What causes hiccups and why are they so hard to stop?

The answer

Hiccups are involuntary spasmodic contractions of the diaphragm and intercostal muscles followed by a sudden closure of the glottis (the 'hic' sound), occurring at a rate of about 4 to 60 per minute. The reflex is controlled by a 'hiccup center' involving the brainstem, phrenic nerve, and vagus nerve. One prominent evolutionary theory proposes that hiccups are a vestige of the amphibian gill ventilation reflex: tadpoles use a remarkably similar motor pattern to pump water over their gills while closing the glottis to prevent water from entering the lungs. Common triggers include stomach distension, rapid eating, carbonated drinks, and sudden temperature changes. The hiccup reflex is notoriously difficult to stop because it operates via a brainstem circuit largely below conscious control, though many folk remedies work by stimulating the vagus nerve or disrupting the reflex arc.