Brief stimuli cast a persistent long-term trace in visual cortex

Visual processing is strongly influenced by the recent stimulus history – a phenomenon termed adaptation. Prominent theories cast adaptation as a consequence of optimized encoding of visual information, by exploiting the temporal statistics of the world. However, this would require the visual system to track the history of individual briefly experienced events, within a stream of visual input, to build up statistical representations over longer timescales. Here, using an openly available dataset from the Allen Brain Observatory, we show that neurons in the early visual cortex of the mouse indeed maintain long-term traces of individual past stimuli that persist despite the presentation of several intervening stimuli, leading to long-term and stimulus-specific adaptation over dozens of seconds. Long-term adaptation was selectively expressed in cortical, but not in thalamic neurons, which only showed short-term adaptation. Early visual cortex thus maintains concurrent stimulus-specific memory traces of past input, enabling the visual system to build up a statistical representation of the world to optimize the encoding of new information in a changing environment.

视觉加工过程会显著受到近期刺激历史的影响——这一现象被称为适应（adaptation）。主流理论将适应视作视觉信息优化编码的结果，即通过利用外界环境的时间统计特性实现编码优化。然而，该理论要求视觉系统能够在连续的视觉输入流中，追踪单次短暂呈现刺激的历史，进而在更长的时间尺度上构建统计表征。本研究借助来自艾伦脑科学观测数据集（Allen Brain Observatory）的公开可用数据集，证实小鼠早期视觉皮层的神经元确实能够保留单次过往刺激的长期痕迹：即便其间穿插了多个其他刺激，该痕迹仍可持续存在，最终在数十秒的时间尺度上引发长期且具有刺激特异性的适应效应。研究发现，长期适应仅选择性地在皮层神经元中表达，丘脑神经元仅表现出短期适应，未出现长期适应现象。由此可见，早期视觉皮层会同时保留过往输入的刺激特异性记忆痕迹，使得视觉系统能够构建外界环境的统计表征，从而在动态变化的环境中优化对新信息的编码。