Memory integration: neural mechanisms and implications for behavior - PubMed (original) (raw)
Memory integration: neural mechanisms and implications for behavior
Margaret L Schlichting et al. Curr Opin Behav Sci. 2015 Feb.
Abstract
Everyday behaviors require a high degree of flexibility, in which prior knowledge is applied to inform behavior in new situations. Such flexibility is thought to be supported in part by memory integration, a process whereby related memories become interconnected in the brain through recruitment of overlapping neuronal populations. Recent advances in cognitive and behavioral neuroscience highlight the importance of a hippocampal-medial prefrontal circuit in memory integration. Emerging evidence suggests that abstracted representations in medial prefrontal cortex guide reactivation of related memories during new encoding events, thus promoting hippocampal integration of related experiences. Moreover, recent work indicates that integrated memories are called upon during novel situations to facilitate a host of behaviors, from spatial navigation to imagination.
Conflict of interest statement
Conflict of interest statement
Nothing declared.
Figures
Figure 1
Schematic depiction of memory integration. (a) Example overlapping events that might lead to integration and their associated neural codes. One day while walking in the park, you encounter a woman and her dog (initial experience, top panel). Connections are formed among a group of simultaneously activated neurons, coding the woman–dog association (blue network). A few days later, you encounter the same dog in town, this time with a man (overlapping event, bottom panel). The dog (overlapping element) triggers reactivation of your initial experience in the park (woman–dog association). Such reactivation enables connections to be formed among neural representations of the woman, dog, and man, linking the related events across time (overlapping blue and yellow networks). The resulting integrated memories are hypothesized to support novel judgments that require consideration of both events; here, for instance, you may infer a relationship between the woman and the man despite never having seen them together. (b) Top panel, depiction of a neural decoding approach quantifying the degree of memory reactivation during learning. The neural pattern evoked during the overlapping event is hypothesized to reflect reinstatement of the related — but not presently viewed — element (the woman). The fMRI signal is extracted for each voxel in a region of interest (here, ventral temporal cortex is used as an example). This information is then input into a neural decoder trained to recognize activation patterns associated with different kinds of stimuli (e.g., faces). On the basis of the weights for each voxel learned during training, the decoder outputs a value reflecting the degree to which the neural pattern reflects reactivation of the related versus unrelated content. These evidence scores can then be used as an index of reactivation. Bottom panel, evidence indicating that reactivation during encoding of overlapping events predicts later flexible inference (woman–man association), a behavioral index of memory integration. Adapted from Ref. [4••].
Figure 2
Locations and hypothesized functions of regions critical for memory integration in the human brain. Green, medial prefrontal cortex; purple, hippocampus. Here, we intentionally provide a broad definition of mPFC due to high variability in the precise location of effects reported across studies. For instance, we include anterior cingulate cortex, which has been implicated in memory integration [60] and the formation of memory models [20]. Inset, cross section through the hippocampus (purple) highlighting area CA1 (dark purple portion). Approximate hippocampal subfield boundaries are indicated with thin dashed lines. Location of cross section along hippocampal axis is indicated with a thick dashed line. mPFC, medial prefrontal cortex; CA1, Cornu ammonis field 1; DG/CA2,3, dentate gyrus and Cornu ammonis fields 2 and 3; SUB, subiculum.
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