Trends in Cognitive Sciences
ReviewCognitive and neural mechanisms of emotional memory
Section snippets
Encoding versus post-encoding effects
Fig. 1 illustrates the time course of processes that are associated with experiencing an emotionally arousing event. Encoding processes create the initial memory representation. After the event, post-encoding processes continue to influence the memory representation. The most important of these post-encoding processes is consolidation, a process by which new memories become more permanent and resistant to loss. The consolidation process is widely thought to require an extended period to
Neuroimaging studies
Neuroimaging studies of explicit emotional memory have attempted to identify key regions that are preferentially involved in memory for emotional stimuli. Encoding studies have characterized brain regions in which increased activity during encoding successfully predicts later memory for emotional stimuli. Retrieval studies have characterized areas that are preferentially active during the retrieval of emotional memories. The role of the amygdala has been of particular interest in these studies.
Retrieval of emotional memories
Turning to retrieval, emotional memory retrieval has been examined by assessing brain activity with PET during retrieval of emotional personal autobiographical memories and during the retrieval of experimenter-created memories for emotional picture stimuli. Retrieval of traumatic versus neutral personal memories by individuals with post-traumatic stress disorder activates limbic areas primarily in the right hemisphere, including the amygdala, anterior cingulate, and insular and temporal
Neuropsychological studies
Neuropsychological studies provide important converging evidence to support the findings of the neuroimaging studies, by showing that the areas identified by imaging are crucial for emotional memory, rather than simply showing correlated activity. Based on animal studies, bilateral amygdala lesions should abolish the enhancing effect of emotion on explicit memory.
An early study examined emotional memory in two individuals with bilateral calcification lesions of the amygdalae, which resulted
Encoding versus consolidation effects
These findings agree well with the model developed by McGaugh 4, 6, based on earlier animal studies in which the amygdala modulates long-term memory consolidation. However, this model cannot completely account for all the data obtained from studies in humans. For example, a crucial aspect of the concept of consolidation is that it takes place gradually over an extended period 6, 36. However, the proposed timescale for consolidation has varied widely across studies, from as short as 30 min to
Conclusions
Each of the key concepts from the earlier animal studies has received considerable support from these neuroimaging, neuropsychological, drug and neural stimulation studies in humans (see also Box 2). The crucial role of the amygdala as modulator of explicit emotional memory has been supported by the observed effects of bilateral amygdala lesions and correlations between amygdala activity at encoding and later emotional memory enhancement. An important issue for future research will be to relate
Questions for future research
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What are the similarities and differences between the cognitive and neural mechanisms that mediate the effects of positive and negative emotion on explicit memory?
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What is the relationship between conscious (explicit) and non-conscious (implicit) aspects of emotional memory?
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What neural systems beyond the amygdala are engaged by explicit emotional memory and how does the amygdala interact with them?
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Is the amygdala necessary for the actual retrieval of emotional explicit memories, or is the
Acknowledgements
The author's research was supported by a James S. McDonnell foundation grant no. 97-24 and the Emory University Research Committee.
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