The Experts below are selected from a list of 5022 Experts worldwide ranked by ideXlab platform
Guillén Fernández - One of the best experts on this subject based on the ideXlab platform.
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The impact of sleep deprivation on declarative Memory.
Sleep Deprivation and Cognition, 2019Co-Authors: James N. Cousins, Guillén FernándezAbstract:Sleep plays a crucial role in Memory Stabilization and integration, yet many people obtain insufficient sleep. This review assesses what is known about the level of sleep deprivation that leads to impairments during encoding, consolidation and retrieval of declarative memories, and what can be determined about the underlying neurophysiological processes. Neuroimaging studies that deprived sleep after learning have provided some of the most compelling evidence for sleep's role in the long-term reorganization of memories in the brain (systems consolidation). However, the behavioral consequences of losing sleep after learning-shown by increased forgetting-appear to recover over time and are unaffected by more common forms of partial sleep restriction across several nights. The capacity to encode new memories is the most vulnerable to sleep loss, since long-term deficits have been observed after total and partial sleep deprivation, while retrieval mechanisms are relatively unaffected. The negative impact of sleep loss on Memory has been explored extensively after a night of total sleep deprivation, but further research is needed on the consequences of partial sleep loss over many days so that impairments may be generalized to more common forms of sleep loss.
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Cued reactivation during slow-wave sleep induces brain connectivity changes related to Memory Stabilization
Scientific Reports, 2018Co-Authors: Ruud Berkers, Atsuko Takashima, Matthias Ekman, Ken A. Paller, Eelco. V. Dongen, Markus Barth, Guillén FernándezAbstract:Memory reprocessing following acquisition enhances Memory consolidation. Specifically, neural activity during encoding is thought to be ‘replayed’ during subsequent slow-wave sleep. Such Memory replay is thought to contribute to the functional reorganization of neural Memory traces. In particular, Memory replay may facilitate the exchange of information across brain regions by inducing a reconfiguration of connectivity across the brain. Memory reactivation can be induced by external cues through a procedure known as “targeted Memory reactivation”. Here, we analysed data from a published study with auditory cues used to reactivate visual object-location memories during slow-wave sleep. We characterized effects of Memory reactivation on brain network connectivity using graph-theory. We found that cue presentation during slow-wave sleep increased global network integration of occipital cortex, a visual region that was also active during retrieval of object locations. Although cueing did not have an overall beneficial effect on the retention of cued versus uncued associations, individual differences in overnight Memory Stabilization were related to enhanced network integration of occipital cortex. Furthermore, occipital cortex displayed enhanced connectivity with mnemonic regions, namely the hippocampus, parahippocampal gyrus, thalamus and medial prefrontal cortex during cue sound presentation. Together, these results suggest a neural mechanism where cue-induced replay during sleep increases integration of task-relevant perceptual regions with mnemonic regions. This cross-regional integration may be instrumental for the consolidation and long-term storage of enduring memories.
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Cued reactivation during slow-wave sleep induces connectivity changes related to Memory Stabilization.
2017Co-Authors: Ruud Berkers, Atsuko Takashima, Matthias Ekman, Eelco V. Van Dongen, Marcus Barth, Ken A. Paller, Guillén FernándezAbstract:Memory reprocessing following acquisition enhances Memory consolidation. Specifically, neural activity during encoding is thought to be replayed during subsequent slow-wave sleep (SWS). This natural tendency of Memory replay can be induced by external cueing, known as targeted Memory reactivation. Here, we analyzed data from a published study (van Dongen, Takashima, et al. 2012), where auditory cues reactivated learned visual object-location memories during SWS. Memory replay during sleep presumably involves a shift in connectivity across the brain. Therefore, we characterized the effects of Memory reactivation on brain network connectivity using graph-theory. We found that cue presentation during SWS introduced increased network integration of the occipital cortex, a visual region that was also active during the object retrieval task. Importantly, enhanced network integration of the occipital cortex showed a behavioural benefit and predicted overnight Memory Stabilization. Furthermore, occipital cortex displayed enhanced connectivity with mnemonic regions, namely the hippocampus, parahippocampal gyrus, thalamus and medial prefrontal cortex during cue versus control sound presentation. Finally, network integration of early occipital cortex during cueing in SWS was related to increased activation of the bilateral parahippocampal gyrus, a region involved in coding for spatial associative information, at the post-sleep test. Together, these results support a neural mechanism where cue-induced replay during sleep promotes Memory consolidation by increased integration of task-relevant perceptual regions with mnemonic regions.
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Memory Stabilization with targeted reactivation during human slow-wave sleep
Proceedings of the National Academy of Sciences, 2012Co-Authors: Eelco V. Van Dongen, Atsuko Takashima, Ken A. Paller, Markus Barth, Jascha Zapp, Lothar R. Schad, Guillén FernándezAbstract:It is believed that neural representations of recent experiences become reactivated during sleep, and that this process serves to stabilize associated memories in long-term Memory. Here, we initiated this reactivation process for specific memories during slow-wave sleep. Participants studied 50 object-location associations with object-related sounds presented concurrently. For half of the associations, the related sounds were re-presented during subsequent slow-wave sleep while participants underwent functional MRI. Compared with control sounds, related sounds were associated with increased activation of right parahippocampal cortex. Postsleep Memory accuracy was positively correlated with sound-related activation during sleep in various brain regions, including the thalamus, bilateral medial temporal lobe, and cerebellum. In addition, postsleep Memory accuracy was also positively correlated with pre- to postsleep changes in parahippocampal-medial prefrontal connectivity during retrieval of reactivated associations. Our results suggest that the brain is differentially activated by studied and unstudied sounds during deep sleep and that the thalamus and medial temporal lobe are involved in establishing the mnemonic consequences of externally triggered reactivation of associative memories.
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Visual areas become less engaged in associative recall following Memory Stabilization.
NeuroImage, 2008Co-Authors: Ingrid L.c. Nieuwenhuis, Atsuko Takashima, Robert Oostenveld, Guillén Fernández, Ole JensenAbstract:Numerous studies have focused on changes in the activity in the hippocampus and higher association areas with consolidation and Memory Stabilization. Even though perceptual areas are engaged in Memory recall, little is known about how Memory Stabilization is reflected in those areas. Using magnetoencephalography (MEG) we investigated changes in visual areas with Memory Stabilization. Subjects were trained on associating a face to one of eight locations. The first set of associations ('stabilized') was learned in three sessions distributed over a week. The second set ('labile') was learned in one session just prior to the MEG measurement. In the recall session only the face was presented and subjects had to indicate the correct location using a joystick. The MEG data revealed robust gamma activity during recall, which started in early visual cortex and propagated to higher visual and parietal brain areas. The occipital gamma power was higher for the labile than the stabilized condition (time=0.65-0.9 s). Also the event-related field strength was higher during recall of labile than stabilized associations (time=0.59-1.5 s). We propose that recall of the spatial associations prior to Memory Stabilization involves a top-down process relying on reconstructing learned representations in visual areas. This process is reflected in gamma band activity consistent with the notion that neuronal synchronization in the gamma band is required for visual representations. More direct synaptic connections are formed with Memory Stabilization, thus decreasing the dependence on visual areas.
Ken A. Paller - One of the best experts on this subject based on the ideXlab platform.
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Targeted Memory Reactivation during Sleep Elicits Neural Signals Related to Learning Content.
The Journal of Neuroscience, 2019Co-Authors: Boyu Wang, Ken A. Paller, James W. Antony, Sarah Lurie, Paula P. Brooks, Kenneth A. NormanAbstract:Retrieval of learning-related neural activity patterns is thought to drive Memory Stabilization. However, finding reliable, noninvasive, content-specific indicators of Memory retrieval remains a central challenge. Here, we attempted to decode the content of retrieved memories in the EEG during sleep. During encoding, male and female human subjects learned to associate spatial locations of visual objects with left- or right-hand movements, and each object was accompanied by an inherently related sound. During subsequent slow-wave sleep within an afternoon nap, we presented half of the sound cues that were associated (during wake) with left- and right-hand movements before bringing subjects back for a final postnap test. We trained a classifier on sleep EEG data (focusing on lateralized EEG features that discriminated left- vs right-sided trials during wake) to predict learning content when we cued the memories during sleep. Discrimination performance was significantly above chance and predicted subsequent Memory, supporting the idea that retrieval leads to Memory Stabilization. Moreover, these lateralized signals increased with postcue sleep spindle power, demonstrating that retrieval has a strong relationship with spindles. These results show that lateralized activity related to individual memories can be decoded from sleep EEG, providing an effective indicator of offline retrieval.SIGNIFICANCE STATEMENT Memories are thought to be retrieved during sleep, leading to their long-term Stabilization. However, there has been relatively little work in humans linking neural measures of retrieval of individual memories during sleep to subsequent Memory performance. This work leverages the prominent electrophysiological signal triggered by lateralized movements to robustly demonstrate the retrieval of specific cued memories during sleep. Moreover, these signals predict subsequent Memory and are correlated with sleep spindles, neural oscillations that have previously been implicated in Memory Stabilization. Together, these findings link Memory retrieval to Stabilization and provide a powerful tool for investigating Memory in a wide range of learning contexts and human populations.
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Cued reactivation during slow-wave sleep induces brain connectivity changes related to Memory Stabilization
Scientific Reports, 2018Co-Authors: Ruud Berkers, Atsuko Takashima, Matthias Ekman, Ken A. Paller, Eelco. V. Dongen, Markus Barth, Guillén FernándezAbstract:Memory reprocessing following acquisition enhances Memory consolidation. Specifically, neural activity during encoding is thought to be ‘replayed’ during subsequent slow-wave sleep. Such Memory replay is thought to contribute to the functional reorganization of neural Memory traces. In particular, Memory replay may facilitate the exchange of information across brain regions by inducing a reconfiguration of connectivity across the brain. Memory reactivation can be induced by external cues through a procedure known as “targeted Memory reactivation”. Here, we analysed data from a published study with auditory cues used to reactivate visual object-location memories during slow-wave sleep. We characterized effects of Memory reactivation on brain network connectivity using graph-theory. We found that cue presentation during slow-wave sleep increased global network integration of occipital cortex, a visual region that was also active during retrieval of object locations. Although cueing did not have an overall beneficial effect on the retention of cued versus uncued associations, individual differences in overnight Memory Stabilization were related to enhanced network integration of occipital cortex. Furthermore, occipital cortex displayed enhanced connectivity with mnemonic regions, namely the hippocampus, parahippocampal gyrus, thalamus and medial prefrontal cortex during cue sound presentation. Together, these results suggest a neural mechanism where cue-induced replay during sleep increases integration of task-relevant perceptual regions with mnemonic regions. This cross-regional integration may be instrumental for the consolidation and long-term storage of enduring memories.
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Targeted Memory reactivation during sleep elicits neural signals related to learning content
2018Co-Authors: Boyu Wang, Ken A. Paller, James W. Antony, Sarah Lurie, Paula P. Brooks, Kenneth A. NormanAbstract:Reactivation of learning-related neural activity patterns is thought to drive Memory Stabilization. However, finding reliable, non-invasive, content-specific indicators of reactivation remains a central challenge. Here, we attempted to decode the content of reactivated memories in the electroencephalogram (EEG) during sleep. During encoding, human participants learned to associate spatial locations of visual objects with left- or right-hand movements, and each object was accompanied by an inherently related sound. During subsequent slow-wave sleep within an afternoon nap, we presented half of the sound cues that were associated (during wake) with left- and right-hand movements before bringing participants back for a final post-nap test. We trained a classifier on sleep EEG data (focusing on lateralized EEG features that discriminated left- vs. right-sided trials during wake) to predict learning content when we reactivated the memories during sleep. Discrimination performance was significantly above chance and predicted subsequent Memory, supporting the idea that reactivation leads to Memory Stabilization. Moreover, these lateralized signals increased with post-cue spindle power, demonstrating that reactivation has a strong relationship with spindles. These results show that lateralized activity related to individual memories can be decoded from sleep EEG, providing an effective indicator of offline reactivation.
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Cued reactivation during slow-wave sleep induces connectivity changes related to Memory Stabilization.
2017Co-Authors: Ruud Berkers, Atsuko Takashima, Matthias Ekman, Eelco V. Van Dongen, Marcus Barth, Ken A. Paller, Guillén FernándezAbstract:Memory reprocessing following acquisition enhances Memory consolidation. Specifically, neural activity during encoding is thought to be replayed during subsequent slow-wave sleep (SWS). This natural tendency of Memory replay can be induced by external cueing, known as targeted Memory reactivation. Here, we analyzed data from a published study (van Dongen, Takashima, et al. 2012), where auditory cues reactivated learned visual object-location memories during SWS. Memory replay during sleep presumably involves a shift in connectivity across the brain. Therefore, we characterized the effects of Memory reactivation on brain network connectivity using graph-theory. We found that cue presentation during SWS introduced increased network integration of the occipital cortex, a visual region that was also active during the object retrieval task. Importantly, enhanced network integration of the occipital cortex showed a behavioural benefit and predicted overnight Memory Stabilization. Furthermore, occipital cortex displayed enhanced connectivity with mnemonic regions, namely the hippocampus, parahippocampal gyrus, thalamus and medial prefrontal cortex during cue versus control sound presentation. Finally, network integration of early occipital cortex during cueing in SWS was related to increased activation of the bilateral parahippocampal gyrus, a region involved in coding for spatial associative information, at the post-sleep test. Together, these results support a neural mechanism where cue-induced replay during sleep promotes Memory consolidation by increased integration of task-relevant perceptual regions with mnemonic regions.
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Reinforcing rhythms in the sleeping brain with a computerized metronome.
Neuron, 2013Co-Authors: Delphine Oudiette, Giovanni Santostasi, Ken A. PallerAbstract:Sleep has many inherent benefits, including an important role in Memory consolidation. In this issue of Neuron, Ngo et al. (2013b) demonstrate that appropriately timed sounds delivered during sleep can invigorate electrophysiological oscillations conducive to Memory Stabilization.
Ajaya K Nayak - One of the best experts on this subject based on the ideXlab platform.
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magnetic antiskyrmions above room temperature in tetragonal heusler materials
Nature, 2017Co-Authors: Vivek Kumar, Peter Werner, Eckhard Pippel, Roshnee Sahoo, Françoise Damay, Claudia Felser, Ajaya K Nayak, Ulrich K Rosler, S S P ParkinAbstract:Antiskyrmions, in which the magnetization rotates both as a transverse helix and as a cycloid, are found in acentric tetragonal Heusler compounds over a wide range of temperatures. Skyrmions, topologically stable, vortex-like spin textures, are of great interest for the development of a new generation of magnetic devices, in which they could carry or store information while remaining robust against disturbances. So far, only two types of skyrmion have been observed experimentally, the Bloch skyrmion and the Neel skyrmion, but Stuart Parkin and colleagues have now observed another type to join the family: the antiskyrmion. These are observed in a type of magnetic material called a centric tetragonal Heusler compound, which has unusual crystal symmetry. An antiskyrmion lattice state appears when magnetic fields are applied along the tetragonal axis, over a wide temperature interval. Because antiskyrmions break the cylindrical symmetry and carry a quadrupolar moment, their properties may differ from those of Bloch and Neel skyrmions and so they offer new opportunities for control. Magnetic skyrmions are topologically stable, vortex-like objects surrounded by chiral boundaries that separate a region of reversed magnetization from the surrounding magnetized material1,2,3. They are closely related to nanoscopic chiral magnetic domain walls, which could be used as Memory and logic elements for conventional and neuromorphic computing applications that go beyond Moore’s law. Of particular interest is ‘racetrack Memory’, which is composed of vertical magnetic nanowires, each accommodating of the order of 100 domain walls, and that shows promise as a solid state, non-volatile Memory with exceptional capacity and performance4,5. Its performance is derived from the very high speeds (up to one kilometre per second) at which chiral domain walls can be moved with nanosecond current pulses in synthetic antiferromagnet racetracks. Because skyrmions are essentially composed of a pair of chiral domain walls closed in on themselves, but are, in principle, more stable to perturbations than the component domain walls themselves, they are attractive for use in spintronic applications, notably racetrack Memory. Stabilization of skyrmions has generally been achieved in systems with broken inversion symmetry, in which the asymmetric Dzyaloshinskii–Moriya interaction modifies the uniform magnetic state to a swirling state6,7. Depending on the crystal symmetry, two distinct types of skyrmions have been observed experimentally, namely, Bloch7,8 and Neel skyrmions9. Here we present the experimental manifestation of another type of skyrmion—the magnetic antiskyrmion—in acentric tetragonal Heusler compounds with D2d crystal symmetry. Antiskyrmions are characterized by boundary walls that have alternating Bloch and Neel type as one traces around the boundary. A spiral magnetic ground-state, which propagates in the tetragonal basal plane, is transformed into an antiskyrmion lattice state under magnetic fields applied along the tetragonal axis over a wide range of temperatures. Direct imaging by Lorentz transmission electron microscopy shows field-stabilized antiskyrmion lattices and isolated antiskyrmions from 100 kelvin to well beyond room temperature, and zero-field metastable antiskyrmions at low temperatures. These results enlarge the family of magnetic skyrmions and pave the way to the engineering of complex bespoke designed skyrmionic structures.
Ruud Berkers - One of the best experts on this subject based on the ideXlab platform.
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Cued reactivation during slow-wave sleep induces brain connectivity changes related to Memory Stabilization
Scientific Reports, 2018Co-Authors: Ruud Berkers, Atsuko Takashima, Matthias Ekman, Ken A. Paller, Eelco. V. Dongen, Markus Barth, Guillén FernándezAbstract:Memory reprocessing following acquisition enhances Memory consolidation. Specifically, neural activity during encoding is thought to be ‘replayed’ during subsequent slow-wave sleep. Such Memory replay is thought to contribute to the functional reorganization of neural Memory traces. In particular, Memory replay may facilitate the exchange of information across brain regions by inducing a reconfiguration of connectivity across the brain. Memory reactivation can be induced by external cues through a procedure known as “targeted Memory reactivation”. Here, we analysed data from a published study with auditory cues used to reactivate visual object-location memories during slow-wave sleep. We characterized effects of Memory reactivation on brain network connectivity using graph-theory. We found that cue presentation during slow-wave sleep increased global network integration of occipital cortex, a visual region that was also active during retrieval of object locations. Although cueing did not have an overall beneficial effect on the retention of cued versus uncued associations, individual differences in overnight Memory Stabilization were related to enhanced network integration of occipital cortex. Furthermore, occipital cortex displayed enhanced connectivity with mnemonic regions, namely the hippocampus, parahippocampal gyrus, thalamus and medial prefrontal cortex during cue sound presentation. Together, these results suggest a neural mechanism where cue-induced replay during sleep increases integration of task-relevant perceptual regions with mnemonic regions. This cross-regional integration may be instrumental for the consolidation and long-term storage of enduring memories.
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Cued reactivation during slow-wave sleep induces connectivity changes related to Memory Stabilization.
2017Co-Authors: Ruud Berkers, Atsuko Takashima, Matthias Ekman, Eelco V. Van Dongen, Marcus Barth, Ken A. Paller, Guillén FernándezAbstract:Memory reprocessing following acquisition enhances Memory consolidation. Specifically, neural activity during encoding is thought to be replayed during subsequent slow-wave sleep (SWS). This natural tendency of Memory replay can be induced by external cueing, known as targeted Memory reactivation. Here, we analyzed data from a published study (van Dongen, Takashima, et al. 2012), where auditory cues reactivated learned visual object-location memories during SWS. Memory replay during sleep presumably involves a shift in connectivity across the brain. Therefore, we characterized the effects of Memory reactivation on brain network connectivity using graph-theory. We found that cue presentation during SWS introduced increased network integration of the occipital cortex, a visual region that was also active during the object retrieval task. Importantly, enhanced network integration of the occipital cortex showed a behavioural benefit and predicted overnight Memory Stabilization. Furthermore, occipital cortex displayed enhanced connectivity with mnemonic regions, namely the hippocampus, parahippocampal gyrus, thalamus and medial prefrontal cortex during cue versus control sound presentation. Finally, network integration of early occipital cortex during cueing in SWS was related to increased activation of the bilateral parahippocampal gyrus, a region involved in coding for spatial associative information, at the post-sleep test. Together, these results support a neural mechanism where cue-induced replay during sleep promotes Memory consolidation by increased integration of task-relevant perceptual regions with mnemonic regions.
Atsuko Takashima - One of the best experts on this subject based on the ideXlab platform.
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Cued reactivation during slow-wave sleep induces brain connectivity changes related to Memory Stabilization
Scientific Reports, 2018Co-Authors: Ruud Berkers, Atsuko Takashima, Matthias Ekman, Ken A. Paller, Eelco. V. Dongen, Markus Barth, Guillén FernándezAbstract:Memory reprocessing following acquisition enhances Memory consolidation. Specifically, neural activity during encoding is thought to be ‘replayed’ during subsequent slow-wave sleep. Such Memory replay is thought to contribute to the functional reorganization of neural Memory traces. In particular, Memory replay may facilitate the exchange of information across brain regions by inducing a reconfiguration of connectivity across the brain. Memory reactivation can be induced by external cues through a procedure known as “targeted Memory reactivation”. Here, we analysed data from a published study with auditory cues used to reactivate visual object-location memories during slow-wave sleep. We characterized effects of Memory reactivation on brain network connectivity using graph-theory. We found that cue presentation during slow-wave sleep increased global network integration of occipital cortex, a visual region that was also active during retrieval of object locations. Although cueing did not have an overall beneficial effect on the retention of cued versus uncued associations, individual differences in overnight Memory Stabilization were related to enhanced network integration of occipital cortex. Furthermore, occipital cortex displayed enhanced connectivity with mnemonic regions, namely the hippocampus, parahippocampal gyrus, thalamus and medial prefrontal cortex during cue sound presentation. Together, these results suggest a neural mechanism where cue-induced replay during sleep increases integration of task-relevant perceptual regions with mnemonic regions. This cross-regional integration may be instrumental for the consolidation and long-term storage of enduring memories.
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Cued reactivation during slow-wave sleep induces connectivity changes related to Memory Stabilization.
2017Co-Authors: Ruud Berkers, Atsuko Takashima, Matthias Ekman, Eelco V. Van Dongen, Marcus Barth, Ken A. Paller, Guillén FernándezAbstract:Memory reprocessing following acquisition enhances Memory consolidation. Specifically, neural activity during encoding is thought to be replayed during subsequent slow-wave sleep (SWS). This natural tendency of Memory replay can be induced by external cueing, known as targeted Memory reactivation. Here, we analyzed data from a published study (van Dongen, Takashima, et al. 2012), where auditory cues reactivated learned visual object-location memories during SWS. Memory replay during sleep presumably involves a shift in connectivity across the brain. Therefore, we characterized the effects of Memory reactivation on brain network connectivity using graph-theory. We found that cue presentation during SWS introduced increased network integration of the occipital cortex, a visual region that was also active during the object retrieval task. Importantly, enhanced network integration of the occipital cortex showed a behavioural benefit and predicted overnight Memory Stabilization. Furthermore, occipital cortex displayed enhanced connectivity with mnemonic regions, namely the hippocampus, parahippocampal gyrus, thalamus and medial prefrontal cortex during cue versus control sound presentation. Finally, network integration of early occipital cortex during cueing in SWS was related to increased activation of the bilateral parahippocampal gyrus, a region involved in coding for spatial associative information, at the post-sleep test. Together, these results support a neural mechanism where cue-induced replay during sleep promotes Memory consolidation by increased integration of task-relevant perceptual regions with mnemonic regions.
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Memory Stabilization with targeted reactivation during human slow-wave sleep
Proceedings of the National Academy of Sciences, 2012Co-Authors: Eelco V. Van Dongen, Atsuko Takashima, Ken A. Paller, Markus Barth, Jascha Zapp, Lothar R. Schad, Guillén FernándezAbstract:It is believed that neural representations of recent experiences become reactivated during sleep, and that this process serves to stabilize associated memories in long-term Memory. Here, we initiated this reactivation process for specific memories during slow-wave sleep. Participants studied 50 object-location associations with object-related sounds presented concurrently. For half of the associations, the related sounds were re-presented during subsequent slow-wave sleep while participants underwent functional MRI. Compared with control sounds, related sounds were associated with increased activation of right parahippocampal cortex. Postsleep Memory accuracy was positively correlated with sound-related activation during sleep in various brain regions, including the thalamus, bilateral medial temporal lobe, and cerebellum. In addition, postsleep Memory accuracy was also positively correlated with pre- to postsleep changes in parahippocampal-medial prefrontal connectivity during retrieval of reactivated associations. Our results suggest that the brain is differentially activated by studied and unstudied sounds during deep sleep and that the thalamus and medial temporal lobe are involved in establishing the mnemonic consequences of externally triggered reactivation of associative memories.
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Visual areas become less engaged in associative recall following Memory Stabilization.
NeuroImage, 2008Co-Authors: Ingrid L.c. Nieuwenhuis, Atsuko Takashima, Robert Oostenveld, Guillén Fernández, Ole JensenAbstract:Numerous studies have focused on changes in the activity in the hippocampus and higher association areas with consolidation and Memory Stabilization. Even though perceptual areas are engaged in Memory recall, little is known about how Memory Stabilization is reflected in those areas. Using magnetoencephalography (MEG) we investigated changes in visual areas with Memory Stabilization. Subjects were trained on associating a face to one of eight locations. The first set of associations ('stabilized') was learned in three sessions distributed over a week. The second set ('labile') was learned in one session just prior to the MEG measurement. In the recall session only the face was presented and subjects had to indicate the correct location using a joystick. The MEG data revealed robust gamma activity during recall, which started in early visual cortex and propagated to higher visual and parietal brain areas. The occipital gamma power was higher for the labile than the stabilized condition (time=0.65-0.9 s). Also the event-related field strength was higher during recall of labile than stabilized associations (time=0.59-1.5 s). We propose that recall of the spatial associations prior to Memory Stabilization involves a top-down process relying on reconstructing learned representations in visual areas. This process is reflected in gamma band activity consistent with the notion that neuronal synchronization in the gamma band is required for visual representations. More direct synaptic connections are formed with Memory Stabilization, thus decreasing the dependence on visual areas.