Dogs who scored well on the Wesen test, which is used to analyze a dog's temperament, tended to have lower levels of cortisol, often called the "stress hormone," and higher levels of serotonin, often called the "happiness hormone," according to a study published in the open-access journal PLOS One b y Minjung Yoon from Kyungpook National University, Republic of Korea, and colleagues. ...read more read less