Hippocampal ripples and memory consolidation

Girardeau, Gabrielle; Zugaro, Michaël

doi:10.1016/j.conb.2011.02.005

Cited by 277 publications

(235 citation statements)

References 89 publications

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“…Also, in human intracranial recordings, ripple events (which have been intimately linked to replay) (see ref. 27 for review) have been observed both in HIPP as well as in ErC (28), but interestingly the number of ripple events during a postlearning nap correlated with later memory performance only for ErC ripples and not for HIPP ripples (29). It thus remains an open question whether we did not observe HIPP reactivation effects because the spatiotemporal resolution of the conventional fMRI used here is too low to detect such events in HIPP, or because memory-related offline reactivation is more robustly manifest in ErC in humans.…”

Section: Discussionmentioning

confidence: 99%

Awake reactivation predicts memory in humans

Staresina

Alink

Kriegeskorte

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

212

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How are new experiences transformed into memories? Recent findings have shown that activation in brain regions involved in the initial task performance reemerges during postlearning rest, suggesting that "offline activity" might be important for this transformation. It is unclear, however, whether such offline activity indeed reflects reactivation of individual learning experiences, whether the amount of event-specific reactivation is directly related to later memory performance, and what brain regions support such event-specific reactivation. Here, we used functional magnetic resonance imaging to assess whether event-specific reactivation occurs spontaneously during an active, postlearning delay period in the human brain. Applying representational similarity analysis, we found that successful recall of individual study events was predicted by the degree of their endogenous reactivation during the delay period. Within the medial temporal lobe, this reactivation was observed in the entorhinal cortex. Beyond the medial temporal lobe, event-specific reactivation was found in the retrosplenial cortex. Controlling for the levels of blood oxygen level-dependent activation and the serial position during encoding, the data suggest that offline reactivation might be a key mechanism for bolstering episodic memory beyond initial study processes. These results open a unique avenue for the systematic investigation of reactivation and consolidation of episodic memories in humans. E pisodic memory, our ability to mentally relive past events and experiences, is a fundamental property of the human mind. Although memory research in humans has largely focused on the study (encoding) and test (retrieval) components of memory paradigms, comparatively little is known about the processes occurring between those stages. Experiments recording brain activity during postlearning sleep found that the activity in regions engaged during awake task performance reemerges during sleep (1, 2). Moreover, externally reinstating a study context during sleep (presenting an olfactory stimulus that was present during encoding) has been found to bolster postsleep memory performance (3). However, whereas the beneficial role of sleep for memory is undisputed (for recent reviews, see refs. 4 and 5), it is unlikely that sleep is the sole state in which memory solidification occurs. Indeed, recent functional magnetic resonance imaging (fMRI) studies in humans showed that activation in task-specific regions can also be observed during offline wake periods and that the amount of postlearning activation in these task-specific regions correlates with later behavioral performance (6, 7).Although these data show that activation in task-specific regions during rest periods is related to later memory performance, direct evidence for the notion that individual experiences are reactivated during these offline periods is lacking. That is, although it has been shown that experimental reactivation of individual events (by presenting sounds associated to unique study mat...

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Section: Discussionmentioning

confidence: 99%

Awake reactivation predicts memory in humans

Staresina

Alink

Kriegeskorte

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

212

213

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“…These findings lead us to propose that the endocannabinoid-mediated decrease in noradrenaline release at hippocampal noradrenergic terminals is a key step in modulating nonemotional memory consolidation studied in the object-recognition task. In this regard, it has been shown that noradrenaline is able to modulate synchronized hippocampal activity that can interfere with nonemotional memory consolidation (49,50).…”

Section: Discussionmentioning

confidence: 99%

Peripheral and central CB1 cannabinoid receptors control stress-induced impairment of memory consolidation

Busquets-García

Gomis-González

Srivastava

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Stressful events can generate emotional memories linked to the traumatic incident, but they also can impair the formation of nonemotional memories. Although the impact of stress on emotional memories is well studied, much less is known about the influence of the emotional state on the formation of nonemotional memories. We used the novel object-recognition task as a model of nonemotional memory in mice to investigate the underlying mechanism of the deleterious effect of stress on memory consolidation. Systemic, hippocampal, and peripheral blockade of cannabinoid type-1 (CB1) receptors abolished the stress-induced memory impairment. Genetic deletion and rescue of CB1 receptors in specific cell types revealed that the CB1 receptor population specifically in dopamine β-hydroxylase (DBH)-expressing cells is both necessary and sufficient for stressinduced impairment of memory consolidation, but CB1 receptors present in other neuronal populations are not involved. Strikingly, pharmacological manipulations in mice expressing CB1 receptors exclusively in DBH + cells revealed that both hippocampal and peripheral receptors mediate the impact of stress on memory consolidation. Thus, CB1 receptors on adrenergic and noradrenergic cells provide previously unrecognized cross-talk between central and peripheral mechanisms in the stress-dependent regulation of nonemotional memory consolidation, suggesting new potential avenues for the treatment of cognitive aspects on stress-related disorders. memory consolidation | stress response | cannabinoid receptor | endocannabinoid system | noradrenergic signaling M emory consolidation is sensitive to emotion-related manipulations after acquisition (1). However, the underlying neurobiological mechanisms are only partly understood. Emotions can contribute to memorizing important life events (1, 2); they can also impair memory consolidation (2). Specifically, emotional arousal caused by stress has been studied extensively in animal models and in humans, and it has been reported to produce both facilitation and impairment of memory (3-5). Most studies that investigated the neural mechanisms mediating the effects of stress have focused on emotional memories; the mechanisms underlying the effects of acute stress on nonemotional memories are less understood.Acute stressful stimuli activate the sympathetic-adrenal system and the hypothalamic-pituitary-adrenal (HPA) axis (6, 7). Increased activity in the sympathetic-adrenal system involves a rapid release of adrenaline and noradrenaline from adrenal chromaffin cells and sympathetic nerve terminals, respectively (7). Moreover, stress-induced activation of the HPA axis involves the synthesis and secretion of glucocorticoids (cortisol in humans and corticosterone in most rodents) from the adrenal cortex (8). Both animal and human studies have shown that these stress hormones have profound effects on cognition by acting on specific brain regions involved in the processing of emotional stimuli (1, 9-12).The endocannabinoid system is an endogenous neur...

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“…Physiological ripples can be recorded in the non-epileptic hippocampus and parahippocampal structures in normal rats [42,43] and may reflect IPSPs generated by subsets of interneurons that regulate the discharges of principal cells [41]. The function of these physiological ripples is to consolidate synaptic plasticity and they are important for episodic memory [44] and memory consolidation [45]. In the neocortex, fast oscillations are induced in specific areas by sensory stimulation or during language and motor tasks in humans.…”

Section: High-frequency Oscillationsmentioning

confidence: 99%

Advances of Intracranial Electroencephalography in Localizing the Epileptogenic Zone

Jin

Wang

2016

Neurosci. Bull.

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Intracranial electroencephalography (iEEG) provides the best precision in estimating the location and boundary of an epileptogenic zone. Analysis of iEEG in the routine EEG frequency range (0.5-70 Hz) remains the basis in clinical practice. Low-voltage fast activity is the most commonly reported ictal onset pattern in neocortical epilepsy, and low-frequency high-amplitude repetitive spiking is the most commonly reported ictal onset pattern in mesial temporal lobe epilepsy. Recent studies using wideband EEG recording have demonstrated that examining higher (80-1000 Hz) and lower (0.016-0.5 Hz) EEG frequencies can provide additional diagnostic information and help to improve the surgical outcome. In addition, novel computational techniques of iEEG signal analysis have provided new insights into the epileptic network. Here, we review some of these recent advances. Although these sophisticated and advanced techniques of iEEG analysis show promise in localizing the epileptogenic zone, their utility needs to be further validated in larger studies.

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Hippocampal ripples and memory consolidation

Cited by 277 publications

References 89 publications

Awake reactivation predicts memory in humans

Awake reactivation predicts memory in humans

Peripheral and central CB1 cannabinoid receptors control stress-induced impairment of memory consolidation

Advances of Intracranial Electroencephalography in Localizing the Epileptogenic Zone

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