Blinking and the Brain: Pathways and Pathology

A blink is a rapid bilateral eyelid closure and co-occurring eye movement. The eyes rotate down towards the tip of the nose and back up again. Seemingly, this generally unnoticed often repeated action is not very spectacular. However, if not for the occasional blink we would all be blind. A blink is an interesting phenomenon worth investigating. Through its role as a protective barrier for the eye and as a distributor of the eye’s tearfi lm, blinking is a necessity for our well-being but is also an important tool for neuroscience research and physicians. It is an extremely useful model to study motor performance, motor control, synaptic plasticity and is an excellent physiological instrument for the assessment of internal networks and nuclei [Nishimura, T. and Mori, K, 1996]. The blink rate, refl ex blink characteristics and learned blinks are the three main parameters that can be studied to this end. The blink rate is the frequency with which spontaneous blinks occur and can give information about the dopaminergic system [Karson 1988] and might even be usable as a measure of fatigue [Stern et al. 1994]. The refl ex blink is a rapid involuntary response evoked by external stimulation of the eye or eyelid. It has a protective function and is for instance used in research and physiological tests that use the blink to provide important information on the integrity of afferent and efferent pathways. However, important gaps remain in the knowledge of pathways underlying blinking, and aberrations in pathways or compensatory mechanisms are not fully understood. The learned blink is acquired during eyeblink or eyelid conditioning in which an involuntary blink-evoking stimulus is repeatedly combined with a neutral stimulus. After training the neutral stimulus can evoke the learned blink.