Existing semantic knowledge provides a schematic scaffold for inference in early cognitive decline, but not in amnestic MCI

Age-Related differences in the relationship between sustained attention and associative memory and Memory-Guided inference

Episodic memory enables the encoding and retrieval of novel associations, as well as the bridging across learned associations to draw novel inferences. A fundamental goal of memory science is to understand the factors that give rise to individual and age-related differences in memory-dependent cognition. Variability in episodic memory could arise, in part, from both individual differences in sustained attention and diminished attention in aging. We first report that, relative to young adults (N = 23; M = 20.0 years), older adults (N = 26, M = 68.7 years) demonstrated lower associative memory and memory-guided associative inference performance and that this age-related reduction in associative inference occurs even when controlling for associative memory performance. Next, we confirm these age-related memory differences by using a high-powered, online replication study (young adults: N = 143, M = 26.2 years; older adults N = 133, M = 67.7 years), further demonstrating that age-related differences in memory do not reflect group differences in sustained attention (as assayed by the gradual-onset continuous performance task; gradCPT). Finally, we report that individual differences in sustained attention explain between-person variability in associative memory and inference performance in the present, online young adult sample, but not in the older adult sample. These findings extend understanding of the links between attention and memory in young adults, demonstrating that differences in sustained attention was related to differences in memory-guided inference. By contrast, our data suggest that the present age-related differences in memory-dependent behavior and the memory differences between older adults are due to attention-independent mechanisms.

Ask how they did it: untangling the relationships between task-specific strategy use, everyday strategy use, and associative memory

OBJECTIVE

Past research has shown that self-reported everyday strategy use and task-specific strategy use are related to associative memory performance in aging. Understudied is the relationship between these types of strategy use, whether they predict associative memory performance, and how this may differ across genders.

METHOD

A sample of older adults (N = 566, 53% female, ages 60-80) completed this online study. Study measures included 1. Multifactorial Memory Questionnaire (MMQ) Strategy Use subscale, a self-report measure of everyday strategy use, 2. Face-Name Task (FNT), a measure of associative memory, and 3. self-initiated number and types of strategies used on the FNT. Analyses examined the interrelationships among all study measures and their relative contributions to FNT performance while accounting for intraindividual factors.

RESULTS

Participants who reported using more strategies on the FNT performed better than those who used fewer or no strategies; those who reported using at least three strategies and relating FNT to past experience performed best. Women outperformed men on the FNT but did not differ in task-specific strategy use. Participants who reported using no strategies on the FNT had lower MMQ Strategy Use scores. A multiple regression analysis indicated that female gender and using at least two task strategies were significant predictors of greater FNT performance.

CONCLUSIONS

The results indicate that task-specific strategy use relates more to associative memory performance than to everyday strategy use, but neither accounts for the female advantage in FNT performance. Findings encourage querying task-specific strategy use to contextualize age-related associative memory decline.

The relationship between resting-state amplitude fluctuations and memory-related deactivations of the default mode network in young and older adults

The default mode network (DMN) typically exhibits deactivations during demanding tasks compared to periods of relative rest. In functional magnetic resonance imaging (fMRI) studies of episodic memory encoding, increased activity in DMN regions even predicts later forgetting in young healthy adults. This association is attenuated in older adults and, in some instances, increased DMN activity even predicts remembering rather than forgetting. It is yet unclear whether this phenomenon is due to a compensatory mechanism, such as self-referential or schema-dependent encoding, or whether it reflects overall reduced DMN activity modulation in older age. We approached this question by systematically comparing DMN activity during successful encoding and tonic, task-independent, DMN activity at rest in a sample of 106 young (18-35 years) and 111 older (60-80 years) healthy participants. Using voxel-wise multimodal analyses, we assessed the age-dependent relationship between DMN resting-state amplitude (mean percent amplitude of fluctuation, mPerAF) and DMN fMRI signals related to successful memory encoding, as well as their modulation by age-related hippocampal volume loss, while controlling for regional grey matter volume. Older adults showed lower resting-state DMN amplitudes and lower task-related deactivations. However, a negative relationship between resting-state mPerAF and subsequent memory effect within the precuneus was observed only in young, but not older adults. Hippocampal volumes showed no relationship with the DMN subsequent memory effect or mPerAF. Lastly, older adults with higher mPerAF in the DMN at rest tend to show higher memory performance, pointing towards the importance of a maintained ability to modulate DMN activity in old age.

Healthy Middle-Aged Adults Have Preserved Mnemonic Discrimination and Integration, While Showing No Detectable Memory Benefits

Declarative memory abilities change across adulthood. Semantic memory and autobiographic episodic knowledge can remain stable or even increase from mid- to late adulthood, while episodic memory abilities decline in later adulthood. Although it is well known that prior knowledge influences new learning, it is unclear whether the experiential growth of knowledge and memory traces across the lifespan may drive favorable adaptations in some basic memory processes. We hypothesized that an increased reliance on memory integration may be an adaptive mechanism to handle increased interference from accumulating memory traces and knowledge across adulthood. In turn, this may confer an improved ability for integration, observable in middle-age, before the onset of major aging-related declines. We further tested whether the hypothesized increase would be associated with previously observed reductions in memory discrimination performance in midlife. Data from a sample of healthy middle-aged (40-50 years, n = 40) and younger adults (20-28 years, n = 41) did not support the hypothesis of improved integration, as assessed by an associative inference paradigm. Instead, age-equivalent performance on both integration and discrimination measures were observed [Bayes factors (BFs)10 = 0.19-0.25], along with expected higher verbal knowledge and slower perceptual speed for middle-aged [(BFs)10 = 8.52-73.52]. The results contribute to an increased understanding of memory processing in midlife, an understudied portion of the lifespan, and suggest that two core episodic memory processes, integration and discrimination, can be maintained in healthy middle-aged adults.

The Role of the Ventromedial Prefrontal Cortex and Basal Forebrain in Relational Memory and Inference

The ventromedial prefrontal cortex (vmPFC) is involved in diverse cognitive operations, from inhibitory control to processing of semantic schemas. When accompanied by damage to the basal forebrain, vmPFC lesions can also impair relational memory, the ability to form and recall relations among items. Impairments in establishing direct relations among items (e.g., A is related to B, B is related to C) can also hinder the transitive processing of indirect relationships (e.g., inferring that A and C are related through direct relations that each contain B). Past work has found that transitive inference improves when the direct relations are organized within an existing knowledge structure, or schema. This type of semantic support is most effective for individuals whose relational memory deficits are mild (e.g., healthy age-related decline) rather than pronounced (e.g., hippocampal amnesia, amnestic mild cognitive impairment). Given that vmPFC damage can produce both relational memory and schema processing deficits, such damage may pose a particular challenge in establishing the type of relational structure required for transitive inference, even when supported by preexisting knowledge. To examine this idea, we tested individuals with lesions to the mPFC on multiple conditions that varied in pre-experimental semantic support and explored the extent to which they could identify both previously studied (direct) and novel transitive (indirect) relations. Most of the mPFC cases showed marked transitive inference deficits and even showed impaired knowledge of preexisting, direct, semantic relations, consistent with disruptions to schema-related processes. However, one case with more dorsal mPFC damage showed preserved ability to identify direct relations and make novel inferences, particularly when pre-experimental knowledge could be used to support performance. These results suggest that damage to the mPFC and basal forebrain can impede establishment of ad hoc relational schemas upon which transitive inference is based, but that appealing to prior knowledge may still be useful for those neurological cases that have some degree of preserved relational memory.

Learning by Insight-Like Sudden Comprehension as a Potential Strategy to Improve Memory Encoding in Older Adults

Several cognitive functions show a decline with advanced age, most prominently episodic memory. Problem-solving by insight represents a special associative form of problem-solving that has previously been shown to facilitate long-term memory formation. Recent neuroimaging evidence suggests that the encoding network involved in insight-based memory formation is largely hippocampus-independent. This may represent a potential advantage in older adults, as the hippocampus is one of the earliest brain structures to show age-related volume loss and functional impairment. Here, we investigated the potential beneficial effects of learning by insight in healthy older (60-79 years) compared to young adults (19-28 years). To this end, we compared later memory performance for verbal riddles encoded incidentally via induced insight-like sudden comprehension in both age groups. We employed a variant of the Compound Remote Associate Task (CRAT) for incidental encoding, during which participants were instructed to judge the solvability of items. In a 24-h delayed surprise memory test, participants attempted to solve previously encountered items and additionally performed a recognition memory test. During this test, older adults correctly solved an equal proportion of new CRA items compared to young adults and both age groups reported a similar frequency of Aha! experiences. While overall memory performance was better in young participants (higher proportion of correctly solved and correctly recognized old CRA items), older participants exhibited a stronger beneficial effect of insight-like sudden comprehension on later recognition memory for CRA items. Our results suggest that learning via insight might constitute a promising approach to improve memory function in old age.

Resting State BOLD Variability of the Posterior Medial Temporal Lobe Correlates with Cognitive Performance in Older Adults with and without Risk for Cognitive Decline

Local brain signal variability [SD of the BOLD signal (SDBOLD]] correlates with age and cognitive performance, and recently differentiated Alzheimer's disease (AD) patients from healthy controls. However, it is unknown whether changes to SDBOLD precede diagnosis of AD or mild cognitive impairment. We compared ostensibly healthy older adult humans who scored below the recommended threshold on the Montreal cognitive assessment (MoCA) and who showed reduced medial temporal lobe (MTL) volume in a previous study ("at-risk" group, n = 20), with healthy older adults who scored within the normal range on the MoCA ("control" group, n = 20). Using multivariate partial least-squares analysis we assessed the correlations between SDBOLD and age, MoCA score, global fractional anisotropy, global mean diffusivity, and four cognitive factors. Greater SDBOLD in the MTL and occipital cortex positively correlated with performance on cognitive control/speed tasks but negatively correlated with memory scores in the control group. These relations were weaker in the at-risk group. A post hoc analysis assessed associations between MTL volumes and SDBOLD in both groups. This revealed a negative correlation, most robust in the at-risk group, between MTL SDBOLD and MTL subregion volumetry, particularly the entorhinal and parahippocampal regions. Together, these results suggest that the association between SDBOLD and cognition differs between the at-risk and control groups, which may be because of lower MTL volumes in the at-risk group. Our data indicate relations between MTL SDBOLD and cognition may be helpful in understanding brain differences in individuals who may be at risk for further cognitive decline.

Gradual learning and inflexible strategy use in amnesia: Evidence from case H.C

The value of case studies in informing our understanding of dissociations and interactions in memory was recognized early on by Endel Tulving, whose comprehensive work with the amnesic case K.C. helped to confirm distinctions between episodic and semantic memory. Following in this tradition, we examined memory and the use of cognitive strategies in the developmental amnesic case H.C., a young woman with structural abnormalities in the extended hippocampal system (Rosenbaum et al., 2014). H.C. was tested on two tasks, transitivity and transverse patterning, that each required learning the relations among items, and for the former, also examined the ability to make inferences across sets of relations. H.C. was tested across multiple sessions and demonstrated two seemingly contradictory patterns of performance: evidence of gradual learning, yet an inability to flexibly switch to a cognitive strategy that may otherwise benefit performance. Specifically, on the transitivity task, H.C. showed gradual learning of novel relations that led to successful inferential performance. On transverse patterning, H.C. showed some gradual learning of the relations among the objects across sessions, and expressed knowledge that the task followed 'rock-paper-scissors' rules. However, H.C. did not benefit from a unitization strategy, which had shown previous success with other amnesic cases (D'Angelo et al., 2015; Ryan, Moses, Barense, & Rosenbaum, 2013). H.C.'s over-reliance on 'rock-paper-scissors' rules, even in the face of alternate strategies, is suggestive of an inability to enact cognitive flexibility. Poor performance thus may have resulted from interference from the experimentally presented strategy on her self-imposed strategy. The present findings echo work reported by Tulving in case K.C. (Tulving, Hayman, & Macdonald, 1991). Whereas neurologically intact individuals may rely on the functions of the hippocampal system to rapidly learn new information and resolve interference, some individuals with hippocampal amnesia may learn information gradually, but such learning is particularly prone to interference, resulting in an inability to flexibly adapt to changes in the learning conditions in order to optimize performance.