Morris J. Lewis discovered the jaw jerk reflex in 1885
Edward J. FINE1,2 and Linda LOHR2
OBJECTIVES: To trace the history of the jaw jerk reflex (JJR): substantiate its discovery by the American neurologist, Morris James Lewis, MD, PhD (1852-1928), examine the specious claim for discovery by British neurologist, Armand de Watteville (ADW) and elucidate the physiology of this reflex.
BACKGROUND: ADW (1846-1925) is commonly but incorrectly credited with discovery of the human jaw jerk reflex (JJR) in 1886, based on his note in Brain 8:518-519, 1886. ADW stated that the JJR was increased in a case of amyotrophic lateral sclerosis (ALS). A reference in Charles K. Mills' The Nervous System and its Disease to a paper by written by Morris J. Lewis (MJL) in 1885 (1) could cast doubt upon de Watteville's claim for discovery of the JJR.
DESIGN/METHODS: Reviews of American text books of neurology from 1884 to 1898, Surgeons' General Index, files on MJL at College of Physicians and Wistar Institute Philadelphia, USA. Recording the JJR in several normal subjects using modern EMG equipment.
RESULTS: ADW elicited the JJR, by introducing "a tongue depressor or paper knife in the mouth" and striking "either object with a thin bound book or best of all with a percussion hammer". The index patient was a woman with ALS who exhibited an increased JJR. Dr. Charles Beevor published details of her clinical course in a companion article. ADW stated that the JJR had been observed "in a case in America", but offered no reference. A bibliographic reference by Charles K. Mills (1) established that MJL observed the JJR before May 9, 1885. Lewis described the JJR as "the elevation of the lower jaw immediately following a blow upon the lower teeth or chin" and elicited the JJR by "striking these parts in downward direction with a rubber plexor." The patient's "mouth is open and the muscles should be relaxed." MJL observed the JJR in two patients with spastic paralysis, patient with cerebral tumor and another patient with "congested spinal cord." Lewis elicited the JJR "occasionally from perfectly healthy individuals." (1) He noted that contraction of the masseter or temporalis muscles contributed to the closure of the mouth during JJR. Currently the JJR is obtained by striking the chin with a percussion hammer containing a pressure actuated electric switch to trigger an electromyography (EMG) machine. Electrodes placed on both masseter muscles pick up efferent action potentials in response to afferent activation of stretch receptors by hammer strikes. To obtain the JJR, mandibular muscles must be relaxed. The 7-10 ms average latency and 200-400 [micro]V amplitude were measured from the oscilloscope display of an EMG machine.
CONCLUSION: MJL discovered the JJR, based on earlier publication and description of more patients than ADW.
REFERENCE: (1) Lewis MJ. Med Surg Reporter. 52:591, 1885.
Session VII -- Clinical Neurology and Neurosurgery
Providence, Rhode Island, USA