ORGAN REPAIRS DENGUE DEBACLE HOW EELS GET ELECTRIC The forgotten compound that can A vaccination program Insights into their shocking repair damaged tissue PAGE 56 gone wrong PAGE 38 attack mechanisms PAGE 62 MIND READER A new brain-machine interface detects what the user wants PLUS QUANTUM GR AVIT Y IN A LAB Could new experiments APRIL 2019 pull it off? PAGE 48 © 2019 Scientific American ScientificAmerican.com APRIL 2019 VOLUME 320, NUMBER 4 48 NEUROTECH PHYSICS 24 The Intention Machine 48 Quantum Gravity A new generation of brain-machine in the Lab interface can deduce what a person Novel experiments could test wants. By Richard Andersen the quantum nature of gravity on a tabletop. By Tim Folger INFRASTRUCTURE 32 Beyond Seawalls MEDICINE Fortified wetlands and oyster reefs 56 A Shot at Regeneration can protect shorelines better than A once forgotten drug compound hard structures. By Rowan Jacobsen could rebuild damaged organs. By Kevin Strange and Viravuth Yin PUBLIC HEALTH 38 The Dengue Debacle ANIMAL PHYSIOLOGY In April 2016 children in the Philip- 62 Shock and Awe pines began receiving the world’s Understanding the electric eel’s first dengue vaccine. Almost two unusual anatomical power. years later new research showed By Kenneth C. Catania ON THE COVER Tapping into the brain’s neural circuits lets people that the vaccine was risky for many MATHEMATICS with spinal cord injuries manipulate computer kids. The campaign ground to 70 Outsmarting cursors and robotic limbs. Early studies underline a halt, and the public exploded a Virus with Math the need for technical ad­­vances that make in outrage. What went wrong? How calculus helped to drive brain-machine interfaces faster and more versatile. The latest versions may begin to realize By Seema Yasmin and the fight against HIV. the promise of direct neural communication. Madhusree Mukerjee By Steven Strogatz Illustration by Mark Ross. Photograph by Mattia Balsamini April 2019, ScientificAmerican.com 1 © 2019 Scientific American 3 From the Editor 4 Letters 6 Science Agenda Has the World Health Organization taken a perilous step by endorsing traditional Chinese medicine? By the Editors 7 Forum Forests’ ability to sequester carbon could mitigate climate change. By Han de Groot 8 Advances Developing a “cochlear implant for smell.” Some forms of bias are declining. Identifying ancient predators. How to fail successfully. Finding the entropy in art. 10 20 The Science of Health Treatments of just hours or days can work for OCD, phobias and other conditions. By Claudia Wallis 22 Ventures Keep mind reading out of neural interfaces. By Wade Roush 76 Recommended Documentary and companion book about planet Earth. Realism and quantum mechanics. Saving a generation from the effects of thalidomide. By Andrea Gawrylewski 77 The Intersection YouTube’s recommendation algorithms lead users down rabbit holes. By Zeynep Tufekci 78 Anti Gravity 20 Arctic warming made January’s weather weird and wacky. By Steve Mirsky 79 50, 100 & 150 Years Ago 80 Graphic Science Introducing new words that last. By Mark Fischetti and Valentina D’Efilippo ON THE WEB A New Era of Human Spaceflight Rockets and spacecraft built by SpaceX and Boeing are set to transport U.S. astronauts to the International Space Station. Scientific Americandetails the rise of “New Space.” Go to www.ScientificAmerican.com/apr2019/new-space 76 Scientific American (ISSN 0036-8733), Volume 320, Number 4, April 2019, published monthly by Scientific American, a division of Springer Nature America, Inc., 1 New York Plaza, Suite 4600, New York, N.Y. 10004-1562. Periodicals postage paid at New York, N.Y., and at additional mailing offices. Canada Post International Publications Mail (Canadian Distribution) Sales Agreement No. 40012504. Canadian BN No. 127387652RT; TVQ1218059275 TQ0001. Publication Mail Agreement #40012504. 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Scientific American maintains a strict policy of editorial independence in reporting developments in science to our readers. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 2 Scientific American, April 2019 © 2019 Scientific American FROM Mariette DiChristina is editor in chief of Scientific American. THE EDITOR Follow her on Twitter @mdichristina The Joy of Science “I get goose bumps every time I see it.” “I saw something so What was so strange a biologist had to drop other things to strange that I had to drop everything else to investigate.” “A tale check it out? Kenneth C. Catania explains the allure of the of shark bites at a Scottish pub has led us to some new ideas electric eel’s shocking attacks. As an eel hit a prey fish in a tank about rebuilding broken bodies.” with high voltage, all the other nearby fish became Those sentences appear in three of stock-still in just three milliseconds, floating like the feature articles in this issue writ- “little statues” in the water. “I was hooked,” Catania ten by the researchers who are doing describes in “Shock and Awe,” his fourth article the work. As a culture, we often focus for Scien tific American. “I had to know how the on the achievements of science. But for eel’s electric attack worked.” In a series of me, the stories of how we got to those out- experiments, he has discovered how the comes—including the side tracks and the eel em ploys electric fields to track and bumps in the road—are not to be missed. immobilize prey. When threatened by And you can find them in our print and digi- a potential predator, it can leap tal editions. from the water to intensify the What gives a neuroscientist goose bumps, current delivered. You can learn for instance? In “The Intention Machine,” the how by turning to page 62. issue’s cover story, Richard Andersen writes Dive into “A Shot at Regenera- about watching a paralyzed person in a wheelchair tion,” beginning on page 56, to find using thoughts to control a computer or a robotic out how shark bites drew the attention of inves- limb. These brain-machine interfaces can send and tigators Kevin Strange and Viravuth Yin: not the bites them- receive communications to and from neural circuits selves, actually, but what happened to the wounded dolphins in the body. Whereas existing interfaces are imprecise or slug- afterward. Strange and Yin heard a story about how dolphins gish, newer versions could be placed in brain areas that would were beset by sharks, receiving bite wounds “45 centimeters allow them to deduce a person’s intentions to move. That would long and 12 centimeters deep. But remarkably the dolphins make them more versatile for individuals with certain injuries. healed up in weeks, with no signs of infection.” What could heal Andersen’s feature starts on page 24. tissue so quickly? I won’t spoil the surprise. BOARD OF ADVISERS Leslie C. Aiello Edward W. Felten Lene Vestergaard Hau Satyajit Mayor Daniela Rus President, Wenner-Gren Foundation Director, Center for Information Mallinckrodt Professor Senior Professor, National Center Andrew (1956) and Erna Viterbi Professor for Anthropological Research Technology Policy, Princeton University of Physics and of Applied Physics, for Biological Sciences, Tata Institute of Electrical Engineering and Computer Science and Director, CSAIL, M.I.T. Jonathan Foley Harvard University of Fundamental Research Robin E. Bell Eugenie C. Scott Executive Director and William R. Hopi E. Hoekstra John P. Moore Research Professor, Lamont-Doherty Chair, Advisory Council, and Gretchen B. Kimball Chair, Alexander Agassiz Professor Professor of Microbiology and Earth Observatory, Columbia University National Center for Science Education California Academy of Sciences of Zoology, Harvard University Immunology, Weill Medical Emery N. Brown College of Cornell University Terry Sejnowski Edward Hood Taplin Professor of Jennifer Francis Ayana Elizabeth Johnson Professor and Laboratory Medical Engineering and of Senior Scientist, Woods Hole Founder and CEO, Donna J. Nelson Head of Computational Computational Neuro science, M.I.T., Research Center Ocean Collective Professor of Chemistry, Neurobiology Laboratory, and Warren M. Zapol Professor Kaigham J. Gabriel Christof Koch University of Oklahoma Salk Institute for Biological Studies of Anesthesia, Harvard Medical School President and Chief Executive Officer, President and CSO, Robert E. Palazzo Meg Urry Charles Stark Draper Laboratory Allen Institute for Brain Science Dean, University of Alabama Vinton G. Cerf Israel Munson Professor of Physics at Birmingham College Chief Internet Evangelist, Google Harold “Skip” Garner Morten L. Kringelbach and Astronomy, Yale University Executive Director and Professor, Associate Professor and Senior of Arts and Sciences George M. Church Michael E. Webber Primary Care Research Network Research Fellow, The Queen’s College, Rosalind Picard Director, Center for Computational Co-director, Clean Energy Incubator, and Center for Bioinformatics University of Oxford Professor and Director, Affective Genetics, Harvard Medical School and Associate Professor, and Genetics, Edward Via College Robert S. Langer Computing, M.I.T. Media Lab Department of Mechanical Engineering, Rita Colwell of Osteopathic Medicine David H.