Barton Holmes, 2, sits with his father, Kevin Holmes, and his mother, Catherine McEaddy Holmes, during an appointment at Children's National Medical Center in Washington, D.C.
Despite significant advances in neurology and imaging, researchers still don't have simple lab tests for diagnosing patients with mental disorders. Diagnoses are still mostly based on a patient's signs and symptoms.
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Although a flying pig doesn't exist in the real world, our brains use what we know about pigs and birds — and superheroes — to create one in our mind's eye when we hear or read those words.