"I'd have to say never, " he said, smiling with his response.

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Results show that high delayers are more successful at not pressing the button in response to a smiling face.

NEWYORKER: Don��t!

Marco Iacoboni, a lab director at the UCLA Brain Mapping Center, says when people see a smile, so-called mirror neurons fire in their brain and evoke a similar neural response as if they were smiling themselves.

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