tag:theconversation.com,2011:/global/topics/meg-25370/articles
MEG – The Conversation
2021-03-10T19:06:28Z
tag:theconversation.com,2011:article/155475
2021-03-10T19:06:28Z
2021-03-10T19:06:28Z
Making a megalodon: the evolving science behind estimating the size of the largest ever killer shark
<figure><img src="https://images.theconversation.com/files/388736/original/file-20210310-13-17yzibt.jpg?ixlib=rb-1.1.0&rect=0%2C50%2C8365%2C5860&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Model based on a sculpture by Vlad Konstantinov/CDM Studios</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The giant prehistoric <em>Carcharocles megalodon</em> (or <em>Otodus megalodon</em> for some researchers) was the largest predatory shark to ever swim in Earth’s seas. Scientific evidence points to megalodon having lived between <a href="https://peerj.com/articles/6088/?fbclid=IwAR2zfYl7LxrXBWbY-RG4K7Z36-zjj6U0s3_AvlgHfHt785gTrqMZ7zJF1qA">16 million and 2.6 million years ago</a>, going extinct at the end of the <a href="https://www.britannica.com/science/Pliocene-Epoch">Pliocene Epoch</a> when the world’s oceans were much colder than today’s. </p>
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<img alt="" src="https://images.theconversation.com/files/387152/original/file-20210302-23-1ns3rqn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/387152/original/file-20210302-23-1ns3rqn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=216&fit=crop&dpr=1 600w, https://images.theconversation.com/files/387152/original/file-20210302-23-1ns3rqn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=216&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/387152/original/file-20210302-23-1ns3rqn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=216&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/387152/original/file-20210302-23-1ns3rqn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=271&fit=crop&dpr=1 754w, https://images.theconversation.com/files/387152/original/file-20210302-23-1ns3rqn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=271&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/387152/original/file-20210302-23-1ns3rqn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=271&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">Reconstruction of a 16m megalodon.</span>
<span class="attribution"><span class="source">Illustration by Oliver Demuth/Jack Cooper</span></span>
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<p>Over the years, <a href="https://www.tandfonline.com/doi/full/10.1080/08912963.2019.1666840">several</a> <a href="https://www.nature.com/articles/s41598-020-71387-y?fbclid=IwAR1VlijIgASwsZSgYLPZs4PuFZ-kHP6PkR5_0vf-u-IL_8Xm0sCwp2CgTNw%3Ca%20href=">research</a> papers have estimated meg’s size. Its teeth are shaped like large, flat triangles with serrated edges — much like the teeth of living <a href="https://www.nationalgeographic.com/animals/fish/facts/great-white-shark">white sharks</a>. White sharks, along with <a href="https://www.britannica.com/animal/mako-shark">mako sharks</a> and the <a href="https://oceana.org/marine-life/sharks-rays/porbeagle-shark">porbeagle shark</a> all belong in the family Lamnidae and are referred to as “lamnids”. </p>
<p>The close similarities between meg teeth and those of living lamnid sharks are strong evidence meg was indeed an ancient kind of lamnid shark. This premise is important, as it forms the basis of how we estimate the size of this ancient giant. </p>
<p>Two museum exhibits recently opened public displays featuring spectacular models of megalodon: one at the Smithsonian Museum of Natural History in Washington DC, and the other at the Western Australian Museum Boola Bardip in Perth. </p>
<p>These models, while both outstanding, don’t depict entirely the same shark. So how was each one made? And what scientific approaches were used? </p>
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Read more:
<a href="https://theconversation.com/giant-monster-megalodon-sharks-lurking-in-our-oceans-be-serious-53164">Giant monster Megalodon sharks lurking in our oceans: be serious!</a>
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<h2>Making the meghead</h2>
<p>The <a href="https://www.smithsonianmag.com/blogs/national-museum-of-natural-history/2019/07/29/megalodon-may-be-extinct-theres-life-size-one-smithsonian/">Smithsonian’s megalodon model</a> is a full-body reconstruction measuring 15 metres. The other, at the Museum Boola Bardip, is a beautifully crafted model of meg’s head. This was built under the direction of one of us (Mikael) and opened to the public in November.</p>
<p>The shape of the “meghead” is similar to a white shark’s head, but has a shorter and much rounder snout. Its colouration features “counter-shading” with a dark back and lighter belly — also similar to white sharks, but less contrasted. The greater this colour contrast, the easier it becomes for underwater predators to go unnoticed by prey.</p>
<p>The meghead’s jaw size was based on multiple teeth from a single ancient shark. These specimens allowed us to scale the body size to correspond with tooth size, as well as to match the widest front tooth of another megalodon found in Cape Range, Western Australia. </p>
<p>The rest of the meghead was then 3D modelled to fit the jaws. The end result was a head that corresponded to a creature roughly 14m in length. This would be the largest meg shark ever found in Western Australia, but not the largest overall.</p>
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<a href="https://images.theconversation.com/files/388750/original/file-20210310-23-1eahzyk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/388750/original/file-20210310-23-1eahzyk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/388750/original/file-20210310-23-1eahzyk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/388750/original/file-20210310-23-1eahzyk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/388750/original/file-20210310-23-1eahzyk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/388750/original/file-20210310-23-1eahzyk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=558&fit=crop&dpr=1 754w, https://images.theconversation.com/files/388750/original/file-20210310-23-1eahzyk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=558&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/388750/original/file-20210310-23-1eahzyk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=558&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">The giant megalodon head was scuplted by Vlad Konstantinov for Boola Bardip (WA Museum)</span>
<span class="attribution"><span class="source">Vlad Konstaninov, Mikael Siversson</span>, <span class="license">Author provided</span></span>
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<h2>Magnificent displays make for great selfies</h2>
<p>The Smithsonian meg model was overseen by Hans-Dieter Sues, a US paleontologist who drew the shark’s outline based on a general lamnid shark body plan. This was then finessed by University of Maryland shark fossil expert Bretton Kent.</p>
<p>After reviewing a small scale model, the full-size model was constructed based on a complete set of meg teeth assembled by Gordon Hubble, another megalodon expert. Measuring a whopping 15m, the final model had to be assembled as modules, as it wouldn’t have made it through the museum’s doors or corridors in one piece. </p>
<p>This model is now suspended by cables from the Smithsonian’s walls and ceiling, positioned strategically so visitors may take selfies from a nearby balcony.</p>
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<img alt="" src="https://images.theconversation.com/files/385495/original/file-20210222-15-qebldd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/385495/original/file-20210222-15-qebldd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/385495/original/file-20210222-15-qebldd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/385495/original/file-20210222-15-qebldd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/385495/original/file-20210222-15-qebldd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/385495/original/file-20210222-15-qebldd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/385495/original/file-20210222-15-qebldd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&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">The 15m-long megalodon model on display at the Smithsonian Museum of Natural History in Washington DC.</span>
<span class="attribution"><span class="source">Hans-Dieter Sues/Smithsonian Museum</span></span>
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<h2>Calculating maximum size</h2>
<p>The meghead model in Perth was based on several specific tooth specimens found locally and from overseas, painting a picture of a 14m-long predator. </p>
<p>However, to calculate the species’s <em>maximum</em> size, we first estimated the <a href="https://palaeo-electronica.org/content/2021/3284-estimating-lamniform-body-size?fbclid=IwAR15wOp4rV6j2VNyqxvdqYm4KTna4SdoU_82nBW7wOsywTAdiFcVnXq879g">maximum jaw size possible</a> for Meg and then scaled this up, using the same jaw size-to-body length ratio of living white sharks. </p>
<p>The maximum jaw size of meg can be calculated by scaling up the few known “associated dentitions” (multiple tooth specimens that were found together and came from a single shark) with the widest meg tooth ever found. </p>
<p>Once we did this, the size estimate we reached was between 19–20m. And this is much larger than most other recent estimates.</p>
<h2>The megashark lineage</h2>
<p>Scientists have discovered meg’s teeth to be part of a species continuum known as the <a href="https://www.popsci.com/story/science/megalodon-alive-myth/">megatooth shark lineage</a>. This is based on the discovery of many thousands of fossilised teeth that seem to merge into new shapes over time, pointing to the evolution of new species.</p>
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<img alt="" src="https://images.theconversation.com/files/388470/original/file-20210309-17-i15mi4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/388470/original/file-20210309-17-i15mi4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/388470/original/file-20210309-17-i15mi4.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/388470/original/file-20210309-17-i15mi4.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/388470/original/file-20210309-17-i15mi4.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/388470/original/file-20210309-17-i15mi4.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/388470/original/file-20210309-17-i15mi4.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">A newly discovered megalodon tooth from near Exmouth, Western Australia. The serrated edge shown here is 145mm long.</span>
<span class="attribution"><span class="source">Geoff Deacon/WA Museum</span></span>
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<p>The start of this lineage began in the Danian stage about 63 million years ago, when the first sharks of the genus <em>Otodus</em> appeared. This is why megalodon, belonging to this lineage, is now officially classified as <em>Otodus megalodon</em>. That said, the shark has been placed in various genera, including <em>Carcharocles</em> and <em>Procarcharodon</em>, and continues to be the <a href="https://www.gbif.org/species/144096597">subject of debate</a>.</p>
<p>With an estimated body length of about 4m, the first <em>Otodus</em> sharks in the megatooth lineage would have been smaller than several other sharks living at the time. So how could they have evolved to become the colossus that is meg?</p>
<p>DePaul University professor Kenshu Shimada has <a href="https://www.eurekalert.org/pub_releases/2021-01/tfg-mgb010421.php">suggested</a> meg’s huge size may have had something to do with a strange trait of lamnid sharks, which is that their young eat each other in the womb. </p>
<p>This behaviour, called “intrauterine cannibalism”, provides a ready source of nutrition for growing fetuses and <a href="https://www.tandfonline.com/doi/pdf/10.1080/08912963.2020.1812598">may have driven increased</a> growth in megalodon. That said, it would have also forced mothers to feed more actively, due to increased nutrition demand from the rapidly growing young. </p>
<p>This wouldn’t have helped meg’s survival when global temperatures cooled down about three million years ago. The cold spell would have killed off much of meg’s food sources, eventually triggering its extinction. </p>
<p>In recent years, coastal limestone outcrops in Western Australia have yielded several new exciting megalodon teeth. We hope these will tell us more about the story of meg and its variations which swam through the seas of ancient Australia.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/giant-ancient-sharks-had-enormous-babies-that-ate-their-siblings-in-the-womb-152903">Giant ancient sharks had enormous babies that ate their siblings in the womb</a>
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<img src="https://counter.theconversation.com/content/155475/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Long receives funding from The Australian Research Council</span></em></p><p class="fine-print"><em><span>Mikael Siversson works for Western Australian Museum. He has received funding for a field trip to Cape Range by the Minderoo Foundation and the Foundation for the WA Museum.</span></em></p>
Two museum exhibits, one in the Smithsonian and one in Australia, have opened public displays featuring the spectacular meg. But while both models are mega impressive, they’re not the same. Why?
John Long, Strategic Professor in Palaeontology, Flinders University
Mikael Siversson, Head of Department, Earth & Planetary Sciences, Western Australian Museum
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/61723
2016-06-29T20:05:39Z
2016-06-29T20:05:39Z
Each part of the brain has its own rhythmic ‘fingerprint’
<figure><img src="https://images.theconversation.com/files/128537/original/image-20160628-7842-1cev8s1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/cat.mhtml?lang=en&language=en&ref_site=photo&search_source=search_form&version=llv1&anyorall=all&safesearch=1&use_local_boost=1&autocomplete_id=&searchterm=EEG&show_color_wheel=1&orient=&commercial_ok=&media_type=images&search_cat=&searchtermx=&photographer_name=&people_gender=&people_age=&people_ethnicity=&people_number=&color=&page=1&inline=173834126">Image Point Fr/Shutterstock.com</a></span></figcaption></figure><p>Since Hans Berger first recorded neural activity from the human scalp with an electroencephalograph (EEG), in 1924, neuroscientists have been trying to make sense of the electrical pulses emitted by our grey matter. Recent studies have focused on brain oscillations (commonly called brain waves) which are thought to be the mechanism by which different brain regions <a href="http://science.sciencemag.org/content/304/5679/1926">communicate with each other</a>. Our latest study has shed some light on these curious oscillations. <a href="http://journals.plos.org/plosbiology/article?id=info:doi/10.1371/journal.pbio.1002498">We have discovered</a> that each region of the brain has a uniquely identifiable pattern of oscillations – their own rhythmic fingerprint.</p>
<p>Berger was the first to notice that neural activity seems to fluctuate at a rate of 10 cycles per second. He called this rhythm the alpha-wave. Since then, the methods to identify rhythmic activity have improved considerably, from counting how often a wave fluctuates within a second, to elaborate mathematical procedures, called spectral analyses. </p>
<p>Alpha is still the most obvious oscillation, but other types of oscillations (faster and slower ones) have been discovered. Neuroscientists have already found out a lot about specific functions of these rhythms, but it is difficult to get a clear picture of oscillations as they seem to be distributed more or less randomly across the brain. </p>
<p>In our study, we looked for patterns in the occurrence of oscillations that would help us to get a more organised view of rhythmic brain activity. We recruited 22 volunteers to participate in the experiment. Their instruction was to rest for a few minutes, with open eyes, while their neural activity was recorded. </p>
<p>We used a magnetoencephalograph (MEG, the magnetic equivalent of EEG) to measure magnetic fields produced by neural activity. From the recording of the magnetic fields it is possible to infer where in the brain the activity came from. This spontaneous brain activity can then be analysed in terms of the rhythms that occur there. By observing these oscillations over several minutes, we found that each brain area has its own characteristic mix of different rhythms over time. </p>
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<img alt="" src="https://images.theconversation.com/files/128666/original/image-20160629-15292-16bm8a3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128666/original/image-20160629-15292-16bm8a3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128666/original/image-20160629-15292-16bm8a3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128666/original/image-20160629-15292-16bm8a3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128666/original/image-20160629-15292-16bm8a3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128666/original/image-20160629-15292-16bm8a3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128666/original/image-20160629-15292-16bm8a3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&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">Unravelling the mysteries of the brain.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/cat.mhtml?lang=en&language=en&ref_site=photo&search_source=search_form&version=llv1&anyorall=all&safesearch=1&use_local_boost=1&autocomplete_id=&search_tracking_id=g6N70IxCYQOJjyLd7KffZg&searchterm=brain%20anatomy&show_color_wheel=1&orient=&commercial_ok=&media_type=images&search_cat=&searchtermx=&photographer_name=&people_gender=&people_age=&people_ethnicity=&people_number=&color=&page=1&inline=266669666">Jesada Sabai/Shutterstock.com</a></span>
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<p>In some regions, for example the visual cortex, there would only be two relatively slow rhythms (cycling at about ten times per second – the <a href="http://www.jneurosci.org/content/30/25/8692">alpha rhythm</a>. But in other regions, for example in the middle of the brain that is involved in things such as movement, learning and reward, there would be up to nine rhythms at many different time scales. These different oscillations could reflect how a particular region communicates with other regions in the brain. This means that regions with many different rhythms might have more complex tasks that involve communication with many other parts of the brain. </p>
<p>Although people can be quite different from each other in terms of their brain anatomy, we found that these rhythmic fingerprints were very similar across our healthy volunteers. In fact, they were so similar that we could take new data from other participants and label their brain areas based only on their oscillations, without knowing where the oscillations came from. </p>
<h2>Potential diagnostic tool</h2>
<p>Now that we know what pattern of oscillations to expect in each part of the brain in young, healthy adults, it should be possible to find differences in patients with illnesses that are expressed in these oscillations. As patients only have to rest and are not required to perform any tasks, using this as a tool would be possible even with severely impaired people. </p>
<p>Through the detailed analysis of oscillations in each brain part, it is possible to find small abnormalities that are only apparent in one particular rhythm in one brain region. One potential application of this could be to identify abnormal oscillations in a specific brain area in a patient and then use <a href="http://www.sciencedirect.com/science/article/pii/S0960982212007373">electric or magnetic brain stimulation</a> to modulate only these specific oscillations. </p>
<p>These kinds of noninvasive brain stimulation methods have already been proved successful in a few studies. For example, in patients with post-traumatic stress disorder, stimulating the frontal part of the brain with magnetic pulses has been shown to <a href="http://www.psychiatrist.com/JCP/article/Pages/2010/v71n08/v71n0805.aspx">reduce their symptoms</a>, improve mood and reduce anxiety. Knowing exactly how and where to stimulate brain oscillations in patients would be a big step towards improving these conditions.</p><img src="https://counter.theconversation.com/content/61723/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joachim Gross receives funding from Wellcome Trust, MRC and BBSRC. </span></em></p><p class="fine-print"><em><span>Anne Keitel 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>
It may prove to be a useful diagnostic tool for brain disorders.
Anne Keitel, University of Glasgow
Joachim Gross, Professor in Psychology, University of Glasgow
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/58970
2016-05-06T11:33:57Z
2016-05-06T11:33:57Z
In loud rooms our brains ‘hear’ in a different way – new findings
<figure><img src="https://images.theconversation.com/files/121417/original/image-20160505-19851-1mpv95s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">'Receiving you loud and clear.'</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/s/party+conversation/search.html?page=2&thumb_size=mosaic&inline=244297636">wavebreakmedia</a></span></figcaption></figure><p>When we talk face-to-face, we exchange many more signals than just words. We communicate using our body posture, facial expressions and head and eye movements; but also through the rhythms that are produced when someone is speaking. A good example is the rate at which we produce syllables in continuous speech – about <a href="http://www.nature.com/neuro/journal/v15/n4/full/nn.3063.html">three to seven times a second</a>. In a conversation, a listener <a href="http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001752">tunes in</a> to this rhythm and uses it to predict the timing of the syllables that the speaker will use next. This makes it easier for them to follow what is being said. </p>
<p>Many other things are also going on. Using <a href="http://ilabs.washington.edu/what-magnetoencephalography-meg">brain-imaging techniques</a> we know for instance that even when no one is talking, the part of our brain responsible for hearing <a href="http://www.nature.com/neuro/journal/v15/n4/full/nn.3063.html">produces</a> rhythmic activity at a similar rate to the syllables in speech. When we listen to someone talking, these <a href="http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001752">brain rhythms align</a> to the syllable structure. As a result, the brain rhythms match and track in frequency and time the incoming acoustic speech signal. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/121539/original/image-20160506-32044-1p5ql1x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/121539/original/image-20160506-32044-1p5ql1x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/121539/original/image-20160506-32044-1p5ql1x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=428&fit=crop&dpr=1 600w, https://images.theconversation.com/files/121539/original/image-20160506-32044-1p5ql1x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=428&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/121539/original/image-20160506-32044-1p5ql1x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=428&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/121539/original/image-20160506-32044-1p5ql1x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=538&fit=crop&dpr=1 754w, https://images.theconversation.com/files/121539/original/image-20160506-32044-1p5ql1x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=538&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/121539/original/image-20160506-32044-1p5ql1x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=538&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">Hit that perfect beat.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/cat.mhtml?lang=en&language=en&ref_site=photo&search_source=search_form&version=llv1&anyorall=all&safesearch=1&use_local_boost=1&autocomplete_id=&searchterm=brain%20waves&show_color_wheel=1&orient=&commercial_ok=&media_type=images&search_cat=&searchtermx=&photographer_name=&people_gender=&people_age=&people_ethnicity=&people_number=&color=&page=1&inline=186644801">DesignPrax</a></span>
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<p>When someone speaks, we know their lip movements help the listener, too. Often these movements precede the speech – opening your mouth, for example – and provide important cues about what the person will say. Yet even on their own, lip movements contain enough information to allow trained observers to understand speech without hearing any words – hence some people can lip-read, of course. What has been unclear until now is how these movements are processed in the listener’s brain. </p>
<h2>Lip-synching</h2>
<p>This was the subject of our <a href="https://elifesciences.org/content/5/e14521v1/article-data">latest study</a>. We already <a href="http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1000436">knew that</a> it is not just a speaker’s vocal chords that produce a syllable rhythm, but also their lip movements. We wanted to see whether listeners’ brain waves align to speakers’ lip movements during continuous speech in a comparable way to how they align to the acoustic speech itself – and whether this was important for understanding speech. </p>
<p>Our study has revealed for the first time that this is indeed the case. We recorded the brain activity of 44 healthy volunteers while they watched movies of someone telling a story. Just like the auditory part of the brain, we found that the visual part also produces rhythms. These align themselves to the syllable rhythm that is produced by the speaker’s lips during continuous speech. And when we made the listening conditions more difficult by adding distracting speech, which meant that the storyteller’s lip movements become more important to understand what they were saying, the alignment between the two rhythms became more precise. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/121540/original/image-20160506-32047-10ucrsc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/121540/original/image-20160506-32047-10ucrsc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/121540/original/image-20160506-32047-10ucrsc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/121540/original/image-20160506-32047-10ucrsc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/121540/original/image-20160506-32047-10ucrsc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/121540/original/image-20160506-32047-10ucrsc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=397&fit=crop&dpr=1 754w, https://images.theconversation.com/files/121540/original/image-20160506-32047-10ucrsc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=397&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/121540/original/image-20160506-32047-10ucrsc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=397&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Helpful lips.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/cat.mhtml?lang=en&language=en&ref_site=photo&search_source=search_form&version=llv1&anyorall=all&safesearch=1&use_local_boost=1&autocomplete_id=&search_tracking_id=rgyxGMJQKeUeABlIVzSAgw&searchterm=two%20people%20talking&show_color_wheel=1&orient=&commercial_ok=&media_type=images&search_cat=&searchtermx=&photographer_name=&people_gender=&people_age=&people_ethnicity=&people_number=&color=&page=1&inline=232893838">Rocketclips, Inc</a></span>
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<p>In addition, we found that the parts of the listener’s brain that control lip movements also produce brain waves that are aligned to the lip movements of the speaker. And when these waves are better aligned to the waves from the motor part of the speaker’s brain, the listener understands the speech better. This supports the <a href="http://www.cell.com/current-biology/abstract/S0960-9822(15)00500-X?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS096098221500500X%3Fshowall%3Dtrue">idea that</a> brain areas that are used for producing speech are also important for understanding speech, and could have implications for studying lip-reading between people with hearing difficulties. Having shown this in relation to a speaker and listener, the next step will be to look at whether the same thing happens with brain rhythms during a two-way conversation.</p>
<p>Why are these insights interesting? If it is correct that speech normally works by establishing a channel for communication through aligning brain rhythms to speech rhythms – similar to tuning a radio to a certain frequency to listen to a certain station – our results suggest that there are other complementary channels that can take over when necessary. Not only can we tune ourselves to the rhythms from someone’s vocal chords, we can tune into the equivalent rhythms from their lip movement. Instead of doing this with the auditory part of our brain, we do it through the parts associated with seeing and movement. </p>
<p>And neither do you need to be a trained lip-reader to benefit – this is why even in a noisy environment such as a pub or a party, most people can still communicate with each other.</p><img src="https://counter.theconversation.com/content/58970/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joachim Gross has received funding in the past from the Wellcome Trust, BBSRC, ESRC, MRC and Volkswagen Stiftung.</span></em></p><p class="fine-print"><em><span>Hyojin Park 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>
Our heads are like radio receivers, and they can tune in to various different channels.
Joachim Gross, Professor in Psychology, University of Glasgow
Hyojin Park, Research Associate, University of Glasgow
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/54035
2016-03-30T19:10:16Z
2016-03-30T19:10:16Z
Is anyone there? About consciousness and its disorders
<figure><img src="https://images.theconversation.com/files/113351/original/image-20160301-8060-e9tdvk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Consciousness remains one of the most puzzling phenomena in science.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/lunettas/4446279433/in/photolist-7LUkYe-pCS45B-qsKrC9-6xd5i1-3gRe7U-4Fgqht-3dwbYC-A9XgD-4FkDaf-dUMc7o-3gRdnU-2DqnMP-r6Yqr8-r3PPTB-5QLnBD-6MAkqr-663hca-rdC2SU-qP5c6M-rtNwnR-7owVC8-6qVTFR-8cC6xb-4FkDuA-7VJwKV-nU8cYW-4FgqeP-bQusFe-bdHt5a-bBzLSy-4FkDdu-5wBq4R-61kJH1-4FkDyN-fSnPUg-6jRwfm-rP5Lgy-7vBfdL-569uxh-6dN1rk-FqhpG-qX8Gab-5ZQsh9-qrFdT9-WftJ6-bz8zVs-4FkDKf-ezAUdq-4FkDbw-wuycKz">Melissa Portes/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Imagine you just woke up from a deep, dreamless sleep. Fuzzy at first, you suddenly become aware of your surrounding, your body, your reality. </p>
<p>We say at this point that you are conscious. But although familiar and intimate to all of us, <a href="https://theconversation.com/uk/topics/consciousness">consciousness remains one of the most puzzling</a> phenomena in science. </p>
<p>How does the electric and chemical activity in your brain produce your subjective experiences; the redness of red, the taste of chocolate or the pain in your back? </p>
<p>So far, science hasn’t provided a plausible explanation of how these subjective qualities (called <a href="https://theconversation.com/learning-experience-lets-take-consciousness-in-from-the-cold-6739">qualia</a>) are produced by the brain. </p>
<p>Instead of directly tackling this <a href="http://consc.net/papers/facing.html">“hard problem” of consciousness</a>, neuroscience has focused on identifying the neural correlates of consciousness (<a href="http://consc.net/papers/ncc2.html">NCC</a>). These are the neural events <em>associated with</em> conscious experience.</p>
<h2>Neural correlates of consciousness</h2>
<p>Like waves, brain activity oscillates. These oscillations can be measured by neuro-imaging techniques such as <a href="http://www.hopkinsmedicine.org/healthlibrary/test_procedures/neurological/electroencephalogram_eeg_92,P07655/">EEG</a> (where electrodes pasted on the scalp detect electrical charges of brain cell activity), <a href="http://ilabs.washington.edu/what-magnetoencephalography-meg">MEG</a> (a technique that maps brain activity by recording the magnetic fields of electric currents) and <a href="http://www.ndcn.ox.ac.uk/divisions/fmrib/what-is-fmri">fMRI</a> (that measures brain activity by detecting changes associated with blood flow), across time scales that range from milliseconds to seconds. </p>
<p>Early studies measuring electrical activity of the brain with EEG in sleep and awake states found that fluctuations in the awake conscious state are small and fast (<a href="http://science.sciencemag.org/content/124/3231/1066">alpha oscillations</a> between 8 and 12 Hz) in comparison to the big, slow <a href="http://science.sciencemag.org/content/124/3231/1066">delta oscillations</a> (between 0.25 and 4 Hz) in deep sleep, when subjects lose consciousness. </p>
<p>But the change of these oscillations (from fast alpha to slow delta waves) may not reflect the whole picture of what is happening in your brain when you lose or regain consciousness.</p>
<p>fMRI studies in the resting awake state have revealed that the low-frequency fluctuations (<0.1Hz) between distant parts of the brain are actually <a href="http://www.nature.com/news/neuroscience-idle-minds-1.11440">synchronised</a>, forming distinct patterns of correlation across the brain. The <a href="http://online.liebertpub.com/doi/abs/10.1089/brain.2011.0049">shape of these correlation patterns</a> actually changes when we lose consciousness. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/114753/original/image-20160310-26261-iiafzw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/114753/original/image-20160310-26261-iiafzw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/114753/original/image-20160310-26261-iiafzw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=306&fit=crop&dpr=1 600w, https://images.theconversation.com/files/114753/original/image-20160310-26261-iiafzw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=306&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/114753/original/image-20160310-26261-iiafzw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=306&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/114753/original/image-20160310-26261-iiafzw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=385&fit=crop&dpr=1 754w, https://images.theconversation.com/files/114753/original/image-20160310-26261-iiafzw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=385&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/114753/original/image-20160310-26261-iiafzw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=385&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Spatially distant parts of the brain show synchronised activity (shown as similar colours) and form very distinct patterns of correlation across the brain.</span>
<span class="attribution"><a class="source" href="http://www.pnas.org/content/102/27/9673.abstract">M.Fox et al, The human brain is intrinsically organized into dynamic, anticorrelated functional networks, PNAS vol. 102 no. 27/Copyright © 2005, The National Academy of Sciences</a></span>
</figcaption>
</figure>
<p>Imagine each of these patterns as a building block making up the changing brain activity patterns, just like musical notes make up a melody. When characterised in terms of these building blocks, the dynamics of the conscious brain are composed of a <a href="http://www.pnas.org/content/112/3/887.abstract">richer</a>, <a href="http://www.nature.com/ncomms/2016/160121/ncomms10340/full/ncomms10340.html">more flexible repertoire</a> of correlation patterns compared to the brain during sleep or under anaesthesia. </p>
<p>Studying brain dynamics during loss and recovery of consciousness through these correlation patterns can give us a better understanding of its neural correlates and reveal the signature of consciousness. But why do we even need to find this “signature”?</p>
<h2>Disorders of consciousness</h2>
<p>Besides genuine curiosity in understanding the brain’s inner workings and the nature of consciousness, there is an urgent clinical need to understand and accurately diagnose disorders of consciousness.</p>
<p>After several weeks in coma – a state where patients are unconscious and unable to be aroused to consciousness by stimuli – most either die or transition into what is called a <a href="https://en.wikipedia.org/wiki/Persistent_vegetative_state">vegetative state</a>. </p>
<p>Here they don’t show any behavioural signs, <a href="http://cirrie.buffalo.edu/encyclopedia/en/article/133/">not even opening their eyes</a>, and are thought to be unconscious. But recent findings show that a subgroup of patients previously diagnosed as being in vegetative state are actually <a href="http://www.neurology.org/content/58/3/349.short">minimally conscious</a>. </p>
<p>This means they show inconsistent but discernible, non-reflexive behaviours, such as sustained visual fixation or responses to a verbal order, although they are still unable to communicate. </p>
<p>Current diagnostic methods based on observing the patient’s behaviour have led to <a href="http://bmcneurol.biomedcentral.com/articles/10.1186/1471-2377-9-35">41% being misdiagnosed</a>. Such a misdiagnosis could cause the patient to suffer, create legal and ethical dilemmas or even end a conscious person’s life.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/116729/original/image-20160330-28459-5mba06.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/116729/original/image-20160330-28459-5mba06.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/116729/original/image-20160330-28459-5mba06.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/116729/original/image-20160330-28459-5mba06.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/116729/original/image-20160330-28459-5mba06.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/116729/original/image-20160330-28459-5mba06.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/116729/original/image-20160330-28459-5mba06.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">
<figcaption>
<span class="caption">Recent findings show that a subgroup of patients previously diagnosed as being in vegetative state are actually minimally conscious.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/msvg/5197694152/in/photolist-8Vixoq-qrUZJb-5i4EQh-f4k5a2-qFaVta-Fn1mL-6URQng-7Z1NL7-7RvAC-n8Rod3-KZ2So-bDAvNY-DD3Y4-py3Csc-aC5rMM-zK6P9-o5yVpm-9MW997-nHY1xi-dzGbtN-qhurSQ-5k9dYy-eaZHvx-7mnYAZ-4VY9XJ-5uQLJN-qSrSmi-j1bpof-7WA2Sg-99bXm-aE7vph-9VrCee-3BYENt-5psV2r-godLkJ-5HAZyb-8LjU57-9ZAwS1-dYVfQP-dRqzWN-aP21Mx-iJGmXD-q59YgA-7XZLt1-pEgYDW-gfcQgu-4dVGQC-85eFwf-4QXzv7-dqbZiJ">Michael Gil/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>A <a href="http://www.nature.com/news/neuroscience-the-mind-reader-1.10816">2006 study clearly demonstrated</a> a case of such misdiagnosis. The authors asked a 23 year old woman in a vegetative state to imagine playing tennis and walking through the rooms of her house while her brain activity was scanned using fMRI. Her activity showed similar patterns to that of healthy adults who imagine playing tennis or navigating through their houses. </p>
<p>Although this study pioneered the <a href="https://theconversation.com/scanning-brain-energy-could-help-predict-who-will-wake-from-vegetative-state-25675">use of functional imaging to diagnose disorders of consciousness</a>, it had one major limitation. It required a patient’s active (mental) participation and response to a command, such as “imagine playing tennis”.</p>
<p>But the absence of a response from the patient does not imply he is unconscious. He may simply be failing to perform the task while being conscious.</p>
<h2>Absence of evidence</h2>
<p>In an <a href="http://stm.sciencemag.org/content/5/198/198ra105.short">alternative method</a> of diagnosis, electromagnetic pulses are sent through the scalp while the complexity of the brain’s response to these pulses is evaluated with EEG. In the awake state, these pulses lead to more complex and longer lasting changes in brain activity compared to when consciousness is lost in sleep, anaesthesia or coma. </p>
<p>Although this method eliminates the need for a patient’s active participation, it requires a new and not always readily available setup of transcranial magnetic stimulation (<a href="https://theconversation.com/zapping-the-brain-with-tiny-magnetic-pulses-improves-memory-32524">TMS</a>) as well as a compatible EEG device. </p>
<p>So studying changes in resting state brain activity remains important in the search for signatures of consciousness without asking patients to perform tasks (such as imagining playing tennis) or stimulating the brain with external pulses (such as using TMS).</p>
<p>These tests are a major step in the developing <a href="https://theconversation.com/learning-experience-lets-take-consciousness-in-from-the-cold-6739">science of consciousness</a> and provide an important diagnostic tool. But we have to remember the absence of evidence is not evidence of absence.</p><img src="https://counter.theconversation.com/content/54035/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Selen Atasoy 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>
Consciousness is one of the most puzzling phenomena in science. How does the electric and chemical activity in your brain produce your subjective experiences; the colour red or the taste of chocolate?
Selen Atasoy, Postdoctoral Research Fellow, UNSW Sydney
Licensed as Creative Commons – attribution, no derivatives.