AFNI: software for analysis and visualization of functional magnetic resonance neuroimages
Computers and Biomedical Research
A Parametric Manipulation of Factors Affecting Task-induced Deactivation in Functional Neuroimaging
Journal of Cognitive Neuroscience
The Influence of Working-Memory Demand and Subject Performance on Prefrontal Cortical Activity
Journal of Cognitive Neuroscience
Journal of Cognitive Neuroscience
Memory and working-with-memory: A component process model based on modules and central systems
Journal of Cognitive Neuroscience
Retrieval search and strength evoke dissociable brain activity during episodic memory recall
Journal of Cognitive Neuroscience
Negative bold response in the hippocampus during short-term spatial memory retrieval
Journal of Cognitive Neuroscience
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Hippocampal activity is modulated during episodic memory retrieval. Most consistently, a relative increase in activity during confident retrieval is observed. Dorsolateral prefrontal cortex (DLPFC) is also activated during retrieval, but may be more generally activated during cognitive-control processes. The "default network," regions activated during rest or internally focused tasks, includes the hippocampus, but not DLPFC. Therefore, DLPFC and the hippocampus should diverge during difficult tasks suppressing the default network. It is unclear, however, whether a difficult episodic memory retrieval task would suppress the default network due to difficulty or activate it due to internally directed attention. We hypothesized that a task requiring episodic retrieval followed by rumination on the retrieved item would increase DLPFC activity, but paradoxically reduce hippocampal activity due to concomitant suppression of the default network. In the present study, blocked and event-related fMRI were used to examine hippocampal activity during episodic memory recollection and postretrieval processing of paired associates. Subjects were asked to make living/nonliving judgments about items visually presented (classify) or items retrieved from memory (recall-classify). Active and passive baselines were used to differentiate task-related activity from default-network activity. During the "recall-classify" task, anterior hippocampal activity was selectively reduced relative to "classify" and baseline tasks, and this activity was inversely correlated with DLPFC. Reaction time was positively correlated with DLPFC activation and default-network/hippocampal suppression. The findings demonstrate that frontal and hippocampal activity are dissociated during difficult episodic retrieval tasks and reveal important considerations for interpreting hippocampal activity associated with successful episodic retrieval.