TONI COLETTE AS TARA: I will be in control, me, Tara. TONI COLETTE AS AN ALTER: This is all your fault. With the drugs. BROOKE GLADSTONE: Our fascination with split personalities goes way back. Think ...

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American In 2015, doctors in Germany reported the ...