Periodically throughout recorded history, puzzling instances of psychiatric and neurologic symptoms have presented en mass<span>: outbursts of thrashing and screaming, or je rky spasms and abrupt vocal tics affecting a group of individuals at once and often attributed to causes like possession, witchcraft, and malingering. Such occurrences of so-called "mass hysteria" continue to confound the medical community, but growing experience has improved the understanding and approach to these seemingly contagious psychogenic events. </span>
