What do scientists study in order to people better understand their own personalities

Traits like hobbies,games they like, how much it takes to burst out in anger, 
and how often you are happy mad sad etc.
hope this helps
:)

There are eight major endocrine glands, each with a different function: pituitary gland: the “brain” of the endocrine system; regulates all seven of the other glands and secretes growth hormone.thyroid: regulates a person’s metabolic rate, which is the amount of energy expended daily by a person at rest.thymus: assists in the development of a person’s immune system.adrenal gland: regulates fluid and sodium balance within the body, and secretes epinephrine (“adrenaline”) when the body is under stress, producing the fight-or-flight response.ovaries (in females) and testes (in males): control the development of secondary sex characteristics.pancreatic islets: regulate blood sugar.pineal gland: regulates biorhythms and mood, and stimulates the onset of puberty.