/10.1021/cn100102c">chemesthesis</a>. </p>
<p><strong>Mirrors can change smells.</strong></p>
<p>False. </p>
<p>A mirror won’t alter a smell. But some mirror image molecules (known as stereoisomers – think of comparing your right and left hands) have very different smells. The best-known stereoisomers that evoke very different aromas are <a href="https://en.wikipedia.org/wiki/Carvone">D-carvone and L-carvone</a>, which smell like caraway and spearmint, respectively.</p>
<p>Few people may appreciate the biology and chemistry that allows us to experience our chemical world. But those of us who study the chemical senses hope that our research will lead to tastier and healthier food, reduce the spread of insect-borne disease, improve the lives of people with smell or taste disorders and create a better understanding of the importance of smell and taste.</p>
<p><em>This article was written before anosmia became a common symptom of COVID-19.</em></p><img src="https://counter.theconversation.com/content/82681/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Steven D Munger receives funding from the University of Florida and from the National Institute on Deafness and Other Communication Disorders. He currently serves as the Past President of the Association for Chemoreception Sciences.</span></em></p>Our senses of taste and smell are linked to one another in ways that experts are continuing to explore. See if you can answer some questions for which experts have discovered some surprising answers.Steven D. Munger, Professor of Pharmacology and Therapeutics, University of FloridaLicensed as Creative Commons – attribution, no derivatives.