Formation Of New Episodic Memories Research Articles

The importance of conceptual knowledge when becoming familiar with faces during naturalistic viewing

Although the ability to recognise familiar faces is a critical part of everyday life, the process by which a face becomes familiar in the real world is not fully understood. Previous research has focussed on the importance of perceptual experience. However, in natural viewing, perceptual experience with faces is accompanied by increased knowledge about the person and the context in which they are encountered. Although conceptual information is known to be crucial for the formation of new episodic memories, it requires a period of consolidation. It is unclear, however, whether a similar process occurs when we learn new faces. Using a natural viewing paradigm, we investigated how the context in which events are presented influences our understanding of those events and whether, after a period of consolidation, this has a subsequent effect on face recognition. The context was manipulated by presenting events in 1) the original sequence, or 2) a scrambled sequence. Although this manipulation was predicted to have a significant effect on conceptual understanding of events, it had no effect on overall visual experience with the faces. Our prediction was that this contextual manipulation would affect face recognition after the information has been consolidated into memory. We found that understanding of the narrative was greater for participants who viewed the movie in the original sequence compared to those that viewed the movie in a scrambled order. To determine if the context in which the movie was viewed had an effect on face recognition, we compared recognition in the original and scrambled condition. We found an overall effect of conceptual knowledge on face recognition. That is, participants who viewed the original sequence had higher face recognition compared to participants who viewed the scrambled sequence. However, our planned comparisons did not reveal a greater effect of conceptual knowledge on face recognition after consolidation. In an exploratory analysis, we found that overlap in conceptual knowledge between participants was significantly correlated with the overlap in face recognition. We also found that this relationship was greater after a period of consolidation. Together, these findings provide new insights into the role of non-visual, conceptual knowledge for face recognition during natural viewing.

Preexperimental stimulus familiarity modulates the effects of item repetition on source memory.

Previous studies have reported contradictory findings regarding the effects of item repetition on the subsequent encoding of contextual details associated with items (i.e., source memory). Whereas some studies reported repetition-induced enhancement in source memory, other studies observed repetition-induced impairment. To resolve these conflicting results, we examined the modulatory role of preexperimental stimulus familiarity in the relationship between item repetition and new source memory formation by orthogonally manipulating preexperimental stimulus familiarity and intraexperimental item repetition. In a series of experiments consisting of three phases (item repetition, item-source association, and source memory test), we found that item repetition impaired source memory for preexperimentally familiar items (famous faces or words), whereas the same manipulation improved source memory for preexperimentally novel items (nonfamous faces or pseudowords). Crucially, item repetition impaired, rather than improved, source memory for preexperimentally novel items when these items had been preexposed to participants before the three-phase procedure. Collectively, these findings provide strong evidence that preexperimental stimulus familiarity determines the relative costs and benefits of intraexperimental item repetition on the encoding of new item-source associations. By demonstrating the interaction between different types of stimulus familiarity, the present findings advance our understanding of how prior experience affects the formation of new episodic memories. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Cell-Biological Requirements for the Generation of Dentate Gyrus Granule Neurons.

The dentate gyrus (DG) receives highly processed information from the associative cortices functionally integrated in the trisynaptic hippocampal circuit, which contributes to the formation of new episodic memories and the spontaneous exploration of novel environments. Remarkably, the DG is the only brain region currently known to have high rates of neurogenesis in adults (Andersen et al., 1966, 1971). The DG is involved in several neurodegenerative disorders, including clinical dementia, schizophrenia, depression, bipolar disorder and temporal lobe epilepsy. The principal neurons of the DG are the granule cells. DG granule cells generated in culture would be an ideal model to investigate their normal development and the causes of the pathologies in which they are involved and as well as possible therapies. Essential to establish such in vitro models is the precise definition of the most important cell-biological requirements for the differentiation of DG granule cells. This requires a deeper understanding of the precise molecular and functional attributes of the DG granule cells in vivo as well as the DG cells derived in vitro. In this review we outline the neuroanatomical, molecular and cell-biological components of the granule cell differentiation pathway, including some growth- and transcription factors essential for their development. We summarize the functional characteristics of DG granule neurons, including the electrophysiological features of immature and mature granule cells and the axonal pathfinding characteristics of DG neurons. Additionally, we discuss landmark studies on the generation of dorsal telencephalic precursors from pluripotent stem cells (PSCs) as well as DG neuron differentiation in culture. Finally, we provide an outlook and comment critical aspects.

The Role of Visual Association Cortex in Associative Memory Formation across Development.

Associative learning underlies the formation of new episodic memories. Associative memory improves across development, and this age-related improvement is supported by the development of the hippocampus and pFC. Recent work, however, additionally suggests a role for visual association cortex in the formation of associative memories. This study investigated the role of category-preferential visual processing regions in associative memory across development using a paired associate learning task in a sample of 56 youths (age 6-19 years). Participants were asked to bind an emotional face with an object while undergoing fMRI scanning. Outside the scanner, participants completed a memory test. We first investigated age-related changes in neural recruitment and found linear age-related increases in activation in lateral occipital cortex and fusiform gyrus, which are involved in visual processing of objects and faces, respectively. Furthermore, greater activation in these visual processing regions was associated with better subsequent memory for pairs over and above the effect of age and of hippocampal and pFC activation on performance. Recruitment of these visual processing regions mediated the association between age and memory performance, over and above the effects of hippocampal activation. Taken together, these findings extend the existing literature to suggest that greater recruitment of category-preferential visual processing regions during encoding of associative memories is a neural mechanism explaining improved memory across development.

Accessing Real-Life Episodic Information from Minutes versus Hours Earlier Modulates Hippocampal and High-Order Cortical Dynamics.

It is well known that formation of new episodic memories depends on hippocampus, but in real-life settings (e.g., conversation), hippocampal amnesics can utilize information from several minutes earlier. What neural systems outside hippocampus might support this minutes-long retention? In this study, subjects viewed an audiovisual movie continuously for 25 min; another group viewed the movie in 2 parts separated by a 1-day delay. Understanding Part 2 depended on retrieving information from Part 1, and thus hippocampus was required in the day-delay condition. But is hippocampus equally recruited to access the same information from minutes earlier? We show that accessing memories from a few minutes prior elicited less interaction between hippocampus and default mode network (DMN) cortical regions than accessing day-old memories of identical events, suggesting that recent information was available with less reliance on hippocampal retrieval. Moreover, the 2 groups evinced reliable but distinct DMN activity timecourses, reflecting differences in information carried in these regions when Part 1 was recent versus distant. The timecourses converged after 4 min, suggesting a time frame over which the continuous-viewing group may have relied less on hippocampal retrieval. We propose that cortical default mode regions can intrinsically retain real-life episodic information for several minutes.

Slow-Theta-to-Gamma Phase-Amplitude Coupling in Human Hippocampus Supports the Formation of New Episodic Memories.

Phase-amplitude coupling (PAC) has been proposed as a neural mechanism for coordinating information processing across brain regions. Here we sought to characterize PAC in the human hippocampus, and in temporal and frontal cortices, during the formation of new episodic memories. Intracranial recordings taken as 56 neurosurgical patients studied and recalled lists of words revealed significant hippocampal PAC, with slow-theta activity (2.5-5 Hz) modulating gamma band activity (34-130 Hz). Furthermore, a significant number of hippocampal electrodes exhibited greater PAC during successful than unsuccessful encoding, with the gamma activity at these sites coupled to the trough of the slow-theta oscillation. These same conditions facilitate LTP in animal models, providing a possible mechanism of action for this effect in human memory. Uniquely in the hippocampus, phase preference during item encoding exhibited a biphasic pattern. Overall, our findings help translate between the patterns identified during basic memory tasks in animals and those present during complex human memory encoding. We discuss the unique properties of human hippocampal PAC and how our findings relate to influential theories of information processing based on theta-gamma interactions.

Dissociable Neural Mechanisms for Encoding Predictable and Unpredictable Events

Attention is a necessary condition for the formation of new episodic memories, yet little is known about how dissociable attentional mechanisms for "top-down" and "bottom-up" orienting contribute to encoding. Here, subjects performed an intentional encoding task in which to-be-learned items were interspersed with irrelevant stimuli such that subjects could anticipate the appearance of some study items but not others. Subjects were more likely to later remember stimuli whose appearance was predictable at encoding. Electroencephalographic data were acquired during the study phase of the experiment to assess how synchronous neural activity related to later memory for predictable stimuli (to which attention could be oriented in a top-down fashion) and unpredictable stimuli (which rely to a greater extent on bottom-up attentional orienting). Over left frontal regions, gamma-band activity (25-55 Hz) early (approximately 150 msec) in the epoch was a robust predictor of later memory for predictable items, consistent with an emerging view that links high-frequency neural synchrony to top-down attention. By contrast, later (approximately 400 msec) theta-band activity (4-8 Hz) over the left and midline frontal cortex predicted subsequent memory for unpredictable items, suggesting a role in bottom-up attentional orienting. These results reveal for the first time the contribution of dissociable attentional mechanisms to successful encoding and contribute to a growing literature dedicated to understanding the role of neural synchrony in cognition.

Neocortical Connectivity during Episodic Memory Formation

During the formation of new episodic memories, a rich array of perceptual information is bound together for long-term storage. However, the brain mechanisms by which sensory representations (such as colors, objects, or individuals) are selected for episodic encoding are currently unknown. We describe a functional magnetic resonance imaging experiment in which participants encoded the association between two classes of visual stimuli that elicit selective responses in the extrastriate visual cortex (faces and houses). Using connectivity analyses, we show that correlation in the hemodynamic signal between face- and place-sensitive voxels and the left dorsolateral prefrontal cortex is a reliable predictor of successful face–house binding. These data support the view that during episodic encoding, “top-down” control signals originating in the prefrontal cortex help determine which perceptual information is fated to be bound into the new episodic memory trace.

Theta and Gamma Oscillations during Encoding Predict Subsequent Recall

Electrophysiological and hemodynamic measures of human brain activity have been shown to distinguish between episodes of encoding items that are later recalled versus those that are not recalled (Paller and Wagner, 2002). Using intracranial recordings from 793 widespread cortical and subcortical sites in 10 epileptic patients undergoing invasive monitoring, we compared oscillatory power at frequencies ranging from 2 to 64 Hz as participants studied lists of common nouns. Significant increases in oscillatory power during encoding predicted subsequent recall, with this effect predominantly in the 4-8 Hz (theta) and 28-64 Hz (gamma) frequency bands. Sites exhibiting increased theta activity during successful encoding were clustered in right temporal and frontal cortex, whereas those exhibiting increased gamma activity appeared bilaterally at widespread cortical locations. These findings implicate theta and gamma oscillatory activity, across a widespread network of cortical regions, in the formation of new episodic memories.

Encoding and the Frontal Lobes: A Dissociation Between Retrograde and Anterograde Memories

Recent functional neuroimaging studies have suggested that different neural substrates within the frontal lobes are associated with memory encoding, retrieval and monitoring. If this is the case, then it should be possible to find frontal patients with selective deficits to these processes. However, most laboratory based memory tests (e.g. Wechsler Memory Scale) require a combination of all these processes making it hard to find clear dissociations between patients. Using tests of everyday memory, this study documents a clear dissociation between a frontal patient's (JB) impaired ability to retrieve events from the anterograde period relative to spared ability to retrieve events from the retrograde period. This is consistent with specific disruption to frontal mechanisms associated with encoding which disrupts the formation of new episodic memories. The defective mechanism may be related to more general aspects of cognitive processing (e.g. selection demands), but it is unlikely to reflect damage to working memory (as assessed by the n-back task) as there is a clear dissociation between spared performance on this task and impaired performance on a comparable episodic recognition memory task.