耳石性眼反応の特徴―ステップ状側方直線加速度負荷による解析―

Abstract

Lateral linear acceleration induces otolithic nystagmus and the otolith-ocular reflex (OOR). These response properties have been studied mostly by dynamic analysis using sinusoidal translation, and only a few reports are available so far with static analysis using step-mode acceleration, due to technical limitations. According to our studies using a linear accelerator with a period up to several seconds of step-mode lateral oscillation (Mori and Katayama, 1998; Katayama and Mori 2001), the direction of nystagmus is dependent on G-direction and directional preponderance (DP) of nystagmus elicitation is physiological. The slow cumulative eye-position (SCEP) curve in which the fast components are eliminated is saw-toothed in shape when lateral oscillation continues in a step mode, implying that the eye position, instead of the eye velocity, is controlled by stimulus velocity signals. The SCEP often accompanies a slow drift during the oscillation, and the slow-drift slope is positively correlated with DP: the steeper the slope, the larger the DP. The OOR velocity measured from the SCEP slope is symmetrical between G-directions when the slow drift is cancelled algebraically. Such symmetry in OOR velocity is in agreement with the previous reports (Gianna et al., 1997; Lempert et al., 1998 1999) using a short and single step-mode acceleration, suggesting that the slow drift is a component hidden behind the ordinary ocular movement and adjusted by the fast phase of nystagmus.