Science can explain the emotion of disgust. Photo credit: Public Domain

What's Behind the Disgust Response?

<p>As social creatures, we have a tendency to form connections with people we feel are similar to ourselves. On the other hand, we can stigmatize and marginalize groups we do not identify with, stereotyping them as morally corrupt or disgusting. We wondered: What’s behind the disgust response? Is the emotional response that might make someone recoil from potato salad that’s been in the fridge too long scientifically related to the impulse to avoid a person on the sidewalk or negatively stereotype an entire group of people?</p>
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<p>Among neuroscientists, disgust is seen as a motivational system that evolved to help us avoid dangers such as pathogens or toxins. Seen this way, the human body’s visceral disgust response—which includes symptoms like nausea or a reduced appetite—makes a lot of sense. Through such a reflex, the human body attempts to rid itself of dangerous substances or materials, or prevent itself from coming into contact with them.</p><p>Why, then, do we have the capacity to become disgusted in situations that do not pose an immediate threat to our well-being? The visceral reaction we have to things we find repulsive, including negative responses to people or behaviors, is not innate, but learned.</p><p><a href="https://www.theguardian.com/science/2018/jun/05/yuck-why-theres-more-to-disgust-than-not-getting-sick">A recent study</a> headed by self-proclaimed “disgustologist” Val Curtis at the London School of Hygiene and Tropical Medicine found that there might be different categories of disgust, one of which is atypical appearance. It may be this aspect of disgust that drives repulsion from people we see as different from ourselves. According to social neuroscientist Susan Fiske, “Disgust toward social outcasts avoids perceived moral and infectious contamination.” We may implicitly believe that there is something dangerous about someone that looks different from ourselves.</p>
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<p>Psychologists at St. Andrews University <a href="https://www.scientificamerican.com/article/how-disgusting-are-other-people/">demonstrated</a> how disgust relates to social groups by asking students to smell sweaty t-shirts. Students were faster to sanitize their hands after smelling shirts with a rival university’s logo than they were after smelling one with their own university’s logo.</p><p>Simply by changing the identity of who was wearing the shirt, researchers saw a change in the students’ response. This result suggests that social groupings have something to do with a disgust response.</p><p>When we interact with others in social situations, or process social information, our brain’s medial prefrontal cortex (mPFC) is active. Social neuroscientists Susan Fiske and Lasana Harris found that the mPFC was <a href="https://www.ncbi.nlm.nih.gov/pubmed/17100784">less active</a> when Princeton undergraduates were asked to make judgments about marginalized groups such as the homeless or people with substance use disorders. Furthermore, this lowered mPFC activity was coupled with brain responses indicative of a disgust response.</p><p>In <a href="https://academic.oup.com/scan/article/2/1/45/2362822">a follow-up study</a>, Fiske and Harris asked students to consider these individuals’ food preferences. When students were asked to evaluate whether the people in various images liked vegetables or not, their mPFCs showed increased activity. This change in brain response upon thinking about a person’s individual characteristics suggests that we may be less likely to stigmatize a group of people if we put ourselves in their shoes.</p>
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<p>Fiske says that “people can overcome disgust by individuating the other, thinking about their mind, needs, and preferences.” When we consider others—no matter how different they seem from us —thinking of them as people with wants and needs is key to remaining unbiased, especially when determining the fate of an entire group.</p>

<p>Among neuroscientists, disgust is seen as a motivational system that evolved to help us avoid dangers such as pathogens or toxins.</p>

CRISPR-Cas9 is a tool that lets scientists cut and insert small pieces of DNA at precise areas along a DNA strand. | Image Credit: Ernesto del Aguila III, National Human Genome Research Institute, NIH

Scientists Condemn Researcher's Use of CRISPR to Produce HIV-Resistant Babies

<p><i>Editor’s Note: This article was</i> <a href="http://app.nationalproduction.wgbh.org/e/es.aspx?s=2531&amp;e=1140105&amp;elqTrackId=87bceb0e8d45455b8e6ff9d7c932edc8&amp;elq=a69e7e142d4e48dbb42b060ec9cd3bb6&amp;elqaid=5544&amp;elqat=1"><i>originally published</i></a><i> in an edition of NOVA’s email newsletter, NOVA Lens, and has now been repurposed for NOVA Next. Sign up for NOVA Lens</i> <a href="http://www.pbs.org/wgbh/nova/newsletters.html"><i>here</i></a> <i>(select “NOVA Newsletters”).</i></p><p>This week has been a wild ride for scientists studying genome editing technologies—and perhaps for the human race at large.</p><p>It began on Sunday, when a scientist named He Jiankui (who has been on leave from the Southern University of Science and Technology in Shenzhen, China since February) announced in <a href="https://www.youtube.com/watch?v=th0vnOmFltc">a short YouTube video</a> that he’d taken what nearly all scientists perceive to be a drastic, premature, and highly unethical step: He and his team of collaborators had <a href="https://www.technologyreview.com/s/612458/exclusive-chinese-scientists-are-creating-crispr-babies/">eliminated a gene called CCR5 in the DNA of human embryos</a>, transferred those twin embryos into their mother’s uterus, and allowed the mother to carry her pregnancy to term and produce two live births. The scientists used a powerful tool called <a href="https://www.pbs.org/wgbh/nova/article/crispr-gene-drives/">CRISPR-Cas9</a>, which is cheap and easy to use, to modify the embryos’ genomes with the express goal of creating human children resistant to HIV infection (watch two explainer videos about CRISPR <a href="https://www.pbs.org/wgbh/nova/video/how-does-crispr-work/">here</a> and <a href="https://www.pbs.org/wgbh/nova/video/what-is-crispr-gene-editing/">here</a>).</p>
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<p>If confirmed, this would not be the first time a scientist had edited a human embryo. In April 2015, Chinese scientists <a href="https://link.springer.com/article/10.1007/s13238-015-0153-5">altered a non-viable human embryo</a> using CRISPR-Cas9, and in February 2016, a major scientific institution in London <a href="https://www.pbs.org/wgbh/nova/article/u-k-scientists-given-the-go-ahead-to-edit-genomes-of-human-embryos/">received the green light</a> from the U.K. Human Fertilization and Embryology Authority (HFEA) to use it on healthy human embryos. But this is the first reported example of gene editing that has resulted in a live birth (and <a href="https://www.wired.com/story/he-jiankui-gene-editing-crispr-second-pregnancy/">another</a> is allegedly in progress).</p><p>The announcement, which came before any evidence of publication or peer-review, blasted through the scientific community and the public eye just two days before the start of the International Human Genome Editing Summit at the University of Hong Kong. At the summit on Wednesday, He gave <a href="https://drive.google.com/drive/folders/1T1zLTtHS2z_cgl29fN_7qJg7fLA4qlrd">a 20-minute talk</a> defending his achievement before <a href="https://www.statnews.com/2018/11/28/chinese-scientist-defends-creating-gene-edited-babies/">an audience of critical and outraged scientists</a>. While attitudes toward CRISPR embryo editing remain mixed, the general consensus amongst experts is that He’s actions present a tremendous ethical breach on a variety of levels—most notably because he used a modified, viable embryo to create a human being without the full engagement of independent scientists, ethicists, regulators, or institutional review boards.</p><p></p><div>
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<p></p><p>“The fact that a CRISPR-edited embryo was allowed to initiate a pregnancy that turned into two live births is ethically appalling,” said Harvard University’s David Liu, who was at the summit in Hong Kong this week. “It’s hard to believe that so many ethical missteps actually took place that enabled such an event to happen.”</p><p>CRISPR-Cas9 is a gene-editing tool derived from an ancient bacterial immune system, CRISPR. This system’s function in bacteria is to identify the DNA of invading viruses and send in a specific type of enzyme, like Cas9, to target and “cut” a piece of DNA. Researchers realized that Cas9 could easily be artificially manipulated to recognize almost any sequence of DNA and cut it out. After the DNA is cut, DNA bases (A, T, C, or G) can be added to or removed from the genome. Since each amino acid—or building block of a protein—originates from a sequence of three bases, adding or deleting a couple of bases can significantly affect the protein produced. In many cases, adding one or two bases to a gene will result in a nonfunctional protein.</p>
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<p>In the case of the twins, who were dubbed the pseudonyms “Lulu” and “Nana,” the <a href="https://twitter.com/GaetanBurgio/status/1067657557114679296">researchers targeted CCR5</a>, a gene that provides the blueprint for a cell surface protein involved in immune function. While the protein is normally involved in relaying information between cells, HIV can use it to dock onto cells and infect them with its own genetic material. A small subset of the human population has a mutated version of CCR5, called ∆32, which yields a shorter version of the protein. People with two copies of this mutation are resistant to certain strains of HIV. He and his researchers may have been attempting to imitate the effect of this mutation by disrupting CCR5 via CRISPR-Cas9.</p><p>Because CRISPR-Cas9 induces mutations in a way that researchers cannot directly control, He and his colleagues were not able to exactly replicate the ∆32 mutation on a genetic level. Rather, they disrupted the CCR5 gene to create what Liu called a “mixture of disrupted gene products,” or nonfunctional versions of CCR5 that have different genetic alterations.</p><p>Since the researchers have not released any information on the specifics of the DNA they targeted, Liu says, “it’s difficult to speculate exactly what those products are.”</p><p>“That fact raises an additional degree of concern that it’s possible that the disrupted form of the CCR5 they generated is a different thing than the CCR5 ∆32 variant that occurs naturally,” Liu said. The ∆32 mutation has been conserved across generations, and is not known to have any negative impact on health. On the other hand, CCR5 variants generated via CRISPR-Cas9 could potentially have a negative affect on human health.</p><p></p><div>
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<p></p><p>CRISPR-Cas9 technology can also introduce unwanted mutations in the form of off-target effects that occur when Cas9 cuts in another, unintended location. Researchers in the genome-editing field conduct off-target analyses to characterize and minimize off-target effects in their experiments, but procedures for these analyses are still being refined and agreed upon by the genome editing community. He and his group have not released the details of any such analysis, and it remains unclear whether they investigated off-target effects to the high standard required for human research.</p><p>Also concerning is the fact that He modified germ cells as opposed to somatic cells. The former are sexually reproductive cells (like embryonic cells) that pass any edits on to future generations; that is, if Lulu or Nana eventually procreate, the edits they received as embryos will carry on inside the genomes of their offspring. “The ethical issues raised by embryo editing are quite distinct from, and more complicated, more extensive than those required for considering somatic cell editing,” Liu said.</p><p>The Southern University of Science and Technology has condemned He’s work, as have many <a href="https://news.berkeley.edu/2018/11/26/doudna-responds-to-claim-of-first-crispr-edited-babies/">academic</a> and <a href="https://www.broadinstitute.org/news/crispr-pioneers-feng-zhang-and-david-liu-respond-report-embryo-editing-china">medical</a> institutions around the world. The Chinese government itself put a stop to the research <a href="https://www.statnews.com/2018/11/29/china-halts-genome-editing-research-crispr-babies/">on Thursday</a>.</p><p>“The fact that the researcher’s institution is distancing itself from the work is deeply troubling because we rely on all of those parties—independent scientists, ethicists, institutional review panels, and governing bodies—to ensure that the health and well-being of patients is protected,” Liu said. (There are other red flags, too—including the fact that participants were given a consent form that falsely stated that the project was an AIDS vaccine trial.)</p>
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<p>Dana Waring, education director and co-founder of pgEd, the Personal Genetics Education Project, echoed Liu’s focus on the infants themselves, as well as the need to explore alternative angles to problems like <a href="https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(18)30098-7/fulltext">HIV rates</a> and the stigma associated with disease.</p><p>“This is a tool that needs to be used judiciously,” Waring said. “The first question I asked myself was, ‘What else is happening around HIV treatment prevention?’” In China, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4794244/">HIV-phobia runs rampant</a> and He himself cited HIV stigma as his primary motivation in going forward with the experiment.</p><p>“It’s an enormous risk for these children,” she said, adding that she dislikes the trending hashtag #CRISPRbabies. “These are human lives that are going to need a lot of enormous care and attention.”</p><p>Care for human life and this project’s impact on future therapy development drive Liu’s and the rest of the scientific community’s worries. “If we really want to maximize the effectiveness and the efficiency with which we bring these new potential therapeutic strategies to patients, we have to progress in a thoughtful and well-coordinated manner,” Liu said. He’s neglect of the genome editing community’s research principles, Liu added, “risks delaying or denying these potentially transformative therapies to the many other people that urgently need them.”</p>

<p>If confirmed, this would be the first reported example of gene editing that has resulted in a live birth.</p>

Fenway Park at night | Photo credit: Cody Carlson / Wikimedia Commons (CC BY-SA 3.0)

Inside the Mind of a Red Sox Fan

<p>The Boston Red Sox just <a href="https://www.wsj.com/articles/boston-red-sox-win-the-world-series-1540783069">won the 2018 World Series</a>. That’s great news for <a href="https://www.mlb.com/redsox">Red Sox</a> fans and for Boston—but also for scientists who’ve been studying the effects of group identity on human cognition. </p><p>The emotional highs and lows of sports are ultimately driven by community. Fans feel like they are a part of their favorite teams, and share in their successes and failures. They also may revel in the losses of their teams’ rivals. As such, sports like baseball provide a good starting point for researchers to investigate the <a href="https://qz.com/1451287/researchers-created-an-artificial-society-to-find-the-causes-of-religious-conflict/">us-against-them mentality</a> that characterizes so many of our social and political groups. </p><p>Using functional MRI (fMRI) to image the brain, Harvard psychologist <a href="https://psychology.fas.harvard.edu/people/mina-cikara">Mina Cikara</a>, along with her colleagues <a href="https://psychology.fas.harvard.edu/event/colloquium-matthew-m-botvinick-md-phd">Matthew Botvinick</a> and <a href="https://psych.princeton.edu/person/susan-fiske">Susan Fiske</a> at Princeton University, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3833634/">considered the brain activity </a>of 11 Red Sox and seven Yankees fans as they watched schematic baseball plays involving both teams. </p>
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<p>The scientists generated plays using screenshots from <a href="http://www.espn.com/">ESPN</a> to create animations, which showed the outcome of a single pitch. Each fan watched hypothetical scenarios in which their team succeeded against their rival, failed against their rival, and one in which their rival failed against a third team, <a href="https://www.mlb.com/orioles">the Orioles</a>. </p><p>When fans of either team watched their own team succeed, there was increased activity in the <a href="https://www.sciencedirect.com/topics/neuroscience/ventral-striatum">ventral striatum</a>, a region of the brain associated with learning and reward. They not only self-reported pleasure upon seeing their own team win, but also when their rival team did poorly, regardless of whether the rival lost to their own or a third team. </p><p>Cikara noted that “people who said they had that much more pleasure watching their rival fail were the same people who exhibited that much more activity in the ventral striatum.” In other words, the amount of pleasure people reported upon observing a baseball outcome correlated with a reward response in their brain. </p><p>In addition to reward, the ventral striatum is associated with reinforcement learning. Cikara wanted to know if the pleasure fans reported upon seeing their rival teams lose would reinforce negative behavior toward rival fans. “If watching your rival experiencing misfortune is constantly accompanied by the experience of pleasure, it’s possible that that pleasure is teaching you that you like these kinds of events.”  </p><p>Two weeks later, Cikara sent surveys to all the study’s participants asking how likely they would be to exhibit aggressive behaviors towards rival and Orioles fans. Comparing the results of these surveys to the brain activity she observed in fans, Cikara found that those who said they were more likely to harm rival fans also experienced higher activation of the ventral striatum upon seeing their rival team lose. </p><p>For Cikara, these results indicate how identifying with a particular group can affect our interpretation of certain events. "I’m not really a baseball fan at all, and so I watch these plays and I don’t feel anything. But for my Red Sox and my Yankees fans, they feel something very specific—they feel a pleasure response to their rival’s misfortunes.” But do feelings lead to actions? It remains unclear whether the reward response associated with seeing a rival lose directly impacts aggressive actions towards that rival. </p>
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<p>In a more recent <a href="http://www.psych.nyu.edu/vanbavel/lab/documents/Cikara.VanBavel.etal.2017.JEPG.pdf">study</a>, Cikara collaborated with New York University psychologist <a href="http://as.nyu.edu/psychology/people/faculty.jay-van-bavel.html">Jay Van Bavel</a> to look into how ingroups and outgroups are represented in the human brain. Via a coin toss, they divided participants into two teams: the Eagles and the Rattlers. The researchers then examined brain activity while participants read descriptions of people belonging to various groups. </p><p>Cikara and Van Bavel found similar patterns of brain activity when people read about fellow Eagles or Rattlers as when they read about fellow Democrats or Republicans. According to Van Bavel, this result may be indicative of <a href="https://www.facebook.com/NOVApbs/videos/1233374560163213/">how we think politically</a>. “Our tendency to divide the world up into us vs. them even over something arbitrary like a coin flip is also part of the way that we think about the political world around us. That we start to identify with a team even on a trivial basis, and that changes how we think about them.” </p><p>Identifying with a group can affect how we process information that contradicts our group identity. In a 2016 study, researchers at the University of Southern California used fMRI to look at the brain activity of participants as they considered opposing political opinions. Some of these participants exhibited higher activity in the <a href="https://www.sciencedaily.com/terms/amygdala.htm">amygdala</a>, a brain region associated with our fear response and other intense emotions like anger. Those with an increase in amygdala activity were also less likely to change their minds about the topic at hand, choosing instead to stay aligned with their group. </p><p>How we align ourselves with groups, whether they be a book club, a political party, or a baseball team, can affect our perceptions of people both alike and different from us by influencing our brain activity. The connections we make with others can change the connections in our brains.</p>
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<p>Researchers highlight the role of group formation in the success and survival of early humans. “Humans are pretty flimsy creatures, and throughout evolutionary history, we wouldn’t have survived on our own,” notes Van Bavel.</p><p>Though humans may have formed groups as a way to ensure protection from environmental threats, they also gained resources by working together. “We’re group organisms for a good reason. Our ancestors who were able to identify and cooperate with fellow group members reaped numerous benefits,” Cikara says. Our tendencies to flock to and collaborate with people similar to ourselves, then, are mostly likely vestiges of humankind’s beginnings. </p>

<p>Sports like baseball help researchers to investigate the <a href="https://qz.com/1451287/researchers-created-an-artificial-society-to-find-the-causes-of-religious-conflict/">us-against-them mentality</a> that characterizes many of our social and political groups. </p>

Nafisa Syed

Articles

What's Behind the Disgust Response?

Scientists Condemn Researcher's Use of CRISPR to Produce HIV-Resistant Babies

Inside the Mind of a Red Sox Fan

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