Ozawa Makoto, Suzuki Yasuyuki, Nomura Taishin
Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka, Japan.
Front Hum Neurosci. 2022 May 12;16:842883. doi: 10.3389/fnhum.2022.842883. eCollection 2022.
Involuntary eye movement during gaze (GZ) fixation, referred to as fixational eye movement (FEM), consists of two types of components: a Brownian motion like component called drifts-tremor (DRT) and a ballistic component called microsaccade (MS) with a mean saccadic amplitude of about 0.3° and a mean inter-MS interval of about 0.5 s. During GZ fixation in healthy people in an eccentric position, typically with an eccentricity more than 30°, eyes exhibit oscillatory movements alternating between centripetal drift and centrifugal saccade with a mean saccadic amplitude of about 1° and a period in the range of 0.5-1.0 s, which has been known as the physiological gaze-evoked nystagmus (GEN). Here, we designed a simple experimental paradigm of GZ fixation on a target shifted horizontally from the front-facing position with fewer eccentricities. We found a clear tendency of centripetal DRT and centrifugal MS as in GEN, but with more stochasticity and with slower drift velocity compared to GEN, even during FEM at GZ positions with small eccentricities. Our results showed that the target shift-dependent balance between DRT and MS achieves the GZ bounded around each of the given targets. In other words, GZ relaxes slowly with the centripetal DRT toward the front-facing position during inter-MS intervals, as if there always exists a quasi-stable equilibrium posture in the front-facing position, and MS actions pull GZ intermittently back to the target position in the opposite direction to DRT.
注视（GZ）固定期间的非自主眼球运动，称为注视性眼球运动（FEM），由两种成分组成：一种类似布朗运动的成分称为漂移-震颤（DRT），以及一种弹道成分称为微扫视（MS），其平均扫视幅度约为0.3°，平均微扫视间隔约为0.5秒。在健康人处于偏心位置（通常偏心度大于30°）的GZ固定过程中，眼睛表现出振荡运动，在向心漂移和离心扫视之间交替，平均扫视幅度约为1°，周期在0.5 - 1.0秒范围内，这被称为生理性注视诱发眼震（GEN）。在此，我们设计了一种简单的实验范式，即GZ固定在从正前方位置水平移动且偏心度较小的目标上。我们发现，即使在偏心度较小的GZ位置的FEM期间，也存在与GEN中类似的向心DRT和离心MS的明显趋势，但与GEN相比具有更多的随机性且漂移速度较慢。我们的结果表明，DRT和MS之间依赖于目标移动的平衡实现了围绕每个给定目标的GZ边界。换句话说，在微扫视间隔期间，GZ随着向心DRT缓慢放松至正前方位置，就好像在正前方位置始终存在一个准稳定平衡姿势，并且微扫视动作将GZ间歇地拉回到与DRT相反方向的目标位置。
