Rapid memory reactivation revealed by oscillatory entrainment

Episodic memory refers to humans' unique ability to mentally reconstruct past events. Neurocomputational models predict that remembering entails the reinstatement of brain activity that was present when an event was initially experienced [1-5], a claim that has recently gained support from functional imaging work in humans [6-14]. The nature of this reactivation, however, is still unclear. Cognitive models claim that retrieval is set off by an early reactivation of stored memory representations ("ecphory") [15-17]. However, reinstatement as found in imaging studies might also reflect postretrieval processes that operate on the products of retrieval and are thus a consequence rather than a precondition of remembering. Here, we used frequency entrainment as a novel method of tagging memories in the human electroencephalogram (EEG). Participants studied words presented on flickering backgrounds, entraining a steady-state brain response at either 6 or 10?Hz. We found that these frequency signatures rapidly reemerged during a later memory test when participants successfully recognized?a word. An additional behavioral experiment suggested that this reactivation occurs in the absence of conscious memory for the frequencies entrained during study. The findings provide empirical evidence for the role of rapid, likely unconscious memory reactivation during retrieval.     

Neuronal signalling of fear memory

The learning and remembering of fearful events depends on the integrity of the amygdala, but how are fear memories represented in the activity of amygdala neurons? Here, we review recent electrophysiological studies indicating that neurons in the lateral amygdala encode aversive memories during the acquisition and extinction of Pavlovian fear conditioning. Studies that combine unit recording with brain lesions and pharmacological inactivation provide evidence that the lateral amygdala is a crucial locus of fear memory. Extinction of fear memory reduces associative plasticity in the lateral amygdala and involves the hippocampus and prefrontal cortex. Understanding the signalling of aversive memory by amygdala neurons opens new avenues for research into the neural systems that support fear behaviour.     

When Learning and Remembering Compete: A Functional MRI Study

Recent functional neuroimaging evidence suggests a bottleneck between learning new information and remembering old information. In two behavioral experiments and one functional MRI (fMRI) experiment, we tested the hypothesis that learning and remembering compete when both processes happen within a brief period of time. In the first behavioral experiment, participants intentionally remembered old words displayed in the foreground, while incidentally learning new scenes displayed in the background. In line with a memory competition, we found that remembering old information was associated with impaired learning of new information. We replicated this finding in a subsequent fMRI experiment, which showed that this behavioral effect was coupled with a suppression of learning-related activity in visual and medial temporal areas. Moreover, the fMRI experiment provided evidence that left mid-ventrolateral prefrontal cortex is involved in resolving the memory competition, possibly by facilitating rapid switching between learning and remembering. Critically, a follow-up behavioral experiment in which the background scenes were replaced with a visual target detection task provided indications that the competition between learning and remembering was not merely due to attention. This study not only provides novel insight into our capacity to learn and remember, but also clarifies the neural mechanisms underlying flexible behavior.     

Episodic memory and autonoetic consciousness: a first-person approach

Episodic memory is identified with autonoetic consciousness, which gives rise to remembering in the sense of self-recollection in the mental re-enactment of previous events at which one was present. Autonoetic consciousness is distinguished from noetic consciousness, which gives rise to awareness of the past that is limited to feelings of familiarity or knowing. Noetic consciousness is identified not with episodic but with semantic memory, which involves general knowledge. A recently developed approach to episodic memory makes use of 'first-person' reports of remembering and knowing. Studies using this approach have revealed many independent variables that selectively affect remembering and others that selectively affect knowing. These studies can also be interpreted in terms of distinctiveness and fluency of processing. Remembering and knowing do not correspond with degrees of confidence in memory. Nor does remembering always control the memory response. There is evidence that remembering is selectively impaired in various populations, including not only amnesic patients and older adults but also adults with Asperger's syndrome. This first-person approach to episodic memory represents one way in which that most elusive aspect of consciousness, its subjectivity, can be investigated scientifically. The two kinds of conscious experiences can be manipulated experimentally in ways that are systematic, replicable and intelligible theoretically.     

Motor cortex rules for learning and memory

Primary motor cortex has a complex, interconnected anatomical and functional architecture with dynamic properties. Recent evidence suggests that, concomitantly with regulating muscle activity and movements, the motor cortex makes key contributions to learning and remembering motor skills.     

The neurobiology of the human memory

Memory can be defined as the ability to acquire, process, store, and retrieve information. Memory is indispensable for learning, adaptation, and survival of every living organism. In humans, the remembering process has acquired great flexibility and complexity, reaching close links with other mental functions, such as thinking and emotions. Changes in synaptic connectivity and interactions among multiple neural networks provide the neurobiological substrates for memory encoding, retention, and consolidation. Memory may be categorized as short-term and long-term memory (according to the storage temporal duration), as implicit and explicit memory (with respect to the consciousness of remembering), as declarative (knowing that [fact]) and procedural (knowing how [skill]) memory, or as sensory (echoic, iconic and haptil), semantic, and episodic memory (according to the various remembering domains). Significant advances have been obtained in understanding memory neurobiology, but much remains to be learned in its cognitive, psychological, and phenomenological aspects.     

Does Time Really Slow Down during a Frightening Event?

Observers commonly report that time seems to have moved in slow motion during a life-threatening event. It is unknown whether this is a function of increased time resolution during the event, or instead an illusion of remembering an emotionally salient event. Using a hand-held device to measure speed of visual perception, participants experienced free fall for 31 m before landing safely in a net. We found no evidence of increased temporal resolution, in apparent conflict with the fact that participants retrospectively estimated their own fall to last 36% longer than others' falls. The duration dilation during a frightening event, and the lack of concomitant increase in temporal resolution, indicate that subjective time is not a single entity that speeds or slows, but instead is composed of separable subcomponents. Our findings suggest that time-slowing is a function of recollection, not perception: a richer encoding of memory may cause a salient event to appear, retrospectively, as though it lasted longer.     

Re-Imagining the Future: Repetition Decreases Hippocampal Involvement in Future Simulation

Imagining or simulating future events has been shown to activate the anterior right hippocampus (RHC) more than remembering past events does. One fundamental difference between simulation and memory is that imagining future scenarios requires a more extensive constructive process than remembering past experiences does. Indeed, studies in which this constructive element is reduced or eliminated by “pre-imagining” events in a prior session do not report differential RHC activity during simulation. In this fMRI study, we examined the effects of repeatedly simulating an event on neural activity. During scanning, participants imagined 60 future events; each event was simulated three times. Activation in the RHC showed a significant linear decrease across repetitions, as did other neural regions typically associated with simulation. Importantly, such decreases in activation could not be explained by non-specific linear time-dependent effects, with no reductions in activity evident for the control task across similar time intervals. Moreover, the anterior RHC exhibited significant functional connectivity with the whole-brain network during the first, but not second and third simulations of future events. There was also evidence of a linear increase in activity across repetitions in right ventral precuneus, right posterior cingulate and left anterior prefrontal cortex, which may reflect source recognition and retrieval of internally generated contextual details. Overall, our findings demonstrate that repeatedly imagining future events has a decremental effect on activation of the hippocampus and many other regions engaged by the initial construction of the simulation, possibly reflecting the decreasing novelty of simulations across repetitions, and therefore is an important consideration in the design of future studies examining simulation.     

Eye movements predict recollective experience

Previously encountered stimuli can bring to mind a vivid memory of the episodic context in which the stimulus was first experienced ("remembered" stimuli), or can simply seem familiar ("known" stimuli). Past studies suggest that more attentional resources are required to encode stimuli that are subsequently remembered than known. However, it is unclear if the attentional resources are distributed differently during encoding and recognition of remembered and known stimuli. Here, we record eye movements while participants encode photos, and later while indicating whether the photos are remembered, known or new. Eye fixations were more clustered during both encoding and recognition of remembered photos relative to known photos. Thus, recognition of photos that bring to mind a vivid memory for the episodic context in which they were experienced is associated with less distributed overt attention during encoding and recognition. The results suggest that remembering is related to encoding of a few distinct details of a photo rather than the photo as a whole. In turn, during recognition remembering may be trigged by enhanced memory for the salient details of the photos.     

Episodic memory and common sense: how far apart?

Research has revealed facts about human memory in general and episodic memory in particular that deviate from both common sense and previously accepted ideas. This paper discusses some of these deviations in light of the proceedings of The Royal Society's Discussion Meeting on episodic memory. Retrieval processes play a more critical role in memory than commonly assumed; people can remember events that never happened; and conscious thoughts about one's personal past can take two distinct forms-'autonoetic' remembering and 'noetic' knowing. The serial-dependent-independent (SPI) model of the relations among episodic, semantic and perceptual memory systems accounts for a number of puzzling phenomena, such as some amnesic patients' preserved recognition memory and their ability to learn new semantic facts, and holds that episodic remembering of perceptual information can occur only by virtue of its mediation through semantic memory. Although common sense endows many animals with the ability to remember their past experiences, as yet there is no evidence that humanlike episodic memory-defined in terms of subjective time, self, and autonoetic awareness-is present in any other species.     

La schizophrénie, pathologie de la conscience? Ou comment les bonnes idées peuvent renaître...

Episodic memory corresponds to a state of consciousness called “autonoetic” which is characterized by the fact the subject is able to consciously remember a past personal life event. The subject is able to recall his autobiographical life, personal and individual and to encompass consciously a future prefiguration by the means of the autonoetic consciousness. The unique and personal characteristics of our memories are linked to relations between conscious remembering and self consciousness. This link can explain that the same event being lived by different subjects can lead to different reported memories. Conscious remembering is a phenomenon that highly contributes to one’s own identity building. Subjective conscious remembering which accompanies the personal memory recuperation is impaired in schizophrenics. This subjective conscious remembering state impairment will provoke the loss or alteration of the capacity of past event revival. Conscious remembering is impaired whereas familiarity is preserved in schizophrenics. Conscious remembering deficit is both quantitative and qualitative: we can observe a fragmentation of the subjective experience, schizophrenics are not able to gather different parts of an event to build a unique representation. This conscious remembering deficit is secondary to an impairment of episodic memories construction. The Jean-Marie Danion’s model places the specific disease deficit at the top of the cognitive building, the consciousness level. This deficit would produce the cognitive dysfunctions shape observed in schizophrenia and would be at the origin of some of the symptoms of the disease.     

The Differential Outcomes Effect in Pigeons (Columba livia): Is It Truly Anticipatory?

We used delay-interval interference to investigate the nature of the differential outcomes effect (DOE) in pigeons. Birds were trained on a delayed matching-to-sample (DMS) task under either common outcome or differential outcome conditions, and then presented with visual interference during the delay period. Consistent with previous literature, the common outcomes birds were slower to learn the DMS task than the differential outcomes birds. The common outcome birds were also more impaired by the visual interference than the differential outcomes birds. Our findings are consistent with the view that the birds trained with common outcomes were likely remembering the sample stimulus during the delay period, and hence were disrupted by the visual interference, whereas the birds trained with differential outcomes were likely relying on the different emotional reactions elicited by the different outcomes to guide their choice behaviour, and hence were less affected by the visual interference. Our findings suggest that the DOE is not truly evidence of anticipatory mediation of short-term retention in pigeons, but rather emotionally driven decision making, which is not truly anticipatory in nature.     

Memory strategies of elderly: training efficacy

Does memory strategy training improve the quantity and quality of reported strategy use of normal older adults (N = 111, mean age 63 years, range 46-85 years) in daily life? Three strategy training conditions, remembering names (N = 26), intentions (N = 20) and verbal information (N = 20) and an educational training (N = 23) were compared to a test-retest control group (N = 22). Strategy use was assessed with a Strategy Frequency Questionnaire (investigating the reported frequency of strategy use on five scales: encoding, retrieval, general, external and no strategies) and a Memory Situations Questionnaire (investigating the preference of strategies in specific situations). Three months after training, the frequency of strategy use as assessed by the scale scores had not increased more in the strategy training conditions than in the control condition. No demographic or psychological characteristics were identified that could predict which individuals were most likely to change their strategy use. When strategies were analyzed separately, only after names training a specific effect was demonstrated, indicating that subjects more frequently used the strategy for remembering names (association) at follow-up. With regard to changes in the strategies used in specific situations, subjects in the names and intention training conditions reported an increase in the use of the trained strategies on names and prospective situations respectively. Moreover, there was some evidence of a generalization of training to strategies that were not directly dealt with during training. The control group showed that repeated practice with memory tests may result in changes in strategy use in specific situations, which are not always for the better, how-ever.     

Long-term memory retention in a wild fish species Labroides dimidiatus eleven months after an aversive event

Memory is essential to enhance future survival and reproduction as it helps in storing and retrieving useful information to solve particular environmental problems. However, we lack quantitative evidence on how far animals in the wild can maintain given information for extended periods without reinforcement. Here, we document correlative evidence of cleaner fish Labroides dimidiatus remembering being caught in a barrier net for up to 11 months. In 2015, about 60% of cleaners from one large isolated reef had been used for laboratory experiments and then returned to their site of capture. Eleven months later, 50% of cleaners at the same site showed an unusual hiding response to the placement of the barrier net, in contrast to three control sites where no cleaners had been caught during the last 2 years. The results suggest that a single highly aversive event (i.e., being caught in a barrier net) resulted in cleaners storing long-term crucial information that allowed them to avoid being caught again. Our results further our knowledge of fish cognitive capacities and long-term memory retention.     

The inheritance of neuropsychological dysfunction in twins discordant for schizophrenia

While genetic influences in schizophrenia are substantial, the disorder's molecular genetic basis remains elusive. Progress has been hindered by lack of means to detect nonpenetrant carriers of the predisposing genes and by uncertainties concerning the extent of locus heterogeneity. One approach to solving this complexity is to examine the inheritance of pathophysiological processes mediating between genotype and disease phenotype. Here we evaluate whether deficits in neurocognitive functioning covary with degree of genetic relationship with a proband in the unaffected MZ and DZ co-twins of patients with schizophrenia. Twin pairs discordant for schizophrenia were recruited from a total population cohort and were compared with a demographically balanced sample of control twin pairs, on a comprehensive neuropsychological test battery. The following four neuropsychological functions contributed uniquely to the discrimination of degree of genetic loading for schizophrenia and, when combined, were more highly correlated within MZ pairs than within DZ pairs, in both discordant and control twins: spatial working memory (i.e., remembering a sequence of spatial locations over a brief delay), divided attention (i.e., simultaneous performance of a counting and visual-search task), intrusions during recall of a word list (i.e., "remembering" nonlist items), and choice reaction time to visual targets. Together with evidence from human and animal studies of mediation of these functions by partially distinct brain systems, our findings suggest that there are multiple independently inherited dimensions of neural deficit in schizophrenia and encourage a search for genes contributing to quantitative variation in discrete aspects of disease liability. On tests of verbal and visual episodic memory, but not on the liability-related measures, patients were more impaired than their own MZ co-twins, suggesting a preferential impact of nongenetic influences on long-term memory systems.     

The mechanism of verbal memory and scenario of the development of speech V-rhythms

It was shown that the Feigenbaum scenario for the transition of bifurcation of period doubling to chaos, which explains the singularities of V-rhythm disorders in the neighborhood of the critical point, is a good model of the development of phonetics in children speech. It was also shown that the singularities of the dynamics of V-rhythms in the bifurcation lacuna in the zone of chaos intrinsic to the Pomeau-Manneville scenario for route of bifurcations of period 3 to chaos are capable, basically, to describe some features of both remembrance at the extraction from memory during speech and remembering in memory during perception of speech.     

Memory,consciousness and neuroimaging.

Neuroimaging techniques that allow the assessment of memory performance in healthy human volunteers while simultaneously obtaining measurements of brain activity in vivo may offer new information on the neural correlates of particular forms of memory retrieval and their association with consciousness and intention. We consider evidence from studies with positron emission tomography and functional magnetic resonance imaging indicating that priming, a form of implicit retrieval, is associated with decreased activity in various cortical regions. We also consider evidence concerning the question of whether two components of explicit retrieval--intentional or effortful search and successful conscious recollection--are preferentially associated with increased activity in prefrontal and medial temporal regions, respectively. Last, we consider recent efforts to probe the relation between the phenomenological character of remembering and neural activity. In this instance we broaden our scope to include studies employing event-related potentials and consider evidence concerning the neural correlates of qualitatively different forms of memory, including memory that is specifically associated with a sense of self, and the recollection of particular temporal or perceptual features that might contribute to a rich and vivid experience of the past.     

When encoding yields remembering: insights from event-related neuroimaging.

To understand human memory, it is important to determine why some experiences are remembered whereas others are forgotten. Until recently, insights into the neural bases of human memory encoding, the processes by which information is transformed into an enduring memory trace, have primarily been derived from neuropsychological studies of humans with select brain lesions. The advent of functional neuroimaging methods, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), has provided a new opportunity to gain additional understanding of how the brain supports memory formation. Importantly, the recent development of event-related fMRI methods now allows for examination of trial-by-trial differences in neural activity during encoding and of the consequences of these differences for later remembering. In this review, we consider the contributions of PET and fMRI studies to the understanding of memory encoding, placing a particular emphasis on recent event-related fMRI studies of the Dm effect: that is, differences in neural activity during encoding that are related to differences in subsequent memory. We then turn our attention to the rich literature on the Dm effect that has emerged from studies using event-related potentials (ERPs). It is hoped that the integration of findings from ERP studies, which offer higher temporal resolution, with those from event-related fMRI studies, which offer higher spatial resolution, will shed new light on when and why encoding yields subsequent remembering.     

Lasting Firsts

Changes taking place in the rural South create opportunities for remembering that encourage pride and power among the downtrodden and dispossessed. Comparing the cultural context of the murder of an African American schoolteacher in 1921 and the suffering that led to the murder of a Mayan farmworker in 1992, this essay explores the question of how celebrations and struggles of everyday existence fit within local histories inspired by martyrdom and death. The author argues that remembering is most effective when the form and content of memory join in the little that remains behind us.     

Maintained generalization of delay-specific remembering

According to the discrimination hypothesis (White, 2002), remembering is a delay-specific discrimination made at the time of retrieval. In the present experiment the delay-specific nature of the discrimination was made explicit by making correct choices in a delayed matching-to-sample task performed by pigeons conditional on whether the retention interval was short or long. Retention interval was varied over several durations in a maintained generalization test without reinforcement for correct matching responses. Opposing gradients demonstrated generalization of delay-specific remembering, consistent with the view that the temporal dimension of the retention interval can be treated in the same way as non-temporal dimensions of the sample stimulus.