Dataset Information

Activity of human hippocampal and amygdala neurons during retrieval of declarative memories.

ABSTRACT: Episodic memories allow us to remember not only that we have seen an item before but also where and when we have seen it (context). Sometimes, we can confidently report that we have seen something (familiarity) but cannot recollect where or when it was seen. Thus, the two components of episodic recall, familiarity and recollection, can be behaviorally dissociated. It is not clear, however, whether these two components of memory are represented separately by distinct brain structures or different populations of neurons in a single anatomical structure. Here, we report that the spiking activity of single neurons in the human hippocampus and amygdala [the medial temporal lobe (MTL)] contain information about both components of memory. We analyzed a class of neurons that changed its firing rate to the second presentation of a previously novel stimulus. We found that the neuronal activity evoked by the presentation of a familiar stimulus (during retrieval) distinguishes stimuli that will be successfully recollected from stimuli that will not be recollected. Importantly, the ability to predict whether a stimulus is familiar is not influenced by whether the stimulus will later be recollected. We thus conclude that human MTL neurons contain information about both components of memory. These data support a continuous strength of memory model of MTL function: the stronger the neuronal response, the better the memory.

SUBMITTER: Rutishauser U

PROVIDER: S-EPMC2224211 | biostudies-literature | 2008 Jan

REPOSITORIES: biostudies-literature

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Activity of human hippocampal and amygdala neurons during retrieval of declarative memories.

Rutishauser Ueli U Schuman Erin M EM Mamelak Adam N AN

Proceedings of the National Academy of Sciences of the United States of America 20071227 1

Episodic memories allow us to remember not only that we have seen an item before but also where and when we have seen it (context). Sometimes, we can confidently report that we have seen something (familiarity) but cannot recollect where or when it was seen. Thus, the two components of episodic recall, familiarity and recollection, can be behaviorally dissociated. It is not clear, however, whether these two components of memory are represented separately by distinct brain structures or different ...[more]

PMID: 18162554

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Project description:Electrophysiological studies in animals have shown coordinated reactivation of neuronal ensembles during a restricted time period of behavioral inactivity that immediately followed active encoding. In the present study we directly investigated off-line processing of associative memory formation in the human brain. Subjects' regional cerebral blood flow (rCBF) as a surrogate marker of neural activity during rest was measured by MR-based perfusion imaging in a sample of 14 healthy male subjects prior to (Pre2) and after (Post) extensive learning of 24 face-name associations within a selective reminding task (SR). Results demonstrated significant Post-Pre2 rCBF increases in hippocampal and temporal lobe regions, while in a control comparison of two perfusion scans with no learning task in-between (Pre2-Pre1) no differences in rCBF emerged. Post perfusion scanning was followed by a surprise cued associative recall task from which two types of correctly retrieved names were obtained: older names already correctly retrieved at least once during one of the SR blocks, and recent names acquired during the last SR block immediately prior to the Post scan. In the anterior hippocampus individual perfusion increases were correlated with both correct retrievals of older and recent names. By contrast, older but not recently learned names showed a significant correlation with perfusion increases in the left lateral temporal cortex known to be associated with long-term memory. Recent, but not older names were correlated with dopaminergic midbrain structures reported to contribute to the persistence of memory traces for novel information. Although the direct investigation of off-line memory processing did not permit concomitant experimental control, neither intentional rehearsal, nor substantial variations in subjects' states of alertness appear to contribute to present results. We suggest that the observed rCBF increases might reflect processes that possibly contribute to the long-term persistence of memory traces.

Dataset Information

Activity of human hippocampal and amygdala neurons during retrieval of declarative memories.

Publications

Activity of human hippocampal and amygdala neurons during retrieval of declarative memories.

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