Morton Neal W, Polyn Sean M
The University of Texas at Austin, Center for Learning & Memory, 1 University Station Stop C7000, Austin, TX 78712-0805, United States.
Vanderbilt University, Department of Psychology, PMB 407817, 2301 Vanderbilt Place, Nashville, TN 37240-7817, United States.
Neuroimage. 2017 Feb 15;147:692-702. doi: 10.1016/j.neuroimage.2016.12.049. Epub 2016 Dec 21.
While much research has focused on understanding how individual stimuli are encoded in episodic memory, less is known about how a series of events is bound into a coherent episode. Cognitive models of episodic memory propose that information about presented stimuli is integrated into a composite representation reflecting one's past experience, allowing events separated in time to become associated. Recent evidence suggests that neural oscillatory activity may be critically involved in this process. To examine how oscillatory activity contributes to binding of information across events, we measured scalp EEG as participants studied categorized lists of people, places, and objects. We assessed their memory for the lists using free recall, allowing us to characterize the temporal and semantic organization of the studied items in memory. Using pattern classification, we identified EEG activity during encoding at a range of frequencies and scalp locations that was sensitive to the category of presented stimuli. In the beta band (16-25Hz) at right posterior electrodes, we observed activity that was also sensitive to the category of recently presented stimuli. This neural activity showed two characteristics consistent with a representation of the recent past: It became stronger when multiple items from the same category were presented in succession, and it contained a fading trace of the previous category after a category shift. When items were separated by an inter-item distraction task, this integrative beta-band activity was disrupted. Distraction also led to decreased semantic organization of the studied materials without affecting their temporal organization; this suggests that distraction disrupts the integration of semantic information over time, preventing encoding of items in terms of the semantic context of earlier items. Our results provide evidence that beta-band activity is involved in maintaining information about recent events, allowing construction of a coherent representation of a temporally extended episode in memory.
虽然许多研究都集中在理解单个刺激是如何在情景记忆中编码的，但对于一系列事件是如何被整合为一个连贯的情节却知之甚少。情景记忆的认知模型提出，关于所呈现刺激的信息被整合到一个反映个人过去经历的复合表征中，使得在时间上分开的事件能够建立联系。最近的证据表明，神经振荡活动可能在这个过程中起着关键作用。为了研究振荡活动如何促进跨事件的信息整合，我们在参与者学习按类别列出的人物、地点和物体清单时测量了头皮脑电图。我们通过自由回忆评估他们对清单的记忆，这使我们能够描述记忆中所学习项目的时间和语义组织。使用模式分类，我们在一系列频率和头皮位置上识别出编码过程中对所呈现刺激类别敏感的脑电图活动。在右后电极的β波段（16 - 25Hz），我们观察到的活动也对最近呈现刺激的类别敏感。这种神经活动表现出与近期过去表征一致的两个特征：当同一类别的多个项目连续呈现时，它会增强，并且在类别转换后包含前一个类别的逐渐消失的痕迹。当项目被项目间分心任务隔开时，这种整合性的β波段活动会被破坏。分心还导致所学习材料的语义组织减少，而不影响其时间组织；这表明分心会随着时间的推移破坏语义信息的整合，阻止根据早期项目的语义背景对项目进行编码。我们的结果提供了证据，表明β波段活动参与维持关于近期事件的信息，从而在记忆中构建一个时间上扩展的情节的连贯表征。
