Alonso Jose-Manuel
Department of Psychology, University of Connecticut, Storrs 06269, USA.
Neuroscientist. 2002 Oct;8(5):443-56. doi: 10.1177/107385802236967.
A cubic millimeter of primary visual cortex contains about 100,000 neurons that are heavily interconnected by intrinsic and extrinsic afferents. The effort of many neuroanatomists over the past has revealed the general outline of these connections; however, their function remains a mystery. Recently, combined physiological and anatomical approaches are beginning to reveal the role of these connections in the generation of cortical receptive fields. A common theme emerges from all these studies: cortical connections are remarkably specific and this specificity is determined in great extent by the type of connection and the neuronal response properties. Feedforward connections follow relatively rigid rules of wiring selectively targeting neurons with receptive fields matched in position and contrast polarity (thalamus --> cortical layer 4) or position and orientation selectivity (layer 4 --> layers 2 + 3). In contrast, horizontal connections follow more flexible rules connecting distant cells that are not retinotopically aligned and neighboring cells with different orientation preferences. These differences in connectivity may give a hint on how visual stimuli are processed in the primary visual cortex. An attractive hypothesis is that local stimuli use the highly selective feedforward inputs to reliably drive cortical neurons while background stimuli modulate their activity through more flexible horizontal (and feedback) connections.
一立方毫米的初级视觉皮层包含约100,000个神经元，这些神经元通过内在和外在传入神经紧密相连。过去许多神经解剖学家的努力揭示了这些连接的大致轮廓；然而，它们的功能仍然是个谜。最近，生理学和解剖学相结合的方法开始揭示这些连接在皮层感受野形成中的作用。所有这些研究都出现了一个共同的主题：皮层连接非常特异，这种特异性在很大程度上由连接类型和神经元反应特性决定。前馈连接遵循相对严格的布线规则，选择性地靶向感受野在位置和对比极性上匹配的神经元（丘脑→皮层第4层）或位置和方向选择性匹配的神经元（第4层→第2 + 3层）。相比之下，水平连接遵循更灵活的规则，连接非视网膜拓扑对齐的远距离细胞和具有不同方向偏好的相邻细胞。这些连接性的差异可能为初级视觉皮层中视觉刺激的处理方式提供线索。一个有吸引力的假设是，局部刺激利用高度选择性的前馈输入可靠地驱动皮层神经元，而背景刺激则通过更灵活的水平（和反馈）连接调节它们的活动。
