Here is a helpful article from the NYT.

The takeaway: Tantrums are a stress response involving the "lizard" brain. The amygdala (emotions), and they hypothalamus (heart rate, temperature). Adults have similar responses, but our developed pre-frontal cortex helps us to regulate our reactions (most of the time).

What to do?

• Don't try reasoning. The brain in a tantrum cannot reason.
• Manage your emotions - step away (if possible) if you need to calm yourself. If you are calm, your child may mirror your emotional state.
• Send out warm and empathic vibes - remember that your child's amygdala is screaming DANGER!! emphasize that he/she is safe.
• Try some self-soothing strategies and tools BEFORE tantrums strike to see if your child can access these during the tantrum. Remember, this too shall pass.