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首页> 外文期刊>Progress in brain research >Bottom-up and top-down dynamics in visual cortex.
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Bottom-up and top-down dynamics in visual cortex.

机译：视觉皮质的自下而上和自上而下的动态。

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A key emergent property of the primary visual cortex (V1) is the orientation selectivity of its neurons. Recent experiments demonstrate remarkable bottom-up and top-down plasticity in orientation networks of the adult cortex. The basis for such dynamics is the mechanism by which orientation tuning is created and maintained, by integration of thalamocortical and intracortical inputs. Intracellular measurements of excitatory and inhibitory synaptic conductances reveal that excitation and inhibition balance each other at all locations in the cortex. This balance is particularly critical at pinwheel centers of the orientation map, where neurons receive intracortical input from a wide diversity of local orientations. The orientation tuning of neurons in adult V1 changes systematically after short-term exposure to one stimulus orientation. Such reversible physiological shifts in tuning parallel the orientation tilt aftereffect observed psychophysically. Neurons at or near pinwheel centers show pronounced changes in orientation preference after adaptation with an oriented stimulus, while neurons in iso-orientation domains show minimal changes. Neurons in V1 of alert, behaving monkeys also exhibit short-term orientation plasticity after very brief adaptation with an oriented stimulus, on the time scale of visual fixation. Adaptation with stimuli that are orthogonal to a neuron's preferred orientation does not alter the preferred orientation but sharpens orientation tuning. Thus, successive fixation on dissimilar image patches, as happens during natural vision, combined with mechanisms of rapid cortical plasticity, actually improves orientation discrimination. Finally, natural vision involves judgements about where to look next, based on an internal model of the visual world. Experiments in behaving monkeys in which information about future stimulus locations can be acquired in one set of trials but not in another demonstrate that V1 neurons signal the acquisition of internal representations. Such Bayesian updating of responses based on statistical learning is fundamental for higher level vision, for deriving inferences about the structure of the visual world, and for the regulation of eye movements.
机译：初级视皮层（V1）的关键突现特性是其神经元的方向选择性。最近的实验表明，在成人皮层的定向网络中，自下而上和自上而下的可塑性非常出色。这种动力学的基础是通过整合丘脑皮质和皮质内输入来创建和维持方向调整的机制。兴奋性和抑制性突触电导的细胞内测量表明，兴奋和抑制在皮质中的所有位置彼此平衡。这种平衡在方向图的风车中心尤为重要，那里的神经元从各种各样的局部方向接收皮质内输入。短期暴露于一种刺激方向后，成人V1中神经元的方向调整会系统地改变。在心理上观察到的平行于取向倾斜后效应的调谐中的这种可逆的生理变化。在风车中心或风车中心附近的神经元在通过定向刺激进行适应后显示出取向偏好的明显变化，而在同向域中的神经元则显示出最小的变化。在视觉注视的时间尺度上，机敏的猴子V1中的神经元在经过短暂的适应性定向刺激后，也表现出短期定向可塑性。与正交于神经元的首选方向的刺激相适应不会改变首选方向，但会增强方向调整。因此，自然视觉期间发生的相异图像斑块的连续固定与快速的皮质可塑性机制相结合，实际上改善了方向辨别力。最后，自然视觉涉及根据视觉世界的内部模型判断下一个目标。在行为猴子中进行的实验可以在一组试验中获得有关未来刺激位置的信息，而在另一组试验中却无法获得，这表明V1神经元发出内部表示信号。这种基于统计学习的贝叶斯更新响应对于更高级别的视觉，推论视觉世界的结构以及调节眼球运动至关重要。

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