Brain-on-a-chip. Dazzling in green and magenta this image shows the nerve fibres (in green) produced by neural stem cells (in magenta) as they grow on a synthetic gel. Captured by a technique known as confocal microscopy, the image is part of research shedding light on how tinkering with the environment can affect the way in which nerve fibres grow. (Photo by Collin Edington and Iris Lee/Massachusetts Institute of Technology/Wellcome Images)

A group of costumed fans attend Comic-Con International at San Diego Convention Center on July 12, 2015 in San Diego, California. (Photo by Daniel Knighton/Getty Images)

Workers attach a hat to a pinata depicting the drug lord Joaquin “El Chapo” Guzman at a workshop in Reynosa, July 21, 2015. Guzman broke out of Mexico's top maximum security prison through a tunnel built into his cell earlier this month. (Photo by Daniel Becerril/Reuters)

Argentine Juan Manuel Silva and Pablo Sisterna (not pictured) crash in their Mercedes car during the 7th stage of the Dakar Rally from Iquique to Uyuni, January 10, 2015. (Photo by Daniel Rodrigo/Reuters)

A Comic Con attendee poses during the 2014 New York Comic Con at Jacob Javitz Center on October 9, 2014 in New York City. (Photo by Daniel Zuchnik/Getty Images)

Visitors look at penguins wearing Santa Claus (in red) and Christmas tree (in green) costumes during a promotional event for Christmas at an amusement park in Yongin, south of Seoul, December 18, 2013. (Photo by Kim Hong-Ji/Reuters)

The Northern Lights glow green in a spectacular light show above a field of trees frozen solid with snow. (Photo by Jaak Sarv/Solent News & Photo Agency)

Women perform a pole dancing routine during the national day celebration of “Urban Pole” dance along a street in Monterrey, Mexico, on June 9, 2013. (Photo by Daniel Becerril/Reuters)