Laughter is a complex vocal expression of positive emotion which is ubiquitous in human behavior. It serves several social functions like diffusing tension and strengthening bonds. Laughter is also pleasurable and activates ancient brain circuits related to reward and social affiliation [1][2][6].

Neuroimaging studies show that humorous stimuli engage key nodes of the brain’s mesolimbic dopamine system, including the ventral tegmental area and nucleus accumbens [3]. This is similar to patterns seen with other natural reinforcers like food, sex, and social bonding [4]. This helps explain why humor is intrinsically rewarding and potentially addictive. Production of laughter requires coordinated contractions of respiratory muscles under partial volitional control, facilitated by motor planning regions like the supplemental motor cortex [5].

The motor cortex has connections to brainstem areas controlling respiration and vocalization, allowing modulation of involuntary laugh patterns [6]. Contagious spread of laughter may utilize pathways linking auditory cortex to frontal lobe mirror neurons specialized for mimicry [2]. Given its deep evolutionary roots in social bonding, laughter likely emerged early in mammalian evolution [1].

Sources:

1-3, 6. Wickens, A. (2005). Foundations of biopsychology (2nd ed.). Pearson/Prentice Hall.

4-5. Panksepp, J. & Biven, L. (2012). The archaeology of mind: Neuroevolutionary origins of human emotions. W.W. Norton & Company.