Laughing and Crying
Brainstem Vocal Bursts, Duchenne Eye Crinkles, and Emotional Tear Chemistry
Neuroscientist Robert Provine analyzed thousands of laugh recordings and showed in 1996 that human laughter follows a rigid, species-wide acoustic signature. Every laugh consists of short, vowel-like notes lasting 75 milliseconds that repeat at regular 210-millisecond intervals in a falling decrescendo. That intrinsic brainstem rhythm prevents speakers from laughing ha-ho-ha-ho.
When Provine covertly logged 1,200 natural conversations in public shopping malls and university sidewalks, fewer than 20 percent of laughs followed anything resembling a formal joke or humorous story. Over 80 percent of laughter occurred after ordinary statements such as polite farewells. Laughter functions primarily as an involuntary acoustic signal of social affiliation.
French neurologist Guillaume Duchenne used electrical muscle stimulation in 1862 to separate voluntary social smiles from spontaneous emotional laughter. Polite cortical smiles contract only the zygomaticus major muscle to pull the lip corners upward. Limbic emotional laughter also recruits the lateral orbicularis oculi muscle, crow-footing the skin around the eyes.
Neurological lesions reveal two anatomically separate vocal circuits in the human brain. Stroke damage to the primary motor cortex paralyzes one side of the face when a patient is asked to smile for a camera. Yet telling that same patient a joke triggers a symmetrical smile and laugh via the anterior cingulate and periaqueductal gray.
Spontaneous belly laughter overrides medullary respiratory homeostasis, firing the abdominal wall and internal intercostal muscles in rhythmic 5-Hertz expiratory bursts. Intrathoracic pressure spikes to $100\text{ mmHg}$ while expiratory airflow jets reach 100 kilometers per hour. Repeated expiratory blasts rapidly empty functional residual lung capacity until the speaker is left gasping for air.
Even in healthy individuals, intense laughter briefly suppresses the Hoffmann spinal reflex (H-reflex), causing the knees to buckle and grip strength to drop. In patients with Type 1 narcolepsy lacking hypothalamic orexin neurons, a sudden laugh removes brainstem monoaminergic tone. Full REM-like glycine muscle atonia then paralyzes the posture while the person remains wide awake.
Sarah-Jayne Blakemore, Daniel Wolpert, and Chris Frith demonstrated using functional brain imaging in 1998 why self-tickling fails to provoke laughter. When the motor cortex commands the fingers to poke the ribs, the cerebellum sends a predictive efference copy to the somatosensory cortex. That prediction subtracts the expected touch sensation before the fingers arrive.
Marina Davila Ross recorded acoustic spectrograms of tickled infant orangutans, gorillas, chimpanzees, bonobos, and human babies in 2009 to reconstruct the evolutionary tree of laughter. Great apes produce laughter by panting both inward and outward. Humans evolved unidirectional expiratory laughter alongside the sustained subglottal breath control required for speech.
Ophthalmologists divide human lacrimation into three biochemically distinct secretions from the same almond-shaped lacrimal gland. Basal tears continuously lubricate the cornea at one microliter per minute, while reflex tears flush irritants like onion syn-propanethial-S-oxide upon trigeminal nerve stimulation. Psychic emotional tears—unique to Homo sapiens—flow strictly from limbic distress or relief.
Biochemist William Frey collected tears from volunteers watching tragic films versus slicing raw onions in 1981 and found that emotional tears carry 24 percent higher protein concentration than reflex tears. Psychic tears are selectively enriched with stress-linked anterior pituitary prolactin, adrenocorticotropic hormone (ACTH), and the endogenous opioid painkiller leucine-enkephalin.
When emotional lacrimation surges tenfold from 1 microliter per minute to over 100 microliters per minute, tear volume overwhelms corneal evaporation and spills over the lower eyelid margin. Excess tears drain through two medial puncta into the nasolacrimal duct, emptying directly beneath the inferior nasal turbinate as a watery runny nose.
The aching lump felt in the throat right before crying—globus pharyngeus—is not a physical obstruction. Sympathetic fight-or-flight arousal demands a wide-open glottis to maximize oxygen intake, while simultaneous parasympathetic crying signals order the pharynx to contract. That opposing muscular tug-of-war between cricothyroid and pharyngeal constrictors creates the sensation of a block.