Vestibular compensation and substitution

This is a very brief update on the major papers since August 1998, Unilater al vestibular loss causes oculomotor, postural and sensory symptoms, all of which would be appropriate responses in a healthy person to a strong maint ained angular and linear acceleration stimulus directed towards the healthy side. Within hours or days these static symptoms (so called because they a re present without any externally imposed vestibular stimulation) reduce, a nd their progressive disappearance is called 'vestibular compensation'. How ever, careful testing with natural vestibular stimuli shows that the dynami c vestibular response after unilateral vestibular loss to passively imposed vestibular stimuli does not recover; it is usually asymmetric and function ally ineffective. Major recent developments are: (1) the permanent asymmetr ical and functionally ineffective dynamic rotational vestibule-ocular refle x responses to passive natural vestibular stimulation after unilateral vest ibular loss and canal blocks in human patients; (2) evidence for the substi tution of other sensory input and responses during vestibular compensation; (3) perceptual testing using visual perception of a horizontal line to con firm permanent otolith dysfunction; (4) the clear and substantial differenc es in post-unilateral vestibular loss vestibule-ocular reflex responses bet ween passive and active head turning; and (5) new results in brainstem phys iology explaining the disappearance of static symptoms. Curr Opin Neurol 13 :27-30. (C) 2000 Lippincott Williams & Wilkins.