The group of reflexes collectively known as "primitive reflexes", reviewed by Schott and Rossor,2 include the grasp, snout, palmomental, and rooting reflexes. They are usually associated with neurodegenerative diseases causing dementia and, as the authors point out, loosely linked to frontal lobe pathology, but their exact physiological and anatomical substrates are poorly understood.
The well known tactile-evoked rooting reflex is the movement of both lips towards the examiner’s finger when stroking the lateral side of the upper lip. However, there has been very little written about the related phenomenon of visually-evoked rooting.
Visually-evoked rooting is an extreme form of primitive reflex which is very rarely seen by neurologists. Its real frequency is unknown, presumably because it is only present in advanced stages of dementia in institutionalised patients who are rarely comprehensively examined by a consultant neurologist or elderly care physician. It appears similar to the behaviour of ungulates when approached with an open hand containing food. It seems possible that visually-evoked rooting is different from the more classical tactile rooting reflex which is seen in normal human infants from about 28 weeks in utero until 16 weeks post term.3 Although visual rooting has been reported in childhood autism,4 it is not present in normal young adults.5 Visually-evoked rooting may be more akin to the Babinski sign which van Gijn and others have viewed as a phylogenetically primitive type of flexor synergy withdrawal response of the leg.6,7
Visually-evoked rooting is an extreme form of primitive reflex which is very rarely seen by neurologists
We suspect this extraordinary physical sign is as unfamiliar to most neurologists and elderly care physicians as it was to ourselves.
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