Markus Werkle-Bergner

Episodic memory across the lifespan: The contributions of associative and strategic components

The structural and functional brain circuitries supporting episodic memory undergo profound reorganization in childhood and old age. We propose a two-component framework that combines and integrates evidence from child development and aging. It posits that episodic memory builds on two interacting components: (a) the strategic component, which refers to memory control operations, and (b) the associative component, which refers to mechanisms that bind different features of a memory episode into a compound representation. We hypothesize that: (a) childrens difficulties in episodic memory primarily originate from low levels of strategic operations, and reflect the protracted development of the prefrontal cortex (PFC); (b) deficits in episodic memory performance among older adults originate from impairments in both strategic and associative components, reflecting senescent changes in the PFC and the medio-temporal lobes (MTL). Initial behavioral and neural evidence is consistent with both hypotheses. The two-component framework highlights the specificities of episodic memory in different age periods, helps to identify and dissociate its components, and contributes to understanding the interplay among maturation, learning, and senescence.

Hippocampal Subfield Volumes: Age, Vascular Risk, and Correlation with Associative Memory

Aging and age-related diseases have negative impact on the hippocampus (HC), which is crucial for such age-sensitive functions as memory formation, maintenance, and retrieval. We examined age differences in hippocampal subfield volumes in 10 younger and 19 older adults, and association of those volumes with memory performance in the older participants. We manually measured volumes of HC regions CA1 and CA2 (CA1–2), sectors CA3 and CA4 plus dentate gyrus (CA3–4/DG), subiculum, and the entorhinal cortex using a contrast-optimized high-resolution PD-weighted MRI sequence. Although, as in previous reports, the volume of one region (CA1–2) was larger in the young, the difference was due to the presence of hypertensive subjects among the older adults. Among older participants, increased false alarm rate in an associative recognition memory task was linked to reduced CA3–4/DG volume. We discuss the role of the DG in pattern separation and the formation of discrete memory representations.

Cortical EEG correlates of successful memory encoding : Implications for lifespan comparisons

In the course of their lives, individuals experience a myriad of events. Some of them leave stable traces, and others fade away quickly. Recent advances in functional imaging methods allow researchers to contrast neuronal patterns of remembered against not remembered events at initial encoding. Research on young adults using functional magnetic resonance imaging (fMRI), intracranial, and standard electroencephalographic (EEG) recordings has identified differences between remembered and not remembered items in patterns of medio-temporal and prefrontal brain activity. However, little is known about the ways in which such neuronal patterns of successful encoding evolve across the lifespan as a function of maturation, senescence, and the accumulation of experience. Here, we first review empirical evidence on neuronal correlates of successful memory from middle childhood to old age. Based on the observation that associative and strategic components of episodic memory seem to follow different age gradients, we propose a conceptual framework for predicting age changes in neuronal patterns of successful encoding.

Neuromodulation of associative and organizational plasticity across the life span: Empirical evidence and neurocomputational modeling

Developmental plasticity is the key mechanism that allows humans and other organisms to modify and adapt to contextual and experiential influences. Thus, reciprocal co-constructive interactions between behavioral and neuronal plasticity play important roles in regulating neurobehavioral development across the life span. This review focuses on behavioral and neuronal evidence of lifespan differences in associative memory plasticity and plasticity of the functional organization of cognitive and cortical processes, as well as the role of the dopaminergic system in modulating such plasticity. Special attention is given to neurocomputational models that help exploring lifespan differences in neuromodulation of neuronal and behavioral plasticity. Simulation results from these models suggest that lifespan changes in the efficacy of neuromodulatory mechanisms may shape associative memory plasticity and the functional organization of neurocognitive processes by affecting the fidelity of neuronal signal transmission, which has consequences for the distinctiveness of neurocognitive representations and the efficacy of distributed neural coding.

Brain oscillatory correlates of working memory constraints.

It has been claimed that the coordination of neuronal oscillations differing in frequency is relevant for cognition. However, the validity of this claim has scarcely been investigated. Recent studies revealed that cross-frequency phase coupling and modulations of alpha-power dissociate between retention of relevant and suppression of irrelevant information in visual working memory (WM). We summarize these important results, and discuss possible implications for understanding the neural mechanisms of WM constraints.

Adult age differences in memory for name–face associations: The effects of intentional and incidental learning

Previous studies have indicated that older adults have a special deficit in the encoding and retrieval of associations. The current study assessed this deficit using ecologically valid name–face pairs. In two experiments, younger and older participants learned a series of name–face pairs under intentional and incidental learning instructions, respectively, and were then tested for their recognition of the faces, the names, and the associations between the names and faces. Under incidental encoding conditions older adults’ performance was uniformly lower than younger adults in all three tests, indicating age-related impairments in episodic memory representations. An age-related deficit specific to associations was found under intentional but not under incidental learning conditions, highlighting the importance of strategic associative processes and their decline in older adults. Separate analyses of hits and false alarms indicate that older adults’ associative deficit originated from high false alarm rates in the associative test. Older adults’ high false alarm rates potentially reflect their reduced ability to recollect the study-phase name–face pairs in the presence of intact familiarity with individual names and faces.

Contralateral Delay Activity Reveals Life-Span Age Differences in Top-Down Modulation of Working Memory Contents

Estimates of working memory (WM) capacity increase in children, peak in young adulthood, and decline thereafter. Despite this symmetry, the mechanisms causing capacity increments in childhood may differ from those causing decline in old age. The contralateral delay activity (CDA) of the electroencephalogram, an event-related difference wave with a posterior scalp distribution, has been suggested as a neural marker of WM capacity. Here, we examine 22 children (10-12 years), 12 younger adults (20-25 years), and 22 older adults (70-75 years) in a cued change detection paradigm. Load levels and presentation times were varied within subjects. Behaviorally, we observed the expected life-span peak in younger adults and better performance with longer presentation times. With short presentation times, task load increased CDA amplitude and decreased behavioral performance in younger adults. Both effects were less pronounced in older adults. Children showed a unique pattern: Their behavioral load effects were as strong as those of younger adults, but their CDA was unaffected by load. With long presentation times, task load modulated the CDA in children and older adults but not in younger adults. These findings suggest that age-related differences in CDA reflect changes in the top-down control over WM representations.

The influence of prior knowledge on memory: a developmental cognitive neuroscience perspective

Across ontogenetic development, individuals gather manifold experiences during which they detect regularities in their environment and thereby accumulate knowledge. This knowledge is used to guide behavior, make predictions, and acquire further new knowledge. In this review, we discuss the influence of prior knowledge on memory from both the psychology and the emerging cognitive neuroscience literature and provide a developmental perspective on this topic. Recent neuroscience findings point to a prominent role of the medial prefrontal cortex (mPFC) and of the hippocampus (HC) in the emergence of prior knowledge and in its application during the processes of successful memory encoding, consolidation, and retrieval. We take the lateral PFC into consideration as well and discuss changes in both medial and lateral PFC and HC across development and postulate how these may be related to the development of the use of prior knowledge for remembering. For future direction, we argue that, to measure age differential effects of prior knowledge on memory, it is necessary to distinguish the availability of prior knowledge from its accessibility and use.

Amplitude modulations and inter-trial phase stability of alpha-oscillations differentially reflect working memory constraints across the lifespan

Working memory (WM) capacity increases across childhood, peaks in young adulthood, and declines thereafter. Developmental and aging theories suggest that deficient inhibitory control processes in children and older adults may underlie the lower performance relative to younger adults. Recently, oscillatory alpha power (7-13 Hz) of the electroencephalogram (EEG) has been suggested as a neural marker of inhibition processes contributing to WM performance (Sauseng et al., 2009). We examined 20 children (10-13 years), 12 younger adults (20-26 years), and 20 older adults (70-76 years) in a cued change-detection paradigm. Behaviorally, we observed the expected lifespan peak in younger adults. EEG alpha power was generally reduced in older adults compared to children and younger adults. In line with previous research, hemispheric differences in alpha power related to attention and WM processes during the retention interval increased with load in younger adults. In children and older adults, lateralized alpha power increased from low to medium load conditions, but decreased for high load conditions. Furthermore, older adults showed higher inter-trial phase stability shortly after stimulus onset compared to children and younger adults. Our results show that inhibitory control processes as indexed by local alpha power modulations can be observed in children and older adults but seem to break down when WM load is high. In addition, older adults are more entrained by external stimulation what may increase a need for inhibitory control during later processing. We conclude that differences in inhibitory control processes and information uptake as reflected in amplitude modulations and inter-trial phase stability of alpha rhythms interactively determine WM constraints across the lifespan.

Committing memory errors with high confidence: Older adults do but children don't

We investigated lifespan differences of confidence calibration in episodic memory, particularly the susceptibility to high-confidence errors within samples of children, teenagers, younger adults, and older adults. Using an associative recognition memory paradigm, we drew a direct link between older adults’ associative deficit and high-confidence errors. We predicted that only older adults would show high-confidence error even though their memory performance was at a similar level to that of children. Participants of all ages showed higher confidence following correct responses compared to incorrect responses, demonstrating the ability to calibrate subjective confidence in relation to memory accuracy. However, older adults were disproportionately more likely to indicate high confidence following erroneously remembered word pairs than participants of the other three age groups. Results are discussed in relation to the misrecollection account of high-confidence errors and ageing-related decline in hippocampus-dependent episodic memory functions.