Ito Y, Corna S, von Brevern M, Bronstein A, Gresty M
Department of Oto-Rhino-Laryngology, Gifu University School of Medicine, Japan.
Exp Brain Res. 1997 Nov;117(2):266-72. doi: 10.1007/s002210050221.
Reflex head-righting in normal and labyrinthine-defective (LD) subjects was compared to identify the relative functional effectiveness of vestibular-collic and cervico-collic myotactic reflexes. To restrict stimuli largely to the head and neck, subjects lay supine, supported up to the shoulders on a horizontal bed with their head supported in a sling over the edge. The head fell freely as the sling was released with an electromagnetic catch. Head drops were delivered with the subjects instructed to relax and accept the fall passively or to actively right the head as fast as possible. With both instructions, righting responses in normal subjects commenced with electromyographic (EMG) bursts in the sternocleidomastoid (SCM) at 24.5 ms latency, which was reflected in a deceleration of the downwards head velocity. The latency of the earliest EMG responses in LD subjects was 67.4 ms, accompanied by similar deceleration. It is assumed that the earliest response in normal subjects is vestibular, whereas in LDs the SCM stretch reflex is the earliest response. These reflexes are followed at circa 100 ms by more intense EMG activity due to voluntary movement, but braking of head fall is evident before voluntary activity takes effect. Righting was more effective in normal subjects than in LDs, and when "active" normal subjects made more vigorous righting responses than when "passive"; whereas active righting in LDs was no better than passive. The results demonstrate that reflex responses contribute significantly to head-righting. The vestibular contribution gives an advantage over stretch reflexes alone and also assists in voluntary enhancement of reflex responses.
对正常受试者和迷路缺陷（LD）受试者的反射性头部扶正进行比较，以确定前庭 - 颈反射和颈 - 颈肌动反射的相对功能有效性。为了将刺激主要限制在头部和颈部，受试者仰卧，肩部以下由水平床支撑，头部由边缘上方的吊带支撑。当用电磁扣松开吊带时，头部自由下落。头部下落时，受试者被指示放松并被动接受下落，或者尽快主动扶正头部。在这两种指示下，正常受试者的扶正反应始于胸锁乳突肌（SCM）的肌电图（EMG）爆发，潜伏期为24.5毫秒，这反映在头部向下速度的减速上。LD受试者最早的EMG反应潜伏期为67.4毫秒，伴有类似的减速。假定正常受试者最早的反应是前庭反应，而在LD受试者中，SCM牵张反射是最早的反应。大约100毫秒后，由于自主运动，会出现更强烈的EMG活动，但在自主活动生效之前，头部下落的制动就很明显。正常受试者的扶正比LD受试者更有效，并且“主动”的正常受试者比“被动”时做出更有力的扶正反应；而LD受试者的主动扶正并不比被动扶正更好。结果表明，反射反应对头部扶正有显著贡献。前庭的贡献比单独的牵张反射更具优势，并且也有助于反射反应的自主增强。
