Department of Experimental Psychology, University of Oxford, Oxford, UK.
Prog Brain Res. 2011;189:95-111. doi: 10.1016/B978-0-444-53884-0.00020-8.
Visual development is a key area for understanding and assessing early brain development. Different levels in the hierarchy of visual processing, from the initial response to flashes of light, through selective responses to contour orientation and motion in primary visual cortex (V1), to global processing in extrastriate of large-scale patterns of form and motion, can each be assessed using stimuli designed to isolate specific neural activity in visual event-related potentials (VERPs). This approach has been used to reveal the sequence of emergence of different visual cortical functions in the first 6 months of typical human development, and to provide early indicators of anomalies in brain development. Delayed or absent onset of orientation-reversal (OR-)VERPs, as a measure of cortical development, has been shown to be a sensitive indicator of perinatal brain damage in both term-born and prematurely born infants. Direction-reversal (DR-)VERPs appear a few weeks later than OR-VERPs in typical development, and are further delayed in even healthy children born preterm, reflecting possible early vulnerability of the motion (dorsal stream) system. High-density recordings of responses to global motion and global form patterns show that these extrastriate systems are typically functional by 5 months of age, but the topography of the activity distributions shows that the brain systems underlying these responses are radically reorganized between infancy and adulthood. In prematurely born infants whose structural brain MRI was evaluated at birth, the onset of the response is absent or delayed in those with severe brain injury, while in those with mild/moderate brain injury the response is present but its spatial organization is further from the adult pattern than those in controls. These findings are related to the development of distinct networks of brain areas in the dorsal and ventral cortical streams, and the apparent vulnerability of the dorsal-stream network in a wide range of both genetic and acquired developmental disorders.
视觉发育是理解和评估早期大脑发育的关键领域。视觉处理层次结构的不同水平，从对光闪烁的初始反应，到选择性地对轮廓方向和初级视觉皮层 (V1) 中的运动做出反应，再到对大尺度形状和运动模式的外纹状皮层的全局处理，都可以使用旨在分离视觉事件相关电位 (VERP) 中特定神经活动的刺激来评估。这种方法已被用于揭示典型人类发育前 6 个月中不同视觉皮层功能的出现顺序，并提供大脑发育异常的早期指标。作为皮质发育的指标，朝向反转 (OR-)VERP 的延迟或缺失出现表明足月和早产儿的围产期脑损伤均具有敏感性。在典型发育中，方向反转 (DR-)VERP 比 OR-VERP 晚出现几周，而即使是早产儿的健康儿童也会进一步延迟，这反映了运动 (背侧流) 系统的早期脆弱性。对全局运动和全局形状模式的反应进行高密度记录表明，这些纹外系统在 5 个月大时通常具有功能性，但活动分布的地形表明，这些反应背后的大脑系统在婴儿期和成年期之间发生了彻底的重组。在出生时进行结构脑 MRI 评估的早产儿中，严重脑损伤的婴儿的反应起始缺失或延迟，而轻度/中度脑损伤的婴儿的反应存在，但空间组织与对照组相比更远离成人模式。这些发现与背侧和腹侧皮质流中大脑区域的不同网络的发育有关，以及广泛的遗传和后天发育障碍中背侧流网络的明显脆弱性。
