Hatta S, Kumagami T, Qian J, Thornton M, Smith E L, Chino Y M
Department of Ophthalmology, Tottori University School of Medicine, Yonago, Japan.
Invest Ophthalmol Vis Sci. 1998 Nov;39(12):2259-67.
Optokinetic nystagmus (OKN) in young infants typically shows a temporal-to-nasal asymmetry under monocular viewing conditions. The neural basis for this asymmetry has been a matter of debate. One idea is that the OKN asymmetry reflects a similar asymmetry in the directional sensitivity of primary visual cortical (V1) neurons. An alternative hypothesis is that the OKN asymmetry is due to an immaturity in the ability of cortical neurons to influence the activity of subcortical structures that directly control OKN. We addressed this issue by studying the directional sensitivity of V1 neurons in young infant monkeys.
The neuronal activity of V1 units was recorded from anesthetized and paralyzed rhesus monkeys ranging in age from 6 days to 8 weeks using standard extracellular single-unit recording methods. For comparison, V1 units from normal adult monkeys were also studied. Using drifting sinusoidal gratings of the optimal spatial frequency and a moderate contrast, we measured the responsiveness of individual units to 24 directions of stimulus movement. The preferred stimulus direction and the magnitude of the directional response bias were determined by a vector summation method.
No clear signs of nasotemporal asymmetries in direction tuning were found in our cell population from infant monkeys. However, the overall directional sensitivity and the peak monocular response amplitudes of these units were significantly lower, and binocular suppression was greater during the first 4 weeks of life than in adults.
The OKN asymmetry in young infants may be more closely associated with the lower overall directional sensitivity and the subnormal responsiveness of V1 neurons rather than with an obvious asymmetry in the directional properties of V1 neurons.
在单眼观察条件下，幼儿的视动性眼震（OKN）通常表现出颞侧到鼻侧的不对称性。这种不对称性的神经基础一直存在争议。一种观点认为，OKN不对称反映了初级视皮层（V1）神经元方向敏感性的类似不对称。另一种假设是，OKN不对称是由于皮层神经元影响直接控制OKN的皮层下结构活动的能力不成熟所致。我们通过研究幼猴V1神经元的方向敏感性来解决这个问题。
使用标准的细胞外单单位记录方法，从6天至8周龄的麻醉和瘫痪恒河猴中记录V1单位的神经元活动。为了进行比较，还研究了正常成年猴的V1单位。使用最佳空间频率和中等对比度的漂移正弦光栅，我们测量了单个单位对24个刺激运动方向的反应性。通过矢量求和法确定首选刺激方向和方向反应偏差的大小。
在我们的幼猴细胞群体中，未发现方向调谐存在明显的鼻颞不对称迹象。然而，这些单位的总体方向敏感性和单眼反应峰值幅度明显较低，并且在出生后的前4周内双眼抑制比成年猴更强。
幼儿的OKN不对称可能与V1神经元较低的总体方向敏感性和反应性异常更为密切相关，而不是与V1神经元方向特性的明显不对称有关。
