Increasing access to media in the 21st century has led to a rapid rise in the prevalence of media multitasking (simultaneous use of multiple media streams). Such behavior is associated with various cognitive differences, such as difficulty filtering distracting information and increased trait impulsivity. Given the rise in media multitasking by children, adolescents, and adults, a full understanding of the cognitive profile of media multitaskers is imperative. Here we investigated the relationship between chronic media multitasking and working memory (WM) and long-term memory (LTM) performance. Four key findings are reported (1) heavy media multitaskers (HMMs) exhibited lower WM performance, regardless of whether external distraction was present or absent; (2) lower performance on multiple WM tasks predicted lower LTM performance; (3) media multitasking-related differences in memory reflected differences in discriminability rather than decision bias; and (4) attentional impulsivity correlated with media multitasking behavior and reduced WM performance. These findings suggest that chronic media multitasking is associated with a wider attentional scope/higher attentional impulsivity, which may allow goal-irrelevant information to compete with goal-relevant information. As a consequence, heavy media multitaskers are able to hold fewer or less precise goal-relevant representations in WM. HMMs’ wider attentional scope, combined with their diminished WM performance, propagates forward to yield lower LTM performance. As such, chronic media multitasking is associated with a reduced ability to draw on the past—be it very recent or more remote—to inform present behavior.

Age-related episodic memory decline is characterized by striking heterogeneity across individuals. Hippocampal pattern completion is a fundamental process supporting episodic memory. Yet, the degree to which this mechanism is impaired with age, and contributes to variability in episodic memory, remains unclear. We combine univariate and multivariate analyses of fMRI data from a large cohort of cognitively normal older adults (N=100) to measure hippocampal activity and cortical reinstatement during retrieval of trial-unique associations. Trial-wise analyses revealed that (a) hippocampal activity scaled with reinstatement strength, (b) cortical reinstatement partially mediated the relationship between hippocampal activity and associative retrieval, (c) older age weakened cortical reinstatement and its relationship to memory behaviour. Moreover, individual differences in the strength of hippocampal activity and cortical reinstatement explained unique variance in performance across multiple assays of episodic memory. These results indicate that fMRI indices of hippocampal pattern completion explain within- and across-individual memory variability in older adults.

Objective:To determine if memory tasks with demonstrated sensitivity to hippocampal function can detect variance related to preclinical Alzheimer’s disease (AD) biomarkers, we examined associations between performance in three memory tasks and CSF Aβ42/Aβ40 and p-tau181 in cognitively unimpaired older adults (CU).Methods:CU enrolled in the Stanford Aging and Memory Study (N=153; age 68.78 ± 5.81 yrs; 94 female) completed a lumbar puncture and memory assessments. CSF Aβ42, Aβ40, and phosopho-tau181 (p-tau181) were measured with the automated Lumipulse G system in a single-batch analysis. Episodic memory was assayed using a standardized delayed recall composite, paired associate (word-picture) cued recall, and a mnemonic discrimination task that involves discrimination between studied ‘target’ objects, novel ‘foil’ objects, and perceptually similar ‘lure’ objects. Analyses examined cross-sectional relationships between memory performance, age, and CSF measures, controlling for sex and education.Results:Age and lower Aβ42/Aβ40 were independently associated with elevated p-tau181. Age, Aβ42/Aβ40, and p-tau181 were each associated with a) poorer associative memory and b) diminished improvement in mnemonic discrimination performance across levels of decreased task difficulty (i.e., target-lure similarity). P-tau mediated the effect of Aβ42/Aβ40 on memory. Relationships between CSF proteins and delayed recall were similar but non-significant. CSF Aβ42 was not significantly associated with p-tau181 or memory.Conclusions:Tests designed to tax hippocampal function are sensitive to subtle individual differences in memory among CU, and correlate with early AD-associated biomarker changes in CSF. These tests may offer utility for identifying cognitively unimpaired older adults with preclinical AD pathology.

2Age-related episodic memory decline is characterized by striking heterogeneity across 36 individuals. Hippocampal pattern completion is a fundamental process supporting episodic 37 memory. Yet, the degree to which this mechanism is impaired with age, and contributes to 38 variability in episodic memory, remains unclear. We combine univariate and multivariate 39 analyses of fMRI data from a large cohort of cognitively normal older adults (N=100; 60-82 40 yrs) to measure hippocampal activity and cortical reinstatement during retrieval of trial-41 unique associations. Trial-wise analyses revealed that hippocampal activity predicted 42 cortical reinstatement strength, and these two metrics of pattern completion independently 43 predicted retrieval success. However, increased age weakened cortical reinstatement and 44 its relationship to memory behaviour. Critically, individual differences in the strength of 45 hippocampal activity and cortical reinstatement explained unique variance in performance 46 across multiple assays of episodic memory. These results indicate that fMRI indices of 47 hippocampal pattern completion explain within-and across-individual memory variability in 48 older adults. 49 50 51 52 53 54 55 56 57 3 Episodic memory -in particular the ability to form and retrieve associations between multiple 58 event elements that comprise past experiences -declines with age (1-3). Retrieval of an 59 episodic memory relies critically on hippocampal-dependent pattern completion, which 60 entails reactivation of a stored memory trace by the hippocampus in response to a partial 61 cue, leading to replay of cortical activity patterns that were present at the time of memory 62 encoding (4-7). Given observed links between in vivo measures of pattern completion and 63 episodic remembering (8-10), and evidence of altered hippocampal function with age (11-64 12), changes in hippocampal pattern completion may play an important role in explaining 65 age-related impairments in episodic memory. While a leading hypothesis, the degree to 66 which the integrity of pattern completion can explain (a) trial-to-trial differences in episodic 67 remembering within older adults and (b) differences in memory performance between older 68 individuals remain underspecified. 69Functional MRI (fMRI) studies in younger adults suggest that hippocampal pattern 70 completion is associated with at least two key neural markers: (a) an increase in 71 hippocampal univariate activity (13-15) and (b) cortical reinstatement of content-specific 72 activity patterns present during encoding (16-18). Multivariate pattern analyses --machine 73 learning classification (19) and pattern similarity (20) --reveal evidence for cortical 74 reinstatement of categorical event features (10, 21-22) and event-specific details (23-25) 75 during successful recollection. Moreover, hippocampal and cortical metrics of pattern 76 completion covary, such that trial-wise fluctuations in hippocampal univariate retrieval 77 activity predict the strength of cortical r...

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