Ferster D, Miller K D
Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208, USA.
Annu Rev Neurosci. 2000;23:441-71. doi: 10.1146/annurev.neuro.23.1.441.
The origin of orientation selectivity in the responses of simple cells in cat visual cortex serves as a model problem for understanding cortical circuitry and computation. The feed-forward model posits that this selectivity arises simply from the arrangement of thalamic inputs to a simple cell. Much evidence, including a number of recent intracellular studies, supports a primary role of the thalamic inputs in determining simple cell response properties, including orientation tuning. This mechanism alone, however, cannot explain the invariance of orientation tuning to changes in stimulus contrast. Simple cells receive push-pull inhibition: ON inhibition in OFF subregions and vice versa. Addition of such inhibition to the feed-forward model can account for this contrast invariance, provided the inhibition is sufficiently strong. The predictions of "normalization" and "feedback" models are reviewed and compared with the predictions of this modified feed-forward model and with experimental results. The modified feed-forward and the feedback models ascribe fundamentally different functions to cortical processing.
猫视觉皮层中简单细胞反应的方向选择性起源，是理解皮层回路和计算的一个典型问题。前馈模型假定，这种选择性仅仅源于丘脑输入到简单细胞的排列方式。包括最近一些细胞内研究在内的大量证据，支持丘脑输入在决定简单细胞反应特性（包括方向调谐）方面的主要作用。然而，仅靠这一机制无法解释方向调谐对刺激对比度变化的不变性。简单细胞接受推挽式抑制：在OFF子区域有ON抑制，反之亦然。只要抑制足够强，将这种抑制添加到前馈模型中就可以解释这种对比度不变性。本文回顾了“归一化”和“反馈”模型的预测，并将其与这种修正的前馈模型的预测以及实验结果进行了比较。修正的前馈模型和反馈模型赋予皮层处理截然不同的功能。
