Colagiorgio Paolo, Versino Maurizio, Colnaghi Silvia, Quaglieri Silvia, Manfrin Marco, Zamaro Ewa, Mantokoudis Georgios, Zee David S, Ramat Stefano
Department of Electrical, Computer and Biomedical Engineering, University of Pavia, Pavia, Italy.
Department of Brain and Behavioral Sciences, University of Pavia, Pavia, Italy.
J Neurophysiol. 2017 Jun 1;117(6):2324-2338. doi: 10.1152/jn.00864.2016. Epub 2017 Apr 12.
In response to passive high-acceleration head impulses, patients with low vestibulo-ocular reflex (VOR) gains often produce covert (executed while the head is still moving) corrective saccades in the direction of deficient slow phases. Here we examined 23 patients using passive, and 9 also active, head impulses with acute (< 10 days from onset) unilateral vestibular neuritis and low VOR gains. We found that when corrective saccades are larger than 10°, the slow-phase component of the VOR is inhibited, even though inhibition increases further the time to reacquire the fixation target. We also found that ) saccades are faster and more accurate if the residual VOR gain is higher, ) saccades also compensate for the head displacement that occurs during the saccade, and ) the amplitude-peak velocity relationship of the larger corrective saccades deviates from that of head-fixed saccades of the same size. We propose a mathematical model to account for these findings hypothesizing that covert saccades are driven by a desired gaze position signal based on a prediction of head displacement using vestibular and extravestibular signals, covert saccades are controlled by a gaze feedback loop, and the VOR command is modulated according to predicted saccade amplitude. A central and novel feature of the model is that the brain develops two separate estimates of head rotation, one for generating saccades while the head is moving and the other for generating slow phases. Furthermore, while the model was developed for gaze-stabilizing behavior during passively induced head impulses, it also simulates both active gaze-stabilizing and active gaze-shifting eye movements. During active or passive head impulses while fixating stationary targets, low vestibulo-ocular gain subjects produce corrective saccades when the head is still moving. The mechanisms driving these covert saccades are poorly understood. We propose a mathematical model showing that the brain develops two separate estimates of head rotation: a lower level one, presumably in the vestibular nuclei, used to generate the slow-phase component of the response, and a higher level one, within a gaze feedback loop, used to drive corrective saccades.
对于被动性高加速度头部冲动，前庭眼反射（VOR）增益较低的患者通常会在头部仍在移动时产生向慢相不足方向的隐蔽（执行时）纠正性扫视。在此，我们对23例患有急性（发病<10天）单侧前庭神经炎且VOR增益较低的患者进行了被动头部冲动检查，对其中9例患者还进行了主动头部冲动检查。我们发现，当纠正性扫视大于10°时，VOR的慢相成分会受到抑制，尽管这种抑制会进一步增加重新获得注视目标的时间。我们还发现：如果残余VOR增益较高，扫视会更快且更准确；扫视还会补偿扫视期间发生的头部位移；较大纠正性扫视的幅度 - 峰值速度关系与相同大小的头部固定扫视不同。我们提出了一个数学模型来解释这些发现，假设隐蔽性扫视由基于使用前庭和前庭外信号对头部位移的预测的期望注视位置信号驱动，隐蔽性扫视由注视反馈回路控制，并且VOR指令根据预测的扫视幅度进行调制。该模型的一个核心且新颖的特征是，大脑会形成两种独立的头部旋转估计，一种用于在头部移动时产生扫视，另一种用于产生慢相。此外，虽然该模型是为被动诱导头部冲动期间的注视稳定行为而开发的，但它也模拟了主动注视稳定和主动注视转移眼动。在固定静止目标时进行主动或被动头部冲动期间，前庭眼增益较低的受试者在头部仍在移动时会产生纠正性扫视。驱动这些隐蔽性扫视的机制尚不清楚。我们提出了一个数学模型，表明大脑会形成两种独立的头部旋转估计：一种较低层次的估计，可能在前庭核中，用于产生反应的慢相成分；另一种较高层次的估计，在注视反馈回路内，用于驱动纠正性扫视。
