Invariance of vestibulo-ocular reflex gain to head impulses in pitch at different initial eye-in-orbit elevations: implications for Alexander's law.
CONCLUSIONS
These findings are in line with previous data on the horizontal vestibulo-ocular reflex (VOR) from this laboratory and suggest that eye position signals do not modulate natural vestibular responses. Hence, the Alexander's law (AL) phenomenon cannot be interpreted simply as a consequence of vestibular or oculomotor nuclei activity modulation with desired gaze.


BACKGROUND
AL states that the intensity of the spontaneous nystagmus of a patient with a unilateral vestibular lesion grows with increasing gaze in the direction of the fast phase. Some of the mechanisms proposed to account for the gaze effects assume a direct modification of the normal VOR by eye position signals. We tested the validity of these assumptions and investigated the effects of gaze direction on the normal vertical human VOR in the behaviorally relevant high frequency range.


METHODS
Head and eye movements were recorded with the search coil method during passive head impulses in pitch, while subjects were asked to hold gaze at various elevation angles in 8° steps within ± 16° from the straight ahead reference position.


RESULTS
Upward and downward head rotations produced VOR gains of similar magnitude. Furthermore, the gain remained unaffected by eye-in-orbit position for both upward and downward head impulses.
Dizziness and Balance Unit, Department of Physiology, School of Nursing, University of Athens, Greece. dimitrianstas@yahoo.com
Dimitri
D
Anastasopoulos
Evangelos
E
Anagnostou
D000328:Adult; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009760:Nystagmus, Physiologic; D012016:Reference Values; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D012399:Rotation; D012494:Sampling Studies; D014741:Video Recording