علوم اعصاب شناختی کدگذاری حافظه اپیزودیک

This paper presents a cognitive neuroscientific perspective on how human episodic memories are formed. Convergent evidence from multiple brain imaging studies using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) suggests a role for frontal cortex in episodic memory encoding. Activity levels within frontal cortex can predict episodic memory encoding across a wide range of behavioral manipulations known to influence memory performance, such as those present during levels of processing and divided attention manipulations. Activity levels within specific frontal and medial temporal regions can even predict, on an item by item basis, whether an episodic memory is likely to form. Furthermore, separate frontal regions appear to participate in supplying code-specific information, including distinct regions which process semantic attributes of verbal information as well as right-lateralized regions which process nonverbal information. We hypothesize that activity within these multiple frontal regions provides a functional influence (input) to medical temporal regions that bind the information together into a lasting episodic memory trace.

The question addressed in this paper is simple: why do certain events and experiences form episodic memories? This question can be answered at different levels of description. At one level, theories from cognitive psychology provide an account of how certain forms of processing facilitate episodic memory formation, outlining the conditions necessary to promote these forms of processing and the many variables that may influence retrieval of episodic memories after they have formed. At another level, evidence from neuroscience provides information about the neural structures that support encoding, and characterizes the operations carried out by these neural structures. The view of encoding presented here reflects a cognitive neuroscience approach that relates these two levels of description. The aim is to understand how encoding and its behavioral manifestations arise from the workings of underlying neural structures. What follows is a review of recent results from brain imaging studies that suggests a cognitive neuroscience theory of how episodic memories form and why some experiences are more likely than others to establish a lasting memory trace. While the theory is incomplete, there is good evidence supporting the notion that certain types of encoding processes may onto neural activity within specific brain regions, and that evidence from neuroscience can inform and constrain studies of behavior and vice versa. Although several brain regions are likely to be involved in episodic memory formation, in this paper particular focus is placed on (1) the role of the frontal cortex in episodic memory encoding, and (2) how frontal regions may interact with medical temporal regions that play a well-established role in episodic (and semantic) memory formation. The main conclusion drawn is that for an episodic memory to form an event must encourage elaboration of information within specific frontal regions that provide a critical input to medical temporal cortex. Components of these ideas have been presented previously (e.g., for a highly overlapping explication see Buckner et al., 1999 and Buckner, 1999).

In conclusion the findings and interpretations presented here expand on general ideas about the importance of frontal and medial temporal regions in memory. We draw from recent functional brain imaging studies of memory encoding to suggest that the frontal cortex provides an essential input to medial temporal regions during the formation of an episodic memory. Importantly, the specific regions of frontal cortex that are active appear to be dependent upon current task goals and the on-line processing that results. Consequently, different regions of frontal cortex are active when verbal and nonverbal stimuli are presented, and when different types of verbal processing (e.g., phonological versus semantic) are encouraged. In each case, however, the processing is hypothesized to provide a critical input to the medial temporal lobes, contributing to the lasting formation of an episodic memory. Of course the ideas presented here are simply meant as heuristics which highlight a small but important subset of the functional anatomy underlying episodic memory formation. Frontal cortex activity and interactions with medial temporal lobe structures are undoubtedly not the only determinants of memory formation, but their presence appears to be key element of episodic encoding and worthy of further study.