He enriched the oxygen or the carbon dioxide in the air breathed by experimental subjects and found not a hint of suppression or exacerbation of yawning compared with control subjects breathing normal air.

WSJ: Matt Ridley on Why You Just Yawned | Mind & Matter

We found that, compared with 32 normal people in a control group, psychopaths had an 18% smaller amygdala, which is critical for emotions like fear and is part of the neural circuitry underlying moral decision-making.

WSJ: Neurocriminology: Inside the Criminal Mind