Trends in Cognitive Sciences
ReviewObserving the transformation of experience into memory
Section snippets
The first steps to remembering: witnessing the creation of memories
Episodic encoding refers to the initial information processing steps whereby a memory trace is created such that it can subsequently support the conscious recollection of one's past [1]. Encoding depends on at least two components:
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The initial component mediates the transformation of sensory input into internal representations that are interpreted or comprehended. This often entails the retrieval of associated knowledge relevant to current goals.
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The second component binds the internal
Encoding circuits: evidence from stimulus effects
The cerebral cortex consists of multiple processing modules that represent and perform computations on specific stimulus dimensions or features, such as visual attributes, spatial configuration, and domains of meaning. High-level outputs from neocortical processing modules are directed to the medial aspect of the temporal lobe (MTL), which binds representations together in the service of episodic memory formation. Different combinations of neocortical circuits can thus potentially interact with
Processing goals influence encoding
The configuration of neocortical modules that mediate encoding varies not only with the nature of the stimulus but also with how attention is allocated to different stimulus features and types of processing. A central theoretical focus in memory research has concerned the influence of goal-directed attentional orientation on encoding, as can be manipulated by instructions to process stimuli for meaning, phonology, or structural form 28, 29. Initial PET and fMRI studies of encoding using blocked
Fractionating episodic memory
The experience of an episode does not yield a single, undifferentiated memory trace. Rather, multiple forms of learning simultaneously occur during event processing. Subsequently, those various traces can support qualitatively different memory phenomena. For instance, behavioral and neuropsychological evidence suggests that memory for the prior occurrence of a stimulus is distinct from memory for a conglomeration of specific details about that prior experience. In the latter case, the retrieval
Medial temporal contributions to encoding
Neocortical and medial temporal regions make different contributions to episodic memory. Even with a severe amnesia, the active representation of the multidimensional features of moment-to-moment experiences can still be supported by neocortical mechanisms. By contrast, storing neocortical memory fragments as coherent episodic representations is characteristically problematic in amnesia. The hippocampus and associated MTL structures (perirhinal, entorhinal and parahippocampal cortices) might
Reverse engineering cognitive architecture
To what extent can episodic encoding be influenced by working memory maintenance processes? A prevalent view is that ‘ “mindless” rote rehearsal per se is insufficient to create durable memories’ ([78] p. 23). This view is based on the lack of a correlation between rehearsal duration and later recall 79, 80, and the robust effects of levels-of-processing on episodic memory. However, behavioral evidence that rote rehearsal can facilitate subsequent recognition 81, 82, 83 has been substantiated
Conclusion
The ability to remember an episode is a function of multiple processes, some of which are engaged at encoding, some at retrieval, some in-between, and some emerging as an outcome of how encoding and retrieval processes interrelate. Intermediate processes constituting additional encoding or consolidation may be particularly critical for the stability of episodic memories over time 92, 93, 94. One limitation of current implementations of the subsequent memory paradigm is that such intermediate
Questions for future research
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Are the neural computations correlated with subsequent memory necessary for effective memory formation? Can they be selectively disrupted via transcranial magnetic stimulation such that forgetting results?
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How do global changes in cognitive set or attentional state, which remain undetected by typical subsequent memory analyses conducted at the item-level, impact encoding? How do the effects of global state interact with event-related encoding processes?
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How do prefrontal and posterior neocortical
Acknowledgements
This article represents a collaborative effort based on equal contributions from the two authors. We thank R. Poldrack for insightful comments on an earlier draft, and gratefully acknowledge research support from NIDCD (DC04466), NIMH (MH60941), NINDS (NS34639), Ellison Medical Foundation, McKnight Endowment Fund for Neuroscience, and P. Newton.
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