Affective motor pathways

Output of the amygdala goes to the hypothalamus and a variety of brainstem structures which organize arousal, motor and visceral aspects of emotions. Facial expressions engendered via emotions—smiling, crying and so forth—are brought about via extrapyramidal motor pathways which run in the brainstem reticular formation. The patients with unilateral, damage to corticobulbar fibers descending from the motor cortex have voluntary motor paresis on the different side.  When asked to smile on demand their smile is lopsided. Though, when genuinely amused their smile is bilateral and natural (Duchenne smile) because different emotion-driven motor pathways are engaged.