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Barbecue Whole‐Body Position Modulates Cerebellar Downbeat Nystagmus
Author(s) -
MARTI SARAH,
PALLA ANTONELLA,
STRAUMANN DOMINIK
Publication year - 2003
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.2003.tb00266.x
Subject(s) - annals , clinical neurology , neurology , medicine , humanities , psychology , philosophy , classics , art , psychiatry , neuroscience
Downbeat nystagmus is a frequent ocular motor sign in patients with lesions of the vestibulocerebellum.1 Upward drift in cerebellar downbeat nystagmus is caused by two concurrent mechanisms1,2: (1) a gaze-evoked drift due to a leaky vertical neural integrator, and (2) an upward-directed velocity bias independent of vertical gaze eccentricity and already present with “gaze straight ahead.” Recently, we have shown that the velocity bias, that is, the vertical drift in gaze straight ahead, consists of two components3: (1) a gravity-dependent component that sinusoidally modulates as a function of whole body position along the pitch plane, and (2) a gravity-independent component that is directed upward. The combination of these two components leads to an overall vertical drift that is minimal in supine and maximal in prone position. In the roll plane, however, no modulation of the vertical drift occurs; that is, the vertical velocity bias is approximately the same in upright and 90° ear-down body positions. Healthy subjects showed a similar sinusoidal modulation of the vertical drift velocity as a function of whole-body position, but in a scaled-down manner. In upright and ear-down positions, the overall drift mainly consists of the gravityindependent component. In the supine position, the gravity-dependent component is directed downward and opposes the gravity-independent component, which is always directed upward. Thus, the overall vertical drift in both upright and ear-down positions is faster than in supine position. As a result, even though the gravity-dependent component modulates only along the pitch plane, changing whole-body position about the earth-horizontal yaw axis (barbecue rotation) should modulate downbeat nystagmus. Specifically, upward drift should be faster in the ear-down side positions than in the supine position. FIGURE 1 confirms this hypothesis: vertical drift velocity during gaze straight ahead is plotted as a function of the angular whole-body position about the earthhorizontal yaw axis (barbecue position). In patients with cerebellar atrophy (left panel), the gravity-dependent component modulates sinusoidally and adds to a constant upward-directed, gravity-independent component. The overall drift is maximal in prone position and minimal in supine position, whereas in 90° side positions, the ve-