Julie M. Bugg

Exercise and Alzheimer's Disease Biomarkers in Cognitively Normal Older Adults

In addition to the increasingly recognized role of physical exercise in maintaining cognition, exercise may influence Alzheimers disease (AD) pathology, as transgenic mouse studies show lowered levels of AD pathology in exercise groups. The objective of this study was to elucidate the association between exercise and AD pathology in humans using Pittsburgh compound‐B (PIB), amyloid‐β (Aβ)42, tau, and phosphorylated tau (ptau)181 biomarkers.

Exercise moderates age-related atrophy of the medial temporal lobe

Regional deterioration of brain structure is a typical feature of aging, but emerging evidence suggests that exercise may mitigate the decline. The purpose of the present investigation was to examine the moderating influence of exercise engagement on cross-sectional estimates of age-related brain atrophy at both global and regional levels. Estimates of exercise engagement over the past 10 years and MRI-based measures of global (gray and white) and regional volumes were obtained in a sample of 52 healthy older adults aged 55-79. Volume estimates were obtained in prefrontal, parietal, temporal, occipital, neostriatal, and medial temporal regions. Higher levels of exercise engagement were related to larger superior frontal volumes. Most critically, exercise engagement selectively moderated age-related medial temporal lobe atrophy. Specifically, significant age-related atrophy was observed for older adults who engaged in low levels of exercise, but not for those who engaged in high levels of exercise. This novel finding extends support for the efficacy of exercise to the potential maintenance of medial temporal lobe integrity in older adults.

In Support of a Distinction between Voluntary and Stimulus-Driven Control: A Review of the Literature on Proportion Congruent Effects

Cognitive control is by now a large umbrella term referring collectively to multiple processes that plan and coordinate actions to meet task goals. A common feature of paradigms that engage cognitive control is the task requirement to select relevant information despite a habitual tendency (or bias) to select goal-irrelevant information. At least since the 1970s, researchers have employed proportion congruent (PC) manipulations to experimentally establish selection biases and evaluate the mechanisms used to control attention. PC manipulations vary the frequency with which irrelevant information conflicts (i.e., is incongruent) with relevant information. The purpose of this review is to summarize the growing body of literature on PC effects across selective attention paradigms, beginning first with Stroop, and then describing parallel effects in flanker and task-switching paradigms. The review chronologically tracks the expansion of the PC manipulation from its initial implementation at the list-wide level, to more recent implementations at the item-specific and context-specific levels. An important theoretical aim is demonstrating that PC effects at different levels (e.g., list-wide vs. item or context-specific) support a distinction between voluntary forms of cognitive control, which operate based on anticipatory information, and relatively automatic or reflexive forms of cognitive control, which are rapidly triggered by the processing of particular stimuli or stimulus features. A further aim is to highlight those PC manipulations that allow researchers to dissociate stimulus-driven control from other stimulus-driven processes (e.g., S-R responding; episodic retrieval). We conclude by discussing the utility of PC manipulations for exploring the distinction between voluntary control and stimulus-driven control in other relevant paradigms.

Multiple levels of control in the Stroop task

Multiple levels of control may be used in service of reducing Stroop interference. One is list-wide, whereby interference is reduced strategically in lists that include disproportionately more incongruent trials. A second, item-specific control is observed when proportion congruence is manipulated at the level of items. Item-specific control reduces interference for mostly incongruent relative to mostly congruent items. First, we show that item-specific control may drive both list-wide and item-specific proportion congruence effects (Experiment 1). We then show that item-specific control affects Stroop interference similarly when a single feature (a word) as opposed to a feature combination (a word 1 font type) signals proportion congruence (Experiment 2). Although this suggests that font type offers little advantage for controlling Stroop interference beyond the word, a novel, font-specific proportion congruence effect is observed in Experiment 3, indicating that font type can be used to control interference. These findings support the idea that multiple levels of control are used in reducing Stroop interference.

Can the survival recall advantage be explained by basic memory processes

Nairne, Thompson, and Pandeirada (2007) demonstrated a striking phenomenon: Words rated for relevance to a grasslands survival scenario were remembered better than identical words encoded under other deep processing conditions. Having replicated this effect using a novel set of words (Experiment 1), we contrasted the schematic processing and evolutionary accounts of the recall advantage (Experiment 2). Inconsistent with the schematic processing account, the grasslands survival scenario produced better recall than did a city survival scenario requiring comparable schematic processing. Recall in the grasslands scenario was unaffected by a self-reference manipulation. The findings are consistent with an evolutionary account that attributes the recall advantage to adaptive memory biases.

Instability in memory phenomena: A common puzzle and a unifying explanation

In mixed lists, stable free recall advantages are observed for encoding conditions that are unusual, bizarre, or attract extensive individual item elaboration relative to more common encoding conditions; but this recall advantage is often eliminated or reversed in pure lists. We attempt to explain this ubiquitous memory puzzle with an item-order account that assumes that (1) free recall of unrelated lists depends on order and item information; (2) unusual items attract greater individual item-processing but disrupt order encoding regardless of list composition; and (3) list composition determines differences in order encoding across unusual and common items. We show that the item-order account provides a unifying explanation of five memory phenomena for which the requisite data exist. The account also successfully anticipates pure-list reversals, in which the standard mixed-list recall pattern is obtained in pure, structured lists, a finding that competing accounts cannot handle. Extending the item-order account to other “established” recall phenomena may prove fruitful.

Why It Is Too Early to Lose Control in Accounts of Item-Specific Proportion Congruency Effects.

The item-specific proportion congruency (ISPC) effect is the finding of attenuated interference for mostly incongruent as compared to mostly congruent items. A debate in the Stroop literature concerns the mechanisms underlying this effect. Noting a confound between proportion congruency and contingency, Schmidt and Besner (2008) suggested that ISPC effects are entirely contingency based. We introduce a broader theoretical analysis that points to the contribution of both contingency and item-specific control mechanisms. Our analysis highlights that proportion congruency is not confounded with contingency when the relevant dimension functions as the ISPC signal, and predicts that evidence of item-specific control should be obtained by shifting the signal from the irrelevant to the relevant dimension. We examine this prediction in a picture-word Stroop paradigm. When the relevant dimension functions as the ISPC signal (Experiments 1 and 2), evidence of control is obtained. When the irrelevant dimension functions as the ISPC signal (Experiment 3), contingencies can account for the ISPC effect. These patterns support our theoretical analysis, challenge a pure contingency account, and favor the inclusion of control in accounts of ISPC effects.

Age Differences in Stroop Interference: Contributions of General Slowing and Task-Specific Deficits

ABSTRACT This study examined the contributions of general slowing and task-specific deficits to age-related changes in Stroop interference. Nine hundred thirty-eight participants aged 20 to 89 years completed an abbreviated Stroop color-naming task and a subset of 281 participants also completed card-sorting, simple reaction time, and choice reaction time tasks. Age-related increases in incongruent color-naming latency and card-sorting perseverative errors were observed. Hierarchical regression analyses showed that the processing speed measures accounted for significant variance on both dependent measures, but that there was also a significant residual effect of age. An additional regression analysis showed that some of the variance in incongruent color-naming, after controlling for processing speed, was shared with the variance in perseverative errors. Overall, findings suggest that the age difference in Stroop interference is partially attributable to general slowing, but is also attributable to age-related changes in task-specific processes such as inhibitory control.

Structural Correlates of Prospective Memory

Prospective memory (PM) includes the encoding and maintenance of an intention, and the retrieval and execution of this intention at the proper moment in the future. The present study expands upon previous behavioral, electrophysiological, and functional work by examining the association between grey matter volume and PM. Estimates of grey matter volume in theoretically relevant regions of interest (prefrontal, parietal, and medial temporal) were obtained in conjunction with performance on two PM tasks in a sample of 39 cognitively normal and very mildly demented older adults. The first PM task, termed focal in the literature, is supported by spontaneous retrieval of the PM intention whereas the second, termed non-focal, relies on strategic monitoring processes for successful intention retrieval. A positive relationship was observed between medial temporal volume and accuracy on the focal PM task. An examination of medial temporal lobe subregions revealed that this relationship was strongest for the hippocampus, which is considered to support spontaneous memory retrieval. There were no significant structure-behavior associations for the non-focal PM task. These novel results confirm a relationship between behavior and underlying brain structure proposed by the multiprocess theory of PM, and extend findings on cognitive correlates of medial temporal lobe integrity.

Prospective memory and aging: preserved spontaneous retrieval, but impaired deactivation, in older adults

Prospective remembering is partially supported by cue-driven spontaneous retrieval processes. We investigated spontaneous retrieval processes in younger and older adults by presenting prospective memory target cues during a lexical decision task following instructions that the prospective memory task was finished. Spontaneous retrieval was inferred from slowed lexical decision responses to target cues (i.e., intention interference). When the intention was finished, younger adults efficiently deactivated their intention, but the older adults continued to retrieve their intentions. Levels of inhibitory functioning were negatively associated with intention interference in the older adult group, but not in the younger adult group. These results indicate that normal aging might not compromise spontaneous retrieval processes but that the ability to deactivate completed intentions is impaired.