A mysterious kind of nerve cell that has been linked to empathy, self-awareness, and even consciousness resides in Old World monkeys. The finding, published May 10 in Neuron, extends the domain of the neurons beyond humans, great apes and other large-brained creatures and will now allow scientists to study the habits of a neuron that may be key to human self-awareness.

“People have been reluctant to say, but want to believe, that these neurons might be the neural correlate of consciousness,” says neuroscientist and psychiatrist Hugo Critchley of the University of Sussex in England. Finding the neurons in macaques, which can be studied in laboratories, “opens up the possibility to study directly the role of these cells,” he says.

An earlier study saw no signs of the cells, called von Economo neurons, in macaques. But while carefully scrutinizing a small piece of a macaque brain for a different experiment, anatomist Henry Evrard