Rhesus Monkeys Can Learn to Recognize Themselves in a Mirror Like Humans

Unlike humans and great apes, Rhesus monkeys don't realize that their own face stares back at them when they look in the mirror. Now, though, scientists have discovered that they can learn that it's a reflection. Not only that, but once they learn these monkeys spontaneously use mirrors to look at themselves.

"Our findings suggest that the monkey brain has the basic 'hardware' [for mirror self-recognition], but they need appropriate training to acquire the 'software' to achieve self-recognition," said Neng Gong, one of the researchers, in a news release.

In this latest study, the researchers placed rhesus monkeys in front of a mirror and shined a mildly irritating laser light on the monkeys' faces. After two to five weeks of the training, the monkeys had learned to touch face areas marked by a spot they couldn't feel in front of a mirror. They also noticed virtual face marks in mirroring video images on a screen. In other words, they learned to mass the standard mark test for mirror self-recognition.

That's not all, either. Most of the trained monkeys-a total of five out of seven-later showed typical mirror-induced self-directed behaviors. For example, they touched the mark on their face or ear and then looked at or smelled their fingers, as if wondering exactly what was on their face. The monkeys also used the mirrors in other ways that were no prompted by the researchers to inspect other body parts.

"Although the impairment of self-recognition in patients implies the existence of cognitive/neurological deficits in self-processing brain mechanisms, our findings raised the possibility that such deficits might be remedied via training," write the researchers. "Even partial restoration of self-recognition ability could be desirable."

The findings are published in the journal Current Biology.

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