Sharon Dahlia, Grinvald Amiram
Department of Neurobiology and the Center for Studies of Higher Brain Functions, Weizmann Institute of Science, Rehovot 76100, Israel.
Science. 2002 Jan 18;295(5554):512-5. doi: 10.1126/science.1065916.
How does the high selectivity to stimulus orientation emerge in the visual cortex? Thalamic feedforward-dominated models of orientation selectivity predict constant selectivity during the visual response, whereas intracortical recurrent models predict dynamic improvement in selectivity. We imaged the cat visual cortex with voltage-sensitive dyes to measure orientation-tuning dynamics of a large neuronal population. Tuning-curve width did not narrow after response onset, whereas the difference between preferred and orthogonal responses (modulation depth) first increased, then declined. We identified a suppression of the evoked responses, referred to as the evoked deceleration-acceleration (DA) notch, which was larger for the orthogonal response. Furthermore, peak selectivity of the tuning curves was contemporaneous with the evoked DA notch. These findings suggest that in the cat brain, sustained visual cortical processing does not narrow orientation tuning; rather, intracortical interactions may amplify modulation depth and suppress the orthogonal response relatively more than the preferred. Thus, feedforward models and recurrent models of orientation selectivity must be combined.
视觉皮层中对刺激方向的高选择性是如何产生的？丘脑前馈主导的方向选择性模型预测视觉反应期间选择性恒定，而皮层内循环模型预测选择性会动态改善。我们使用电压敏感染料对猫的视觉皮层进行成像，以测量大量神经元群体的方向调谐动态。反应开始后调谐曲线宽度并未变窄，而偏好反应与正交反应之间的差异（调制深度）先增加，然后下降。我们发现了诱发反应的一种抑制现象，称为诱发减速 - 加速（DA）波谷，正交反应的该波谷更大。此外，调谐曲线的峰值选择性与诱发的DA波谷同时出现。这些发现表明，在猫脑中，持续的视觉皮层处理不会使方向调谐变窄；相反，皮层内相互作用可能会放大调制深度，并相对偏好反应而言，对正交反应的抑制作用更强。因此，必须将方向选择性的前馈模型和循环模型结合起来。
