Rotman Research Institute at Baycrest, 3560 Bathurst Street, Toronto, Ontario, M6A 2E1, Canada.
Rotman Research Institute at Baycrest, 3560 Bathurst Street, Toronto, Ontario, M6A 2E1, Canada; Department of Psychology, York University, Faculty of Health, Behavioural Sciences Building, 4700 Keele Street, Toronto, Ontario, M3J 1P3, Canada.
Neuropsychologia. 2020 May;142:107436. doi: 10.1016/j.neuropsychologia.2020.107436. Epub 2020 Mar 16.
As clear memories transport us back into the past, the brain also revives prior patterns of neural activity, a phenomenon known as neural reactivation. While growing evidence indicates a link between neural reactivation and typical variations in memory performance in healthy individuals, it is unclear how and to what extent reactivation is disrupted by a memory disorder. The current study characterizes neural reactivation in a case of amnesia using Multivoxel Pattern Analysis (MVPA). We tested NC, an individual with developmental amnesia linked to a diencephalic stroke, and 19 young adult controls on a functional magnetic resonance imaging (fMRI) task during which participants viewed and recalled short videos multiple times. An encoding classifier trained and tested to identify videos based on brain activity patterns elicited at perception revealed superior classification in NC. The enhanced consistency in stimulus representation we observed in NC at encoding was accompanied by an absence of multivariate repetition suppression, which occurred over repeated viewing in the controls. Another recall classifier trained and tested to identify videos during mental replay indicated normal levels of classification in NC, despite his poor memory for stimulus content. However, a cross-condition classifier trained on perception trials and tested on mental replay trials-a strict test of reactivation-revealed significantly poorer classification in NC. Thus, while NC's brain activity was consistent and stimulus-specific during mental replay, this specificity did not reflect the reactivation of patterns elicited at perception to the same extent as controls. Fittingly, we identified brain regions for which activity supported stimulus representation during mental replay to a greater extent in NC than in controls. This activity was not modeled on perception, suggesting that compensatory patterns of representation based on generic knowledge can support consistent mental constructs when memory is faulty. Our results reveal several ways in which amnesia impacts distributed patterns of stimulus representation during encoding and retrieval.
当清晰的记忆将我们带回到过去时，大脑也会重新激活先前的神经活动模式，这种现象被称为神经再激活。虽然越来越多的证据表明神经再激活与健康个体记忆表现的典型变化之间存在联系，但目前尚不清楚再激活是如何以及在多大程度上受到记忆障碍的干扰。本研究使用多体素模式分析 (MVPA) 来描述遗忘症患者的神经再激活。我们测试了 NC，一个与间脑中风有关的发育性遗忘症患者，以及 19 名年轻成年对照组，他们在功能磁共振成像 (fMRI) 任务中多次观看和回忆短视频。一个基于感知时引发的大脑活动模式来识别视频的编码分类器被训练和测试，结果表明 NC 的分类能力更好。我们观察到 NC 在编码时刺激表示的一致性增强，伴随着在对照组中多次观看时出现的多变量重复抑制的缺失。另一个在心理回放期间训练和测试以识别视频的回忆分类器表明 NC 的分类水平正常，尽管他对刺激内容的记忆很差。然而，一个在感知试验上训练并在心理回放试验上测试的跨条件分类器——这是对再激活的严格测试——表明 NC 的分类能力明显较差。因此，尽管 NC 的大脑活动在心理回放期间是一致的并且是特定于刺激的，但这种特异性并没有反映出与对照组相同程度的感知时引发的模式的再激活。恰当地说，我们确定了在 NC 中比在对照组中更能支持心理回放期间刺激表示的大脑区域。这种活动不是基于感知建模的，这表明基于通用知识的补偿表示模式可以在记忆出现故障时支持一致的心理结构。我们的研究结果揭示了遗忘症在编码和检索期间对刺激表示的分布式模式产生影响的几种方式。
