Submitted on January 15, 2008
Accepted on April 29, 2008
Alexander's Law Revisited
Ben Jeffcoat1, Alexander Shelukhin1, Alexander Fong1, William Mustain1, and Wu Zhou2*
1 Otolarngology and Communicative Sciences, Univ. of Mississippi Medical Center, Jackson, Mississippi, United States
2 Otolarngology and Communicative Sciences, Univ. of Mississippi Medical Center, Jackson, Mississippi, United States; Univ. of Mississippi, United States; Anatomy, University of Mississippi Medical Center, Jackson, Mississippi, United States; Neurology, University of Mississippi Medical Center, Jackson, Mississippi, United States
* To whom correspondence should be addressed. E-mail: wzhou{at}ent.umsmed.edu.
Alexander’s Law states that the slow-phase velocity of the nystagmus caused by unilateral vestibular lesion, increases with gaze in the beat-direction. Two studies have shown that this gaze effect is generalized to the nystagmus caused by unilateral cold water irrigation (Doslak et al, 1982; Robinson et al, 1984). This indicates that the gaze effect is not the result of central changes associated with a peripheral lesion, but rather due to unilateral vestibular peripheral inhibition. In the present study, we show that there is a similar gaze effect on the nystagmus produced by unilateral warm water ear irrigation. Furthermore, we examined the two hypotheses of Alexander’s Law proposed in the two studies. Doslak et al’s hypothesis is based on the gaze-dependent modulation of the VOR response to unbalanced canal input. Robinson et al’s hypothesis, however, is based on the leaky neural integrator caused by unilateral vestibular peripheral inhibition. These two hypotheses predict the same gaze effect on the nystagmus produced by cold water irrigation, but opposite gaze effects on the nystagmus produced by warm water irrigation. Our results support Doslak et al’s hypothesis and suggest that Robinson et al’s hypothesis needs to be modified.
