History of the discovery, physiology, and clinical use of the blink reflex
Edward J. FINE1 and Christopher VICENTE2
Soon after the blink reflex (BR) was first described by Walker Overend (1858-1926) in a letter to the Editor of Lancet in 1896 (I:619), American neurologist Daniel J. McCarthy (1874-1958) and Russian physiologist Vladmir Bekterev (1857-1927) made acrimonious claims for their individual "discovery" of the BR. This presentation will examine their claims, compare Overend and his competitors' concepts to current knowledge about the physiology and current clinical applications of the BR. Overend noted that" when the skin of the forehead is gently taped with the edge of an ordinary wooden stethoscope, a twitch in the lower eyelid of the same side may be observed ..and while severe percussion elicits a simultaneous movement of the opposite lids".."It is a true skin reflex" and the motor pathway is identical to the conjunctival reflex; the sensory channels lie in the ..supraorbital division of the frontal nerve and the centre is probably located in the midbrain". He noted that the area for eliciting the reflex was more in choreic patients than normal subjects.
In 1901 McCarthy (Neurologische Centralblatt 20:800-1) claimed priority for eliciting reflex contraction of the orbicularis oculi by taping the skin of the forehead with a percussion hammer. He noted that division of the supraorbital nerve extinguished the BR. McCarthy stated that the afferent portion of his reflex was through CN V because sectioning the sensory root of the Gasserian ganglion abolished the reflex. McCarthy concluded that his supra-orbital reflex was identical to a tendon reflex. Also in 1901 Vladmir Bekterev (Neurologische Centralblatt 20:930-6) overlooked Overend's report, disputed McCarthy's claim for priority but concurred with McCarthy that the BR was similar to a tendon reflex and lesions of the sensory root of the trigeminal abolish the reflex.
Erik Kugelberg electrically stimulated the supraorbital nerve, recorded the early latency R1 and the late R2 electromyographic (EMG) responses from orbicularis oculi muscles to confirm that the BR was a cutaneous reflex (Brain 75:385-396). The R1 and R2 of the BR was delayed or abolished by lesions in trigeminal nerve, confirming Overend's original observations about the afferent pathway of the BR. Overend was only partially correct about the anatomy of the BR; synapses for the R1 and R2 responses lie in the pons and medulla and not the midbrain. Overend was proven partially correct by the observation that the BR has a decreased stimulus threshold in chorea. The blink response has been shown to be the initial response of the startle. Currently the BR is used to monitor the function of CN V or VII in surgery for acoustic neuroma, predict the outcome of Bell's palsy, detect occult lesions in multiple sclerosis patients and assess activity of the brainstem reticular formation in patients with disorders of attention and startle. The blink reflex can elicited by mechanical tap, loud sound or electrical stimulus.
These observations favor our contention that Overend should be recognized for priority of discovery and accuracy of most of his observations about the BR.
Session VI -- Anatomical and Physiological Models and Techniques
Los Angeles, California, USA