@article {1682, title = {Mean signal and response time influences on multivoxel signals of contextual retrieval in the medial temporal lobe.}, journal = {Brain Behav}, volume = {5}, year = {2015}, month = {2015 Feb}, pages = {e00302}, abstract = {

INTRODUCTION: The medial temporal lobe supports integrating the "what," "where," and "when" of an experience into a unified memory. However, it remains unclear how representations of these contextual features are neurally encoded and distributed across medial temporal lobe subregions.

METHODS: This study conducted functional magnetic resonance imaging of the medial temporal lobe, while participants retrieved pair, spatial, and temporal source memories. Multivoxel classifiers were trained to distinguish between retrieval conditions before and after correction for mean signal and response times, to more thoroughly characterize the multivoxel signal associated with memory context.

RESULTS: Activity in perirhinal and parahippocampal cortex dissociated between memory for associated items and memory for their spatiotemporal context, and hippocampal activity was linked to memory for spatial context. However, perirhinal and hippocampal classifiers were, respectively, driven by effects of mean signal amplitude and task difficulty, whereas the parahippocampal classifier survived correction for these effects.

CONCLUSION: These findings demonstrate dissociable coding mechanisms for episodic memory context across the medial temporal lobe, and further highlight a critical distinction between multivoxel representations driven by spatially distributed activity patterns, and those driven by the regional signal.

}, keywords = {Adult, Brain Mapping, Female, Humans, Magnetic Resonance Imaging, Male, Memory, Photic Stimulation, Temporal Lobe, Young Adult}, issn = {2162-3279}, doi = {10.1002/brb3.302}, author = {Reas, Emilie T and Brewer, James B} } @article {1675, title = {Using single-trial EEG to predict and analyze subsequent memory.}, journal = {Neuroimage}, volume = {84}, year = {2014}, month = {2014 Jan 01}, pages = {712-23}, abstract = {

We show that it is possible to successfully predict subsequent memory performance based on single-trial EEG activity before and during item presentation in the study phase. Two-class classification was conducted to predict subsequently remembered vs. forgotten trials based on subjects{\textquoteright} responses in the recognition phase. The overall accuracy across 18 subjects was 59.6\% by combining pre- and during-stimulus information. The single-trial classification analysis provides a dimensionality reduction method to project the high-dimensional EEG data onto a discriminative space. These projections revealed novel findings in the pre- and during-stimulus periods related to levels of encoding. It was observed that the pre-stimulus information (specifically oscillatory activity between 25 and 35Hz) -300 to 0ms before stimulus presentation and during-stimulus alpha (7-12Hz) information between 1000 and 1400ms after stimulus onset distinguished between recollection and familiarity while the during-stimulus alpha information and temporal information between 400 and 800ms after stimulus onset mapped these two states to similar values.

}, keywords = {Adolescent, Adult, Brain, Electroencephalography, Humans, Male, Memory, Young Adult}, issn = {1095-9572}, doi = {10.1016/j.neuroimage.2013.09.028}, author = {Noh, Eunho and Herzmann, Grit and Curran, Tim and de Sa, Virginia R} } @article {183, title = {Selection of distinct populations of dentate granule cells in response to inputs as a mechanism for pattern separation in mice.}, journal = {Elife}, volume = {2}, year = {2013}, month = {2013}, pages = {e00312}, abstract = {

The hippocampus is critical for episodic memory and computational studies have predicted specific functions for each hippocampal subregion. Particularly, the dentate gyrus (DG) is hypothesized to perform pattern separation by forming distinct representations of similar inputs. How pattern separation is achieved by the DG remains largely unclear. By examining neuronal activities at a population level, we revealed that, unlike CA1 neuron populations, dentate granule cell (DGC) ensembles activated by learning were not preferentially reactivated by memory recall. Moreover, when mice encountered an environment to which they had not been previously exposed, a novel DGC population-rather than the previously activated DGC ensembles that responded to past events-was selected to represent the new environmental inputs. This selection of a novel responsive DGC population could be triggered by small changes in environmental inputs. Therefore, selecting distinct DGC populations to represent similar but not identical inputs is a mechanism for pattern separation. DOI:http://dx.doi.org/10.7554/eLife.00312.001.

}, keywords = {Animals, Behavior, Animal, Brain Mapping, CA1 Region, Hippocampal, Conditioning (Psychology), Cues, Dentate Gyrus, Environment, Fear, Gene Expression Regulation, Genes, Reporter, Memory, Memory, Episodic, Mental Recall, Mice, Inbred BALB C, Mice, Inbred C57BL, Mice, Transgenic, Neural Pathways, Neurons, Pattern Recognition, Physiological, Time Factors}, issn = {2050-084X}, doi = {10.7554/eLife.00312}, author = {Deng, Wei and Mayford, Mark and Gage, Fred H} } @article {207, title = {Hippocampal signals for strong memory when associative memory is available and when it is not.}, journal = {Hippocampus}, volume = {21}, year = {2011}, month = {2011 Jan}, pages = {9-21}, abstract = {

The paired-associate task has been used with functional magnetic resonance imaging (fMRI) in studies that assessed the role of the medial temporal lobe (MTL) subserving recollection and familiarity.Some researchers have interpreted their results to mean that the hippocampus selectively subserves recollection and not familiarity[cf., Eichenbaum et al., (2007) Annu Rev Neurosci 30:123{\textendash}152]. Yet many of these results confound recollection and familiarity with strong and weak memories, and it is not clear whether the conclusions represent differences between memory processes or memory strength. In the current study, participants were scanned with fMRI during retrieval in a paired-associate task, and a new approach separated the analysis of memory strength from the analysis of memory processes. The data were sorted by confidence level in an old/new task, and the high-confidence responses were compared in categories when associative memory was highly accurate and when it was not available. The results show that high-confidence memory produced increased activity in the hippocampus,relative to the level for forgotten pairs, both when associative memory was available and when it was not. Two interpretations are discussed for the behavioral results for when associative memory was not available: one account based on familiarity and the other account based on noncriterial recollection. The conclusion is that recognition of the word-pairs was based on familiarity when associative memory was not available. Together with the fMRI results that activity in two regions associated with cognitive control (left ventrolateral prefrontal cortex and left inferior parietal lobule) was greater when responses were based on associative memory than when based on familiarity, the findings suggest that the hippocampus supports strong memory and that cortical regions make an additional contribution to recollection.

}, keywords = {Brain Mapping, Female, Hippocampus, Humans, Image Processing, Computer-Assisted, Magnetic Resonance Imaging, Male, Memory}, issn = {1098-1063}, doi = {10.1002/hipo.20716}, author = {Wais, Peter E} } @article {182, title = {New neurons and new memories: how does adult hippocampal neurogenesis affect learning and memory?}, journal = {Nat Rev Neurosci}, volume = {11}, year = {2010}, month = {2010 May}, pages = {339-50}, abstract = {

The integration of adult-born neurons into the circuitry of the adult hippocampus suggests an important role for adult hippocampal neurogenesis in learning and memory, but its specific function in these processes has remained elusive. In this article, we summarize recent progress in this area, including advances based on behavioural studies and insights provided by computational modelling. Increasingly, evidence suggests that newborn neurons might be involved in hippocampal functions that are particularly dependent on the dentate gyrus, such as pattern separation. Furthermore, newborn neurons at different maturation stages may make distinct contributions to learning and memory. In particular, computational studies suggest that, before newborn neurons are fully mature, they might function as a pattern integrator by introducing a degree of similarity to the encoding of events that occur closely in time.

}, keywords = {Adult Stem Cells, Animals, Hippocampus, Humans, Learning, Memory, Models, Neurological, Neurogenesis, Neurons}, issn = {1471-0048}, doi = {10.1038/nrn2822}, author = {Deng, Wei and Aimone, James B and Gage, Fred H} } @article {177, title = {Sustained dorsal hippocampal activity is not obligatory for either the maintenance or retrieval of long-term spatial memory.}, journal = {Hippocampus}, volume = {20}, year = {2010}, month = {2010 Dec}, pages = {1366-75}, abstract = {

Memories are initially stored in a labile state and are subject to modification by a variety of treatments, including disruption of hippocampal function. We infused a sodium channel blocker (or CNQX) to inactivate the rat dorsal hippocampus reversibly for 1 week following training on a task of spatial memory (the water maze). Previous work with conventional lesions has established that the dorsal hippocampus is essential for both the acquisition and expression of memory in this task. The question in the present study was whether chronic disruption of neuronal activity in the dorsal hippocampus after training would abolish memory or whether memory would survive extended disruption of hippocampal activity. As expected from earlier work, we found that performance was impaired during the infusion period. The critical test occurred 1 week after the lesion was reversed. We found that retention of the water maze recovered to control levels. Accordingly, sustained hippocampal activity following training is not obligatory for either the maintenance of long-term spatial memory or its subsequent retrieval.

}, keywords = {6-Cyano-7-nitroquinoxaline-2,3-dione, Animals, Excitatory Amino Acid Antagonists, Hippocampus, Male, Maze Learning, Memory, Rats, Rats, Long-Evans, Space Perception, Spatial Behavior}, issn = {1098-1063}, doi = {10.1002/hipo.20722}, author = {Broadbent, Nicola J and Squire, Larry R and Clark, Robert E} } @article {175, title = {Computational influence of adult neurogenesis on memory encoding.}, journal = {Neuron}, volume = {61}, year = {2009}, month = {2009 Jan 29}, pages = {187-202}, abstract = {

Adult neurogenesis in the hippocampus leads to the incorporation of thousands of new granule cells into the dentate gyrus every month, but its function remains unclear. Here, we present computational evidence that indicates that adult neurogenesis may make three separate but related contributions to memory formation. First, immature neurons introduce a degree of similarity to memories learned at the same time, a process we refer to as pattern integration. Second, the extended maturation and change in excitability of these neurons make this added similarity a time-dependent effect, supporting the possibility that temporal information is included in new hippocampal memories. Finally, our model suggests that the experience-dependent addition of neurons results in a dentate gyrus network well suited for encoding new memories in familiar contexts while treating novel contexts differently. Taken together, these results indicate that new granule cells may affect hippocampal function in several unique and previously unpredicted ways.

}, keywords = {Age Factors, Algorithms, Animals, Cell Proliferation, Computer Simulation, Dentate Gyrus, Humans, Memory, Nerve Net, Neural Pathways, Neurogenesis, Neuronal Plasticity, Neurons, Stem Cells, Synapses, Time Perception}, issn = {1097-4199}, doi = {10.1016/j.neuron.2008.11.026}, author = {Aimone, James B and Wiles, Janet and Gage, Fred H} }