The Role of Medial Temporal Lobe Regions in Incidental and Intentional Retrieval of Item and Relational Information in Aging

Relationships between age, fMRI correlates of familiarity and familiarity-based memory performance under single and dual task conditions

Using fMRI, we investigated the effects of age and divided attention on the neural correlates of familiarity and their relationship with memory performance. At study, word pairs were visually presented to young and older participants under the requirement to make a relational judgment on each pair. Participants were then scanned while undertaking an associative recognition test under single and dual (auditory tone detection) task conditions. The test items comprised studied, rearranged (words from different studied pairs) and new word pairs. fMRI familiarity effects were operationalized as greater activity elicited by studied pairs incorrectly identified as 'rearranged' than by correctly rejected new pairs. The reverse contrast was employed to identify 'novelty' effects. Behavioral familiarity estimates were equivalent across age groups and task conditions. Robust fMRI familiarity effects were identified in several regions, including medial and superior lateral parietal cortex, dorsal medial and left lateral prefrontal cortex, and bilateral caudate. fMRI novelty effects were identified in the anterior medial temporal lobe. Both familiarity and novelty effects were largely age-invariant and did not vary, or varied minimally, according to task condition. In addition, the familiarity effects correlated positively with a behavioral estimate of familiarity strength irrespective of age. These findings extend a previous report from our laboratory, and converge with prior behavioral reports, in demonstrating that the factors of age and divided attention have little impact on behavioral and neural estimates of familiarity.

Incidental temporal binding in rats: A novel behavioral task

We designed a behavioral task called One-Trial Trace Escape Reaction (OTTER), in which rats incidentally associate two temporally discontinuous stimuli: a neutral acoustic cue (CS) with an aversive stimulus (US) which occurs two seconds later (CS-2s-US sequence). Rats are first habituated to two similar environmental contexts (A and B), each consisting of an interconnected dark and light chamber. Next, rats experience the CS-2s-US sequence in the dark chamber of one of the contexts (either A or B); the US is terminated immediately after a rat escapes into the light chamber. The CS-2s-US sequence is presented only once to ensure the incidental acquisition of the association. The recall is tested 24 h later when rats are presented with only the CS in the alternate context (B or A), and their behavioral response is observed. Our results show that 59% of the rats responded to the CS by escaping to the light chamber, although they experienced only one CS-2s-US pairing. The OTTER task offers a flexible high throughput tool to study memory acquired incidentally after a single experience. Incidental one-trial acquisition of association between temporally discontinuous events may be one of the essential components of episodic memory formation.

Relationships between age, fMRI correlates of familiarity and familiarity-based memory performance under single and dual task conditions

Using fMRI, we investigated the effects of age and divided attention on the neural correlates of familiarity and their relationship with memory performance. At study, word pairs were visually presented to young and older participants under the requirement to make a relational judgment on each pair. Participants were then scanned while undertaking an associative recognition test under single and dual (auditory tone detection) task conditions. The test items comprised studied, rearranged (words from different studied pairs) and new word pairs. fMRI familiarity effects were operationalized as greater activity elicited by studied pairs incorrectly identified as 'rearranged' than by correctly rejected new pairs. The reverse contrast was employed to identify 'novelty' effects. Behavioral familiarity estimates were equivalent across age groups and task conditions. Robust fMRI familiarity effects were identified in several regions, including medial and superior lateral parietal cortex, dorsal medial and left lateral prefrontal cortex, and bilateral caudate. fMRI novelty effects were identified in the anterior medial temporal lobe. Both familiarity and novelty effects were age-invariant and did not vary according to task condition. In addition, the familiarity effects correlated positively with a behavioral estimate of familiarity strength irrespective of age. These findings extend a previous report from our laboratory, and converge with prior behavioral reports, in demonstrating that the factors of age and divided attention have minimal impact on behavioral and neural estimates of familiarity.

The QuadMax Task: Parametrically Manipulating Associative Memory Load across the Adult Lifespan

Adults of all ages are worse at recognizing pairs of items that were previously seen together relative to the individual items, and this paired-associative memory deficit is exacerbated in aging. Less is known about memory for higher associative loads, which place greater demands on binding processes that link items into a cohesive memory trace, among other processes (e.g., working memory, recollection). In this study, adults across the lifespan (n = 250, 18-78 years) completed a novel recognition task in which they studied word pairs, triplets, and quadruplets and were tested on their memory for repeated, recombined, and novel word sets. Associative memory deficits were seen in adults of all ages as fewer correct responses to repeated sets (hits), more incorrect responses to recombined sets (recombined false alarm, FA), and larger differences between these measures (associative memory) at higher set sizes. In addition, older adults had worse associative memory performance (higher recombined FA, lower associative memory) that increased at higher set sizes. These findings indicate that associative memory deficits increase with demands on binding or other processes at higher associative loads and with aging. They further demonstrate the feasibility of manipulating and assessing associative memory load using our novel QuadMax task.

Divided attention at retrieval does not influence neural correlates of recollection in young or older adults

Age-related decline in episodic memory has been partially attributed to older adults' reduced domain general processing resources. In the present study, we examined the effects of divided attention (DA) - a manipulation assumed to further deplete the already limited processing resources of older adults - on the neural correlates of recollection in young and older adults. Participants underwent fMRI scanning while they performed an associative recognition test in single and dual (tone detection) task conditions. Recollection effects were operationalized as greater BOLD activity elicited by test pairs correctly endorsed as 'intact' than pairs correctly or incorrectly endorsed as 'rearranged'. Detrimental effects of DA on associative recognition performance were identified in older but not young adults. The magnitudes of recollection effects did not differ between the single and dual (tone detection) tasks in either age group. Across the task conditions, age-invariant recollection effects were evident in most members of the core recollection network. However, while young adults demonstrated robust recollection effects in left angular gyrus, angular gyrus effects were undetectable in the older adults in either task condition. With the possible exception of this result, the findings suggest that DA did not influence processes supporting the retrieval and representation of associative information in either young or older adults, and converge with prior behavioral findings to suggest that episodic retrieval operations are little affected by DA.

The effects of age on neural correlates of recognition memory: An fMRI study

Studies examining the effects of age on the neural correlates of recognition memory have yielded mixed results. In the present study, we employed a modified remember-know paradigm to compare the fMRI correlates of recollection and familiarity in samples of healthy young and older adults. After studying a series of words, participants underwent fMRI scanning during a test phase in which they responded "remember" to a test word if any qualitative information could be recollected about the study event. When recollection failed, participants signaled how confident they were that the test item had been studied. Young and older adults demonstrated statistically equivalent estimates of recollection and familiarity strength, while recognition memory accuracy was significantly lower in the older adults. Robust, age-invariant fMRI effects were evident in two sets of a priori defined brain regions consistently reported in prior studies to be sensitive to recollection and familiarity respectively. In addition, the magnitudes of 'familiarity-attenuation effects' in perirhinal cortex demonstrated age-invariant correlations with estimates of familiarity strength and memory accuracy, replicating prior findings. Together, the present findings add to the evidence that the neural correlates of recognition memory are largely stable across much of the healthy human adult lifespan.

Cognitive function and cerebellar morphometric changes relate to abnormal intra-cerebellar and cerebro-cerebellum functional connectivity in old adults

INTRODUCTION

Numerous structural studies have already reported volumetric reduction in cerebellum with aging. However, there are still limited studies particularly focusing on analysis of the cerebellar resting state FC in old adults. Even so, the least related studies were unable to include some important cerebellar lobules due to limited cerebellum segmentation methods.

OBJECTIVE

The purpose of this study is to explore cognitive function in relation to cerebellar lobular morphometry and cortico-cerebellar connectivity changes in old adults' lifespan by incorporating previously undetected cerebellar lobules.

METHODS

This study includes a sample of 264 old adults subdivided into five cognitively normal age groups (G1 through G5). Cerebellum Segmentation (CERES) software was used to obtain morphometric measures and brain masks of all the 24 cerebellar lobules. We then defined individual lobules as seed regions and mapped the whole-brain to get functional connectivity maps. To analyze age group differences in cortico-cerebellar connectivity and cerebellar lobular volume, we used one way ANOVA and post hoc analysis was performed for multiple comparisons using Bonferroni method.

RESULTS

Our results report cerebellar lobular volumetric reduction, disrupted intra-cerebellar connectivity and significant differences in cortico-cerebellar resting state FC across age groups. In addition, our results show that disrupted FC between left Crus-II and right ACC relates to well emotion regulation and cognitive decline and is associated with poor performance on TMT-B and logical memory tests in older adults.

CONCLUSION

Overall, our findings confirm that as humans get older and older, the cerebellar lobular volumes as well as the cortico-cerebellar functional connectivity are affected and hence reduces cognition.

Recollection-related hippocampal fMRI effects predict longitudinal memory change in healthy older adults

Prior fMRI studies have reported relationships between memory-related activity in the hippocampus and in-scanner memory performance, but whether such activity is predictive of longitudinal memory change remains unclear. Here, we administered a neuropsychological test battery to a sample of cognitively healthy older adults on three occasions, the second and third sessions occurring one month and three years after the first session. Structural and functional MRI data were acquired between the first two sessions. The fMRI data were derived from an associative recognition procedure and allowed estimation of hippocampal effects associated with both successful associative encoding and successful associative recognition (recollection). Baseline memory performance and memory change were evaluated using memory component scores derived from a principal components analysis of the neuropsychological test scores. Across participants, right hippocampal encoding effects correlated significantly with baseline memory performance after controlling for chronological age. Additionally, both left and right hippocampal associative recognition effects correlated negatively with longitudinal memory decline after controlling for age, and the relationship with the left hippocampal effect remained after also controlling for left hippocampal volume. Thus, in cognitively healthy older adults, the magnitude of hippocampal recollection effects appears to be a robust predictor of future memory change.

Detection of Mild Cognitive Impairment Based on Virtual Reality: A Scoping Review

BACKGROUND

To delay the decline in cognition and reduce the incidence of dementia, the precise detection of Mild Cognitive Impairment (MCI) is necessary. The application of Virtual Reality (VR) technology in this detection can overcome the shortage of traditional paper-and-pencil tests.

OBJECTIVE

This review aimed to summarize the research progress of the detection of MCI using VR.

METHODS

Eight databases from their inception to November 19, 2019, were systematically searched for studies applying VR in the detection of MCI. A thematic analysis was conducted according to the specific detection purpose and the main corresponding cognitive domains assessed were summarized; characteristics of the VR applications were also summarized.

RESULTS

Twenty-eight studies were finally included. The detection purposes included discrimination between healthy controls and those with MCI, discrimination between aMCI subtypes, detection of MCI patients at risk of Alzheimer's Disease (AD), and discrimination between MCI and AD. VR tasks assessing spatial memory were applicable for all detection purposes, and the assessment of combinations of memory and executive function seemed more sensitive. Executive function and intentional episodic memory could be assessed to discriminate among healthy controls, individuals with MCI and those with AD. Incidental episodic memory was effective in detecting MCI with hippocampal atrophy. The most common characteristics of the VR applications were the use of semi-immersion, joysticks or gamepad interactions and simple, one-time behavioral assessments.

CONCLUSION

VR applications are promising in the detection of MCI, but further research is needed for clinical use.

Incidental Learning: A Systematic Review of Its Effect on Episodic Memory Performance in Older Age

Episodic memory is the capacity to encode, store, and retrieve information of specific past events. Several studies have shown that the decline in episodic memory accompanies aging, but most of these studies assessed memory performance through intentional learning. In this approach, the individuals deliberately acquire knowledge. Yet, another method to evaluate episodic memory performance-receiving less attention by the research community-is incidental learning. Here, participants do not explicitly intent to learn. Incidental learning becomes increasingly important over the lifespan, since people spend less time in institutions where intentional learning is required (e.g., school, university, or at work). Yet, we know little how incidental learning impacts episodic memory performance in advanced age. Likewise, the neural mechanisms underlying incidental learning in older age remain largely unknown. Thus, the immediate goal of this review was to summarize the existing literature on how incidental learning changes with age and how neural mechanisms map onto these age-related changes. We considered behavioral as well as neuroimaging studies using incidental learning paradigms (alone or in combination with intentional learning) to assess episodic memory performance in elderly adults. We conducted a systematic literature search on the Medline/PubMed, Cochrane, and OVID SP databases and searched the reference lists of articles. The search yielded 245 studies, of which 34 concerned incidental learning and episodic memory in older adults. In sum, these studies suggest that aging particularly affects episodic memory after incidental learning for cognitively demanding tasks. Monitoring deficits in older adults might account for these findings since cognitively demanding tasks need increased attentional resources. On a neuronal level, dysregulation of the default-mode-network mirrors monitoring deficits, with an attempt to compensate through increased frontal activity. Future (neuroimaging) studies should systematically evaluate retrieval tasks with diverging cognitive load and consider the influence of attention and executive functions in more detail.

A Roadmap for Understanding Memory: Decomposing Cognitive Processes into Operations and Representations

Thanks to patients Phineas Gage and Henry Molaison, we have long known that behavioral control depends on the frontal lobes, whereas declarative memory depends on the medial temporal lobes (MTL). For decades, cognitive functions-behavioral control, declarative memory-have served as labels for characterizing the division of labor in cortex. This approach has made enormous contributions to understanding how the brain enables the mind, providing a systems-level explanation of brain function that constrains lower-level investigations of neural mechanism. Today, the approach has evolved such that functional labels are often applied to brain networks rather than focal brain regions. Furthermore, the labels have diversified to include both broadly-defined cognitive functions (declarative memory, visual perception) and more circumscribed mental processes (recollection, familiarity, priming). We ask whether a process-a high-level mental phenomenon corresponding to an introspectively-identifiable cognitive event-is the most productive label for dissecting memory. For example, recollection conflates a neurocomputational operation (pattern completion-based retrieval) with a class of representational content (associative, high-dimensional memories). Because a full theory of memory must identify operations and representations separately, and specify how they interact, we argue that processes like recollection constitute inadequate labels for characterizing neural mechanisms. Instead, we advocate considering the component operations and representations of processes like recollection in isolation. For the organization of memory, the evidence suggests that pattern completion is recapitulated widely across the ventral visual stream and MTL, but the division of labor between sites within this pathway can be explained by representational content.

Cutting out the middleman: Separating attributional biases from memory deficits

Bastin and colleagues present an integrative model of how recollection- and familiarity-based memories are represented in the brain. While they emphasize the role of attribution mechanisms in shaping memory retrieval, prior work examining implicit memory suggests that memory deficits may be better understood by separating attributional biases from the underlying memory traces.

Development and Decline of the Hippocampal Long-Axis Specialization and Differentiation During Encoding and Retrieval of Episodic Memories

Change in hippocampal function is a major factor in life span development and decline of episodic memory. Evidence indicates a long-axis specialization where anterior hippocampus is more engaged during encoding than during retrieval, and posterior more engaged during retrieval than during encoding. We tested the life span trajectory of hippocampal long-axis episodic memory-related activity and functional connectivity (FC) in 496 participants (6.8–80.8 years) encoding and retrieving associative memories. We found evidence for a long-axis encoding–retrieval specialization that declined linearly during development and aging, eventually vanishing in the older adults. This was mainly driven by age effects on retrieval, which was associated with gradually lower activity from childhood to adulthood, followed by positive age relationships until 70 years. This pattern of age effects characterized task engagement regardless of memory success or failure. Especially for retrieval, children engaged posterior hippocampus more than anterior, while anterior was relatively more activated already in teenagers. Significant intrahippocampal connectivity was found during task, which declined with age. The results suggest that hippocampal long-axis differentiation and communication during episodic memory tasks develop rapidly during childhood, are different in older compared with younger adults, and that the age effects are related to task engagement, not the successful retrieval of episodic memories specifically.

How do memory systems detect and respond to novelty?

The efficiency of the memory system lies not only in its readiness to detect and retrieve old stimuli but also in its ability to detect and integrate novel information. In this review, we discuss recent evidence suggesting that the neural substrates sensitive to detecting familiarity and novelty are not entirely overlapping. Instead, these partially distinct familiarity and novelty signals are integrated to support recognition memory decisions. We propose here that the mediodorsal thalamus is critical for familiarity detection, and for combining novelty signals from the medial temporal lobe cortex with the relative familiarity outputs of computations performed in other cortical structures, especially the prefrontal cortex. Importantly, we argue that the anterior hippocampus has a prominent role in detecting novelty and in communicating this with midbrain and striatal structures. We argue that different types of novelty (absolute or contextual) engage different neurotransmitter systems that converge in the hippocampus. We suggest that contextual or unexpected novelty triggers dopaminergic hippocampal-midbrain coupling and noradrenergic-mediated pupil dilation. In contrast, absolute novelty triggers cholinergic-mediated hippocampal encoding accompanied by diminished pupil dilation. These two, distinct hippocampal encoding mechanisms both lead to later recollection but are sensitive to different types of novelty. We conclude that this neurotransmitter-mediated hippocampal encoding establishes the hippocampus in an encoding mode that briefly prevents the engagement of retrieval.

Knowledge supports memory retrieval through familiarity, not recollection

Semantic memory, or general knowledge of the world, guides learning and supports the formation and retrieval of new episodic memories. Behavioral evidence suggests that this knowledge effect is supported by recollection-a more controlled form of memory retrieval generally accompanied by contextual details-to a greater degree than familiarity-a more automatic form of memory retrieval generally absent of contextual details. In the current study, we used functional magnetic resonance imaging (fMRI) to investigate the role that regions associated with recollection and familiarity play in retrieving recent instances of known (e.g., The Summer Olympic Games are held four years apart) and unknown (e.g., A flaky deposit found in port bottles is beeswing) statements. Our results revealed a surprising pattern: Episodic retrieval of known statements recruited regions associated with familiarity, but not recollection. Instead, retrieval of unknown statements recruited regions associated with recollection. These data, in combination with quicker reaction times for the retrieval of known than unknown statements, suggest that known statements can be successfully retrieved on the basis of familiarity, whereas unknown statements were retrieved on the basis of recollection. Our results provide insight into how knowledge influences episodic retrieval and demonstrate the role of neuroimaging in providing insights into cognitive processes in the absence of explicit behavioral responses.

Independent contributions of fMRI familiarity and novelty effects to recognition memory and their stability across the adult lifespan

The impact of age on the neural correlates of familiarity-driven recognition memory has received relatively little attention. Here, the relationships between age, the neural correlates of familiarity, and memory performance were investigated using an associative recognition test in young, middle-aged and older participants. Test items comprised studied, rearranged (items studied on different trials) and new word pairs. fMRI 'familiarity effects' were operationalized as greater activity for studied test pairs incorrectly identified as 'rearranged' than for correctly rejected new pairs. The reverse contrast was employed to identify 'novelty' effects. Estimates of familiarity strength were slightly but significantly lower for the older relative to the younger group. With the exception of one region in dorsal medial prefrontal cortex, fMRI familiarity effects (which were identified in medial and lateral parietal cortex, dorsal medial and left lateral prefrontal cortex, and bilateral caudate among other regions) did not differ significantly with age. Age-invariant 'novelty effects' were identified in the anterior hippocampus and the perirhinal cortex. When entered into the same regression model, familiarity and novelty effects independently predicted familiarity strength across participants, suggesting that the two classes of memory effect reflect functionally distinct mnemonic processes. It is concluded that the neural correlates of familiarity-based memory judgments, and their relationship with familiarity strength, are largely stable across much of the healthy adult lifespan.

The neural correlates of recollection and retrieval monitoring: Relationships with age and recollection performance

The relationships between age, retrieval-related neural activity, and episodic memory performance were investigated in samples of young (18-29yrs), middle-aged (43-55yrs) and older (63-76yrs) healthy adults. Participants underwent fMRI scanning during an associative recognition test that followed a study task performed on visually presented word pairs. Test items comprised pairs of intact (studied pairs), rearranged (items studied on different trials) and new words. fMRI recollection effects were operationalized as greater activity for studied pairs correctly endorsed as intact than for pairs incorrectly endorsed as rearranged. The reverse contrast was employed to identify retrieval monitoring effects. Robust recollection effects were identified in the core recollection network, comprising the hippocampus, along with parahippocampal and posterior cingulate cortex, left angular gyrus and medial prefrontal cortex. Retrieval monitoring effects were identified in the anterior cingulate and right dorsolateral prefrontal cortex. Neither recollection effects within the core network, nor the monitoring effects differed significantly across the age groups after controlling for individual differences in associative recognition performance. Whole brain analyses did however identify three clusters outside of these regions where recollection effects were greater in the young than in the other age groups. Across-participant regression analyses indicated that the magnitude of hippocampal and medial prefrontal cortex recollection effects, and both of the prefrontal monitoring effects, correlated significantly with memory performance. None of these correlations were moderated by age. The findings suggest that the relationships between memory performance and functional activity in regions consistently implicated in successful recollection and retrieval monitoring are stable across much of the healthy adult lifespan.