视觉神经表征中底-顶和顶-底的双向激活——来自人与猴的实验证据

Bi-directional Activation of Neural Representation in Vision:Bottom-up and Top-down Activation—Experimental Evidences from Human and Monkey

长期以来 ,建立在坚实生理学证据之上的底 顶加工说和特征检测理论在视觉研究中占主导地位。对于顶 底加工人们只能靠一般常识 ,即知识或经验通过激活记忆中的神经表征影响视觉过程。但是近年来 ,来自人和猴的研究为顶 底的加工提供了实验证据。首先位于猴腹侧加工系统内的物体和面孔视觉记忆表征 ,提供了神经编码是怎样创立、组织和再激活的最佳实验证据。联想性编码是通过学习由一些具有特殊功能的神经元建立的 ,这些神经元具有将时间性关联刺激的表征联系起来的能力。其次 ,不仅来自视网膜的底 顶信号 ,而且来自前额叶的顶 底信号都能触发联想性编码的提取 ,既可以作为有意识回忆的神经基础 ,又是顶 底加工影响视觉过程的基础。脑损伤病人研究、具有高时间分辨率的人类功能性核磁共振成像 (functionalmagneticresonanceimaging ,fMRI)和猴fMRI研究以及猴细胞电生理分析相结合 ,将进一步加强人们对视觉脑机制的全面理解。

Bottom-up processing and feature detecting theory based on strong electrophysiological evidences has played a dominant role in the visual research for long time.People know top-down processing just by common sense.Knowledge or experience are recalled from memory by reactivation of their neural representations and affected visual processes.However recently,researches from human and monkey provide experimental evidences for top-down processing.First,mnemonic representation of visual objects and faces,located in the ventral processing stream of visual perception in monkey,provide the best evidences of how neuronal codes are created by neurons that have the special ability to link the representations of temporally associated stimuli;second,experiments suggest that not only bottom-up signals from the retina but also top-down signals from the prefrontal cortex can trigger the retrieval of associative codes,which may serve as a neural basis both for the conscious recall and for the visual processes affected by top-down processing Further studies will improve people's understanding of the causal relation of activation and behavior by use of combined fMRI and electrophysiology or lesion studies.