The tripartite origins of the tonic neck reflex: Gesell, Gerstmann, and Magnus.

The standard neurologic examination of the newborn and infant includes the elicitation of the tonic neck reflex. Normally present, its persistence is suggestive of neurologic dysfunction and a prognostic marker highly suggestive of an adverse outcome. Working in different fields, with different approaches and largely independently, three leaders of early 20th century neurosciences (Rudolf Magnus, Josef Gerstmann, and Arnold Gesell) elaborated different aspects of this primitive reflex. Magnus provided the first description in an animal model utilizing a meticulously prepared decerebrate cat correctly identifying the reflex's reliance on proprioceptors in the neck and processing in the upper cervical segment. Gerstmann first described its occurrence in the setting of neurologic disease, providing a meticulous written description in an early description of the index case of what would later be eponymously designated Gerstmann-Straussler-Scheinker syndrome. Gesell initially described the reflex's fundamental occurrence in normal young infants, highlighting its adaptive role in early development and its persistence as a hallmark of neurologic pathology.