Responding to faces is a critical tool for social interactions between humans. Without the ability to read faces and their expressions, it would be hard to tell friends from strangers upon first glance, let alone a sad person from a happy one. Now, neuroscientists from Caltech, with the help of collaborators at Huntington Memorial Hospital in Pasadena and Cedars-Sinai Medical Center in Los Angeles, have discovered a novel response to human faces by looking at recordings from brain cells in neurosurgical patients.