A rat neuron before (top) and after (bottom) ketamine treatment. The increased number of orange nodes are restored connections in the rat's brain. Ronald Duman/Yale University hide caption

A page from Pacioli's math encyclopedia, Summa de Arithmetica, Geometria, Proportioni et Proportionalita. via Jane Gleeson-White hide caption

A voter registration form and absentee ballot application at a Franklin County polling place in Columbus, Ohio, on Tuesday. The deadline to register to vote in Ohio is Oct. 9. Matt Sullivan/Reuters/Landov hide caption

Each of these mouse pups was born from an egg scientists created using embryonic stem cells. It's possible the technology could change future treatment for human infertility. Katsuhiko Hayashi hide caption

Pakistani pop singer Shehzad Roy (right) sings for teenage prisoners at a prison in Karachi, Pakistan, in 2008. Known originally for fluffy pop songs, Roy's music has taken a harder, more political edge, protesting injustice in Pakistan. Shakeel Adil/AP hide caption