Pinpointing the neural signatures of single-exposure visual recognition memory

Memories of the images that we have seen are thought to be reflected in the reduction of neural responses in high-level visual areas such as inferotemporal (IT) cortex, a phenomenon known as repetition suppression (RS). We challenged this hypothesis with a task that required rhesus monkeys to report whether images were novel or repeated while ignoring variations in contrast, a stimulus attribute that is also known to modulate the overall IT response. The monkeys’ behavior was largely contrast-invariant, contrary to the predictions of an RS-inspired decoder, which could not distinguish responses to images that are repeated from those that are of lower contrast. However, the monkeys’ behavioral patterns were well-predicted by a linearly decodable variant in which the total spike count was corrected for contrast modulation. These results suggest that the IT neural activity pattern that best aligns with single-exposure visual recognition memory behavior is not RS but rather “sensory referenced suppression (SRS)”: reductions in IT population response magnitude, corrected for sensory modulation.

学界普遍认为，我们对所见图像的记忆，可通过高级视觉脑区（如颞下（inferotemporal, IT）皮层）的神经响应衰减得以体现，该现象被称为重复抑制（repetition suppression, RS）。我们通过一项任务对该假说提出挑战：该任务要求恒河猴判断图像是新颖的还是重复呈现的，同时需忽略对比度的变化——对比度作为一种刺激属性，已知可调节颞下皮层的整体响应。恒河猴的行为表现基本不受对比度影响，这与基于重复抑制的解码器的预测结果相悖：这类解码器无法区分对重复呈现图像的响应与对比度更低的图像的响应。然而，一种对总脉冲数进行对比度调制校正的线性可解码模型变体，却能够精准预测恒河猴的行为模式。上述结果表明，与单次暴露视觉识别记忆行为匹配度最高的颞下神经活动模式，并非重复抑制，而是“感觉参照抑制（sensory referenced suppression, SRS）”：即经过感官调制校正后的颞下群体响应幅度衰减。