Julia Spaniol

Event-related fMRI studies of episodic encoding and retrieval: Meta-analyses using activation likelihood estimation

The recent surge in event-related fMRI studies of episodic memory has generated a wealth of information about the neural correlates of encoding and retrieval processes. However, interpretation of individual studies is hampered by methodological differences, and by the fact that sample sizes are typically small. We submitted results from studies of episodic memory in healthy young adults, published between 1998 and 2007, to a voxel-wise quantitative meta-analysis using activation likelihood estimation [Laird, A. R., McMillan, K. M., Lancaster, J. L., Kochunov, P., Turkeltaub, P. E., & Pardo, J. V., et al. (2005). A comparison of label-based review and ALE meta-analysis in the stroop task. Human Brain Mapping, 25, 6-21]. We conducted separate meta-analyses for four contrasts of interest: episodic encoding success as measured in the subsequent-memory paradigm (subsequent Hit vs. Miss), episodic retrieval success (Hit vs. Correct Rejection), objective recollection (e.g., Source Hit vs. Item Hit), and subjective recollection (e.g., Remember vs. Know). Concordance maps revealed significant cross-study overlap for each contrast. In each case, the left hemisphere showed greater concordance than the right hemisphere. Both encoding and retrieval success were associated with activation in medial-temporal, prefrontal, and parietal regions. Left ventrolateral prefrontal cortex (PFC) and medial-temporal regions were more strongly involved in encoding, whereas left superior parietal and dorsolateral and anterior PFC regions were more strongly involved in retrieval. Objective recollection was associated with activation in multiple PFC regions, as well as multiple posterior parietal and medial-temporal areas, but not hippocampus. Subjective recollection, in contrast, showed left hippocampal involvement. In summary, these results identify broadly consistent activation patterns associated with episodic encoding and retrieval, and subjective and objective recollection, but also subtle differences among these processes.

Aging and emotional memory: cognitive mechanisms underlying the positivity effect.

Younger adults tend to remember negative information better than positive or neutral information (negativity bias). The negativity bias is reduced in aging, with older adults occasionally exhibiting superior memory for positive, as opposed to negative or neutral, information (positivity bias). Two experiments with younger (N=24 in Experiment 1, N=25 in Experiment 2; age range: 18-35 years) and older adults (N=24 in both experiments; age range: 60-85 years) investigated the cognitive mechanisms responsible for age-related differences in recognition memory for emotional information. Results from diffusion model analyses (R. Ratcliff, 1978) indicated that the effects of valence on response bias were similar in both age groups but that Age x Valence interactions emerged in memory retrieval. Specifically, older adults experienced greater overall familiarity for positive items than younger adults. We interpret this finding in terms of an age-related increase in the accessibility of positive information in long-term memory.

Aging and the neural correlates of source memory: over-recruitment and functional reorganization

Behavioral evidence suggests that memory for context (i.e., source memory) is more vulnerable to age-related decline than item memory. It is not clear, however, whether this pattern reflects a specific age-related deficit in context memory or a more general effect of task difficulty. In the present study, we used event-related functional magnetic resonance imaging (fMRI) with healthy younger and older adults to dissociate the effects of age, task (item vs. source memory), and task difficulty (1 vs. 2 study presentations) on patterns of blood oxygen level-dependent (BOLD) signal changes during memory retrieval. Behavioral performance was similar in both age groups, but was sensitive to task and difficulty (item > source; easy > difficult). Data-driven multivariate analyses revealed age differences consistent with age-related overrecruitment of frontoparietal regions during difficult task conditions, and age-related functional reorganization in bilateral frontal and right-lateralized posterior regions that were sensitive to difficulty in younger adults, but to task (i.e., context demand) in older adults. These findings support the hypothesis of a specific context memory deficit in older adults.

Reward-Enhanced Memory in Younger and Older Adults

OBJECTIVES We investigated how the anticipation of remote monetary reward modulates intentional episodic memory formation in younger and older adults. On the basis of prior findings of preserved reward-cognition interactions in aging, we predicted that reward anticipation would be associated with enhanced memory in both younger and older adults. On the basis of previous demonstrations of a time-dependent effect of reward anticipation on memory, we expected the memory enhancement to increase with study-test delay. METHOD In Experiment 1, younger and older participants encoded a series of picture stimuli associated with high- or low-reward values. At test (24-hr postencoding), recognition hits resulted in either high or low monetary rewards, whereas false alarms were penalized to discourage guessing. Experiment 2 was similar to Experiment 1, but the study-test delay was manipulated within subjects (immediate vs 24hr). RESULTS In Experiment 1, younger and older adults showed enhanced recognition for high-reward pictures compared with low-reward pictures. Experiment 2 replicated this finding and additionally showed that the effect did not extend to immediate recognition. DISCUSSION The current findings provide support for a time-dependent mechanism of reward-based memory enhancement. They also suggest that aging leaves intact the positive influence of reward anticipation on intentional long-term memory formation.

Neural responses to monetary incentives in younger and older adults

Reward anticipation is associated with activity in the dopaminergic midbrain as well as the ventral striatum, amygdala, and medial prefrontal cortex. Dopaminergic neuromodulation declines with age, suggesting that incentive processing should also undergo age-related change. However, the literature is mixed, perhaps reflecting variation in the degree to which tasks made demands on learning and memory. Furthermore, the emphasis has been on the reward network, with few studies addressing reward-related activations in other brain regions. In the current study, 16 younger adults (mean age: 25.4) and 15 older adults (mean age: 69.0) underwent fMRI while completing a monetary incentive delay task. This task allowed the separate assessment of responses to gain and loss incentive cues while minimizing memory demands. We assessed incentive-related activations using mean-centered Partial Least Squares, a data-driven multivariate technique optimal for identifying spatiotemporal whole-brain activation patterns associated with variation in task conditions. The analyses yielded two significant latent variables representing distinct incentive-related activation patterns. The first pattern showed robust activation of the reward network and was not modulated by age. The second pattern, peaking ~10s after cue onset, showed reduced deactivation of default-network regions, and increased activation of prefrontal cognitive-control regions in older adults, compared with younger adults. Neither pattern was modulated by incentive valence. Overall, these findings suggest that aging may not affect primary motivational signaling in the reward network, but may rather be associated with alterations in incentive-driven modulation of cortical networks that influence multiple cognitive domains. This article is part of a Special Issue entitled Memory & Aging.

Ventromedial Prefrontal Damage and Memory for Context: Perceptual Versus Semantic Features

Memory for context is known to rely on episodic binding and strategic retrieval processes. It is unclear, however, whether memory for different contextual features taps the same cognitive and neural mechanisms. Here, the authors compare memory for a perceptual feature (i.e., the format in which an item had been presented) and for a semantic feature (i.e., the concept with which an item had been paired) in 13 patients with lesions in ventromedial prefrontal cortex, including patients with and without confabulation, and 13 healthy controls. Participants studied picture-word pairs and received an old-new recognition test that included intact pairs, rearranged pairs, format pairs (studied pairs in which the picture-word format of each item was switched), old-new pairs, and new-new pairs. Hit rates for intact pairs were similar for all participant groups. Compared with controls, patients, especially those with confabulation, had higher false-alarm rates for format pairs but comparable false-alarm rates for rearranged pairs. The authors propose that distinct monitoring processes are engaged during retrieval of perceptual and semantic context, with only the former crucially dependent on ventromedial prefrontal cortex.

Motivational incentives modulate age differences in visual perception.

This study examined whether motivational incentives modulate age-related perceptual deficits. Younger and older adults performed a perceptual discrimination task in which bicolored stimuli had to be classified according to their dominating color. The valent color was associated with either a positive or negative payoff, whereas the neutral color was not associated with a payoff. Effects of incentives on perceptual efficiency and response bias were estimated using the diffusion model (Ratcliff, 1978). Perception of neutral stimuli showed age-related decline, whereas perception of valent stimuli, both positive and negative, showed no age difference. This finding is interpreted in terms of preserved top-down control over the allocation of perceptual processing resources in healthy aging.

A Diffusion Model Analysis of Decision Biases Affecting Delayed Recognition of Emotional Stimuli.

Previous empirical work suggests that emotion can influence accuracy and cognitive biases underlying recognition memory, depending on the experimental conditions. The current study examines the effects of arousal and valence on delayed recognition memory using the diffusion model, which allows the separation of two decision biases thought to underlie memory: response bias and memory bias. Memory bias has not been given much attention in the literature but can provide insight into the retrieval dynamics of emotion modulated memory. Participants viewed emotional pictorial stimuli; half were given a recognition test 1-day later and the other half 7-days later. Analyses revealed that emotional valence generally evokes liberal responding, whereas high arousal evokes liberal responding only at a short retention interval. The memory bias analyses indicated that participants experienced greater familiarity with high-arousal compared to low-arousal items and this pattern became more pronounced as study-test lag increased; positive items evoke greater familiarity compared to negative and this pattern remained stable across retention interval. The findings provide insight into the separate contributions of valence and arousal to the cognitive mechanisms underlying delayed emotion modulated memory.

Age differences in the Attention Network Test: Evidence from behavior and event-related potentials

The Attention Network Test (ANT) is widely used to capture group and individual differences in selective attention. Prior behavioral studies with younger and older adults have yielded mixed findings with respect to age differences in three putative attention networks (alerting, orienting, and executive control). To overcome the limitations of behavioral data, the current study combined behavioral and electrophysiological measures. Twenty-four healthy younger adults (aged 18-29years) and 24 healthy older adults (aged 60-76years) completed the ANT while EEG data were recorded. Behaviorally, older adults showed reduced alerting, but did not differ from younger adults in orienting or executive control. Electrophysiological components related to alerting and orienting (P1, N1, and CNV) were similar in both age groups, whereas components related to executive control (N2 and P3) showed age-related differences. Together these results suggest that comparisons of network effects between age groups using behavioral data alone may not offer a complete picture of age differences in selective attention, especially for alerting and executive control networks.

Aging, Culture, and Memory for Socially Meaningful Item-Context Associations: An East-West Cross-Cultural Comparison Study

Research suggests that people in Eastern interdependent cultures process information more holistically and attend more to contextual information than do people in Western independent cultures. The current study examined the effects of culture and age on memory for socially meaningful item-context associations in 71 Canadians of Western European descent (35 young and 36 older) and 72 native Chinese citizens (36 young and 36 older). All participants completed two blocks of context memory tasks. During encoding, participants rated pictures of familiar objects. In one block, objects were rated either for their meaningfulness in the independent living context or their typicality in daily life. In the other block, objects were rated for their meaningfulness in the context of fostering relationships with others or for their typicality in daily life. The encoding in each block was followed by a recognition test in which participants identified pictures and their associated contexts. The results showed that Chinese outperformed Canadians in context memory, though both culture groups showed similar age-related deficits in item and context memory. The results suggest that Chinese are at an advantage in memory for socially meaningful item-context associations, an advantage that continues from young adulthood into old age.