Better together: novel methods for measuring and modeling development of executive function diversity while accounting for unity

INTRODUCTION

Executive functions (EFs) are linked to positive outcomes across the lifespan. Yet, methodological challenges have prevented precise understanding of the developmental trajectory of their organization.

METHODS

We introduce novel methods to address challenges for both measuring and modeling EFs using an accelerated longitudinal design with a large, diverse sample of students in middle childhood (N = 1,286; ages 8 to 14). We used eight adaptive assessments hypothesized to measure three EFs, working memory, context monitoring, and interference resolution. We deployed adaptive assessments to equate EF challenge across ages and a data-driven, network analytic approach to reveal the evolving diversity of EFs while simultaneously accounting for their unity.

RESULTS AND DISCUSSION

Using this methodological paradigm shift brought new precision and clarity to the development of these EFs, showing these eight tasks are organized into three stable components by age 10, but refinement of composition of these components continues through at least age 14.

Testing the whole number interference hypothesis: Contributions of inhibitory control and whole number knowledge to fraction understanding

The present study tests two predictions stemming from the hypothesis that a source of difficulty with rational numbers is interference from whole number magnitude knowledge. First, inhibitory control should be an independent predictor of fraction understanding, even after controlling for working memory. Second, if the source of interference is whole number knowledge, then it should hinder fraction understanding. These predictions were tested in a racially and socioeconomically diverse sample of U.S. children (N = 765; 337 female) in Grades 3 (ages 8-9), 5 (ages 10-11), and 7 (ages 12-13) who completed a battery of computerized tests. The fraction comparison task included problems with both shared components (e.g., 3/5 > 2/5) and distinct components (e.g., 2/3 > 5/9), and problems that were congruent (e.g., 5/6 > 3/4) and incongruent (e.g., 3/4 > 5/7) with whole number knowledge. Inhibitory control predicted fraction comparison performance over and above working memory across component and congruency types. Whole number knowledge did not hinder performance and instead positively predicted performance for fractions with shared components. These results highlight a role for inhibitory control in rational number understanding and suggest that its contribution may be distinct from inhibiting whole number magnitude knowledge. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Groupitizing reflects conceptual developments in math cognition and inequities in math achievement from childhood through adolescence

Understanding the cognitive processes central to mathematical development is crucial to addressing systemic inequities in math achievement. We investigate the "Groupitizing" ability in 1209 third to eighth graders (mean age at first timepoint = 10.48, 586 girls, 39.16% Asian, 28.88% Hispanic/Latino, 18.51% White), a process that captures the ability to use grouping cues to access the exact value of a set. Groupitizing improves each year from late childhood to early adolescence (d = 3.29), is a central predictor of math achievement (beta weight = .30), is linked to conceptual processes in mathematics (minimum d = 0.69), and helps explain the dynamic between the ongoing development of non-symbolic number concepts, systemic educational inequities in school associated with SES, and mathematics achievement (minimum beta weight = .11) in ways that explicit symbolic measures may miss.

Relational thinking: An overlooked component of executive functioning

Relational thinking, the ability to represent abstract, generalizable relations, is a core component of reasoning and human cognition. Relational thinking contributes to fluid reasoning and academic achievement, particularly in the domain of math. However, due to the complex nature of many fluid reasoning tasks, it has been difficult to determine the degree to which relational thinking has a separable role from the cognitive processes collectively known as executive functions (EFs). Here, we used a simplified reasoning task to better understand how relational thinking contributes to math achievement in a large, diverse sample of elementary and middle school students (N = 942). Students also performed a set of ten adaptive EF assessments, as well as tests of math fluency and fraction magnitude comparison. We found that relational thinking was significantly correlated with each of the three EF composite scores previously derived from this dataset, albeit no more strongly than they were with each other. Further, relational thinking predicted unique variance in students' math fluency and fraction magnitude comparison scores over and above the three EF composites. Thus, we propose that relational thinking be considered an EF in its own right as one of the core, mid-level cognitive abilities that supports cognition and goal-directed behavior. RESEARCH HIGHLIGHTS: Relational thinking, the process of identifying and integrating relations, develops over childhood and is central to reasoning. We collected data from nearly 1000 elementary and middle schoolers on a test of relational thinking, ten standard executive function tasks, and two math tests. Relational thinking predicts unique variance in math achievement not accounted for by canonical EFs throughout middle childhood. We propose that relational thinking should be conceptualized as a core executive function that supports cognitive development and learning.

Linking inhibitory control to math achievement via comparison of conflicting decimal numbers

The relationship between executive functions (EF) and academic achievement is well-established, but leveraging this insight to improve educational outcomes remains elusive. Here, we propose a framework for relating the role of specific EF on specific precursor skills that support later academic learning. Starting from the premise that executive functions contribute to general math skills both directly - supporting the execution of problem solving strategies - and indirectly - supporting the acquisition of precursor mathematical content, we hypothesize that the contribution of domain-general EF capacities to precursor skills that support later learning can help explain relations between EF and overall math skills. We test this hypothesis by examining whether the contribution of inhibitory control on general math knowledge can be explained by inhibition's contribution to processing rational number pairs that conflict with individual's prior whole number knowledge. In 97 college students (79 female, age = 20.58 years), we collected three measures of EF: working memory (backwards spatial span), inhibition (color-word Stroop) and cognitive flexibility (task switching), and timed and untimed standardized measures of math achievement. Our target precursor skill was a decimals comparison task where correct responses were inconsistent with prior whole number knowledge (e.g., 0.27 vs. 0.9). Participants performed worse on these trials relative to the consistent decimals pairs (e.g., 0.2 vs. 0.87). Individual differences in the Stroop task predicted performance on inconsistent decimal comparisons, which in turn predicted general math achievement. With respect to relating inhibitory control to math achievement, Stroop performance was an independent predictor of achievement after accounting for age, working memory and cognitive flexibility, but decimal performance mediated this relationship. Finally, we found inconsistent decimals performance mediated the relationship of inhibition with rational number performance, but not other advanced mathematical concepts. These results pinpoint the specific contribution of inhibitory control to rational number understanding, and more broadly are consistent with the hypothesis that acquisition of foundational mathematical content can explain the relationships between executive functions and academic outcomes, making them promising targets for intervention.

Memory failure predicted by attention lapsing and media multitasking

With the explosion of digital media and technologies, scholars, educators and the public have become increasingly vocal about the role that an 'attention economy' has in our lives1. The rise of the current digital culture coincides with longstanding scientific questions about why humans sometimes remember and sometimes forget, and why some individuals remember better than others2-6. Here we examine whether spontaneous attention lapses-in the moment7-12, across individuals13-15 and as a function of everyday media multitasking16-19-negatively correlate with remembering. Electroencephalography and pupillometry measures of attention20,21 were recorded as eighty young adults (mean age, 21.7 years) performed a goal-directed episodic encoding and retrieval task22. Trait-level sustained attention was further quantified using task-based23 and questionnaire measures24,25. Using trial-to-trial retrieval data, we show that tonic lapses in attention in the moment before remembering, assayed by posterior alpha power and pupil diameter, were correlated with reductions in neural signals of goal coding and memory, along with behavioural forgetting. Independent measures of trait-level attention lapsing mediated the relationship between neural assays of lapsing and memory performance, and between media multitasking and memory. Attention lapses partially account for why we remember or forget in the moment, and why some individuals remember better than others. Heavier media multitasking is associated with a propensity to have attention lapses and forget.

Focus on the Breath: Brain Decoding Reveals Internal States of Attention During Meditation

Meditation practices are often used to cultivate interoception or internally-oriented attention to bodily sensations, which may improve health via cognitive and emotional regulation of bodily signals. However, it remains unclear how meditation impacts internal attention (IA) states due to lack of measurement tools that can objectively assess mental states during meditation practice itself, and produce time estimates of internal focus at individual or group levels. To address these measurement gaps, we tested the feasibility of applying multi-voxel pattern analysis (MVPA) to single-subject fMRI data to: (1) learn and recognize internal attentional states relevant for meditation during a directed IA task; and (2) decode or estimate the presence of those IA states during an independent meditation session. Within a mixed sample of experienced meditators and novice controls (N = 16), we first used MVPA to develop single-subject brain classifiers for five modes of attention during an IA task in which subjects were specifically instructed to engage in one of five states [i.e., meditation-related states: breath attention, mind wandering (MW), and self-referential processing, and control states: attention to feet and sounds]. Using standard cross-validation procedures, MVPA classifiers were trained in five of six IA blocks for each subject, and predictive accuracy was tested on the independent sixth block (iterated until all volumes were tested, N = 2,160). Across participants, all five IA states were significantly recognized well above chance (>41% vs. 20% chance). At the individual level, IA states were recognized in most participants (87.5%), suggesting that recognition of IA neural patterns may be generalizable for most participants, particularly experienced meditators. Next, for those who showed accurate IA neural patterns, the originally trained classifiers were applied to a separate meditation run (10-min) to make an inference about the percentage time engaged in each IA state (breath attention, MW, or self-referential processing). Preliminary group-level analyses demonstrated that during meditation practice, participants spent more time attending to breath compared to MW or self-referential processing. This paradigm established the feasibility of using MVPA classifiers to objectively assess mental states during meditation at the participant level, which holds promise for improved measurement of internal attention states cultivated by meditation.

Differential Medial Temporal Lobe and Parietal Cortical Contributions to Real-world Autobiographical Episodic and Autobiographical Semantic Memory

Autobiographical remembering can depend on two forms of memory: episodic (event) memory and autobiographical semantic memory (remembering personally relevant semantic knowledge, independent of recalling a specific experience). There is debate about the degree to which the neural signals that support episodic recollection relate to or build upon autobiographical semantic remembering. Pooling data from two fMRI studies of memory for real-world personal events, we investigated whether medial temporal lobe (MTL) and parietal subregions contribute to autobiographical episodic and semantic remembering. During scanning, participants made memory judgments about photograph sequences depicting past events from their life or from others’ lives, and indicated whether memory was based on episodic or semantic knowledge. Results revealed several distinct functional patterns: activity in most MTL subregions was selectively associated with autobiographical episodic memory; the hippocampal tail, superior parietal lobule, and intraparietal sulcus were similarly engaged when memory was based on retrieval of an autobiographical episode or autobiographical semantic knowledge; and angular gyrus demonstrated a graded pattern, with activity declining from autobiographical recollection to autobiographical semantic remembering to correct rejections of novel events. Collectively, our data offer insights into MTL and parietal cortex functional organization, and elucidate circuitry that supports different forms of real-world autobiographical memory.

Media Multitasking and Cognitive, Psychological, Neural, and Learning Differences

American youth spend more time with media than any other waking activity: an average of 7.5 hours per day, every day. On average, 29% of that time is spent juggling multiple media streams simultaneously (ie, media multitasking). This phenomenon is not limited to American youth but is paralleled across the globe. Given that a large number of media multitaskers (MMTs) are children and young adults whose brains are still developing, there is great urgency to understand the neurocognitive profiles of MMTs. It is critical to understand the relation between the relevant cognitive domains and underlying neural structure and function. Of equal importance is understanding the types of information processing that are necessary in 21st century learning environments. The present review surveys the growing body of evidence demonstrating that heavy MMTs show differences in cognition (eg, poorer memory), psychosocial behavior (eg, increased impulsivity), and neural structure (eg, reduced volume in anterior cingulate cortex). Furthermore, research indicates that multitasking with media during learning (in class or at home) can negatively affect academic outcomes. Until the direction of causality is understood (whether media multitasking causes such behavioral and neural differences or whether individuals with such differences tend to multitask with media more often), the data suggest that engagement with concurrent media streams should be thoughtfully considered. Findings from such research promise to inform policy and practice on an increasingly urgent societal issue while significantly advancing our understanding of the intersections between cognitive, psychosocial, neural, and academic factors.

Increased functional connectivity between dorsal posterior parietal and ventral occipitotemporal cortex during uncertain memory decisions

Retrieval of episodic memories is a multi-component act that relies on numerous operations ranging from processing the retrieval cue, evaluating retrieved information, and selecting the appropriate response given the demands of the task. Motivated by a rich functional neuroimaging literature, recent theorizing about various computations at retrieval has focused on the role of posterior parietal cortex (PPC). In a potentially promising line of research, recent neuroimaging findings suggest that different subregions of dorsal PPC respond distinctly to different aspects of retrieval decisions, suggesting that better understanding of their contributions might shed light on the component processes of retrieval. In an attempt to understand the basic operations performed by dorsal PPC, we used functional MRI and functional connectivity analyses to examine how activation in, and connectivity between, dorsal PPC and ventral temporal regions representing retrieval cues varies as a function of retrieval decision uncertainty. Specifically, participants made a five-point recognition confidence judgment for a series of old and new visually presented words. Consistent with prior studies, memory-related activity patterns dissociated across left dorsal PPC subregions, with activity in the lateral IPS tracking the degree to which participants perceived an item to be old, whereas activity in the SPL increased as a function of decision uncertainty. Importantly, whole-brain functional connectivity analyses further revealed that SPL activity was more strongly correlated with that in the visual word-form area during uncertain relative to certain decisions. These data suggest that the involvement of SPL during episodic retrieval reflects, at least in part, the processing of the retrieval cue, perhaps in service of attempts to increase the mnemonic evidence elicited by the cue.

Functional heterogeneity in posterior parietal cortex across attention and episodic memory retrieval

While attention is critical for event memory, debate has arisen regarding the extent to which posterior parietal cortex (PPC) activation during episodic retrieval reflects engagement of PPC-mediated mechanisms of attention. Here, we directly examined the relationship between attention and memory, within and across subjects, using functional magnetic resonance imaging attention-mapping and episodic retrieval paradigms. During retrieval, 4 functionally dissociable PPC regions were identified. Specifically, 2 PPC regions positively tracked retrieval outcomes: lateral intraparietal sulcus (latIPS) indexed graded item memory strength, whereas angular gyrus (AnG) tracked recollection. By contrast, 2 other PPC regions demonstrated nonmonotonic relationships with retrieval: superior parietal lobule (SPL) tracked retrieval reaction time, consistent with a graded engagement of top-down attention, whereas temporoparietal junction displayed a complex pattern of below-baseline retrieval activity, perhaps reflecting disengagement of bottom-up attention. Analyses of retrieval effects in PPC topographic spatial attention maps (IPS0-IPS5; SPL1) revealed that IPS5 and SPL1 exhibited a nonmonotonic relationship with retrieval outcomes resembling that in the SPL region, further suggesting that SPL activation during retrieval reflects top-down attention. While demands on PPC attention mechanisms vary during retrieval attempts, the present functional parcellation of PPC indicates that 2 additional mechanisms (mediated by latIPS and AnG) positively track retrieval outcomes.

A roadmap to brain mapping: toward a functional map of human parietal cortex

In this issue of Neuron, Nelson and colleagues report a novel parcellation of human lateral parietal cortex based on task-induced response profiles and resting-state functional connectivity. Their findings inform current debates about the contributions of parietal cortex to cognition, including the retrieval of episodic memories.

Dissociation of the neural correlates of visual and auditory contextual encoding

The present study contrasted the neural correlates of encoding item-context associations according to whether the contextual information was visual or auditory. Subjects (N=20) underwent fMRI scanning while studying a series of visually presented pictures, each of which co-occurred with either a visually or an auditorily presented name. The task requirement was to judge whether the name corresponded to the presented object. In a subsequent memory test subjects judged whether test pictures were studied or unstudied and, for items judged as studied, indicated the presentation modality of the associated name. Dissociable cortical regions demonstrating increased activity for visual vs. auditory trials (and vice versa) were identified. A subset of these modality-selective regions also showed modality-selective subsequent source memory effects, that is, enhanced responses on trials associated with correct modality judgments relative to those for which modality or item memory later failed. These findings constitute direct evidence for the proposal that successful encoding of a contextual feature is associated with enhanced activity in the cortical regions engaged during the on-line processing of that feature. In addition, successful encoding of visual objects within auditory contexts was associated with more extensive engagement of the hippocampus and adjacent medial temporal cortex than was the encoding of such objects within visual contexts. This raises the possibility that the encoding of across-modality item-context associations places more demands on the hippocampus than does the encoding of within-modality associations.

Posterior parietal cortex and episodic retrieval: convergent and divergent effects of attention and memory

Functional neuroimaging studies of humans engaged in retrieval from episodic memory have revealed a surprisingly consistent pattern of retrieval-related activity in lateral posterior parietal cortex (PPC). Given the well-established role of lateral PPC in subserving goal-directed and reflexive attention, it has been hypothesized that PPC activation during retrieval reflects the recruitment of parietal attention mechanisms during remembering. Here, we evaluate this hypothesis by considering the anatomical overlap of retrieval and attention effects in lateral PPC. We begin by briefly reviewing the literature implicating dorsal PPC in goal-directed attention and ventral PPC in reflexive attention. We then discuss the pattern of dorsal and ventral PPC activation during episodic retrieval, and conclude with consideration of the degree of anatomical convergence across the two domains. This assessment revealed that predominantly divergent subregions of lateral PPC are engaged during acts of episodic retrieval and during goal-directed and reflexive attention, suggesting that PPC retrieval effects reflect functionally distinct mechanisms from these forms of attention. Although attention must play a role in aspects of retrieval, the data reviewed here suggest that further investigation into the relationship between processes of attention and memory, as well as alternative accounts of PPC contributions to retrieval, is warranted.

Posterior parietal cortex and episodic encoding: insights from fMRI subsequent memory effects and dual-attention theory

The formation of episodic memories--memories for life events--is affected by attention during event processing. A leading neurobiological model of attention posits two separate yet interacting systems that depend on distinct regions in lateral posterior parietal cortex (PPC). From this dual-attention perspective, dorsal PPC is thought to support the goal-directed allocation of attention, whereas ventral PPC is thought to support reflexive orienting to information that automatically captures attention. To advance understanding of how parietal mechanisms may impact event encoding, we review functional MRI studies that document the relationship between lateral PPC activation during encoding and subsequent memory performance (e.g., later remembering or forgetting). This review reveals that (a) encoding-related activity is frequently observed in human lateral PPC, (b) increased activation in dorsal PPC is associated with later memory success, and (c) increased activation in ventral PPC predominantly correlates with later memory failure. From a dual-attention perspective, these findings suggest that allocating goal-directed attention during event processing increases the probability that the event will be remembered later, whereas the capture of reflexive attention during event processing may have negative consequences for event encoding. The prevalence of encoding-related activation in parietal cortex suggests that neurobiological models of episodic memory should consider how parietal-mediated attentional mechanisms regulate encoding.

Effects of study task on the neural correlates of source encoding

The present study investigated whether the neural correlates of source memory vary according to study task. Subjects studied visually presented words in one of two background contexts. In each test, subjects made old/new recognition and source memory judgments. In one study test cycle, study words were subjected to animacy judgments, whereas in another cycle the study task required syllable judgments. Functional magnetic resonance imaging (fMRI) was employed to contrast the neural activity elicited by study words that attracted accurate source judgments on the later memory test, as opposed to words for which source judgments were incorrect or for which source information was unavailable. In both tasks, relative to words for which source memory failed, study words that were later assigned to the correct source elicited enhanced activity in ventral extrastriate cortex. In addition to these common effects of subsequent source memory, additional effects were observed that were selective for each study task. The present findings add weight to the proposal that neural activity supporting successful episodic memory encoding is a reflection of both the online processing engaged by an episode as it is experienced, and the demands imposed by the later retrieval task.

Fractionation of the component processes underlying successful episodic encoding: a combined fMRI and divided-attention study

Considerable evidence suggests that attentional resources are necessary for the encoding of episodic memories, but the nature of the relationship between attention and neural correlates of encoding is unclear. Here we address this question using functional magnetic resonance imaging and a divided-attention paradigm in which competition for different types of attentional resources was manipulated. Fifteen volunteers were scanned while making animacy judgments to visually presented words and concurrently performing one of three tasks on auditorily presented words: male/female voice discrimination (control task), 1-back voice comparison (1-back task), or indoor/outdoor judgment (semantic task). The 1-back and semantic tasks were designed to compete for task-generic and task-specific attentional resources, respectively. Using the "remember/know" procedure, memory for the study words was assessed after 15 min. In the control condition, subsequent memory effects associated with later recollection were identified in the left dorsal inferior frontal gyrus and in the left hippocampus. These effects were differentially attenuated in the two more difficult divided-attention conditions. The effects of divided attention seem, therefore, to reflect impairments due to limitations at both task-generic and task-specific levels. Additionally, each of the two more difficult divided-attention conditions was associated with subsequent memory effects in regions distinct from those showing effects in the control condition. These findings suggest the engagement of alternative encoding processes to those engaged in the control task. The overall pattern of findings suggests that divided attention can impact later memory in different ways, and accordingly, that different attentional resources, including task-generic and task-specific resources, make distinct contributions to successful episodic encoding.

Episodic encoding is more than the sum of its parts: an fMRI investigation of multifeatural contextual encoding

Episodic memories are characterized by their contextual richness, yet little is known about how the various features comprising an episode are brought together in memory. Here we employed fMRI and a multidimensional source memory procedure to investigate processes supporting the mnemonic binding of item and contextual information. Volunteers were scanned while encoding items for which the contextual features (color and location) varied independently, allowing activity elicited at the time of study to be segregated according to whether both, one, or neither feature was successfully retrieved on a later memory test. Activity uniquely associated with successful encoding of both features was identified in the intra-parietal sulcus, a region strongly implicated in the support of attentionally mediated perceptual binding. The findings suggest that the encoding of disparate features of an episode into a common memory representation requires that the features be conjoined in a common perceptual representation when the episode is initially experienced.

Neural correlates of differential retrieval orientation: Sustained and item-related components

Retrieval orientation refers to a cognitive state that biases processing of retrieval cues in service of a specific goal. The present study used a mixed fMRI design to investigate whether adoption of different retrieval orientations - as indexed by differences in the activity elicited by retrieval cues corresponding to unstudied items - is associated with differences in the state-related activity sustained across a block of test trials sharing a common retrieval goal. Subjects studied mixed lists comprising visually presented words and pictures. They then undertook a series of short test blocks in which all test items were visually presented words. The blocks varied according to whether the test items were used to cue retrieval of studied words or studied pictures. In several regions, neural activity elicited by correctly classified new items differed according to whether words or pictures were the targeted material. The loci of these effects suggest that one factor driving differential cue processing is modulation of the degree of overlap between cue and targeted memory representations. In addition to these item-related effects, neural activity sustained throughout the test blocks also differed according to the nature of the targeted material. These findings indicate that the adoption of different retrieval orientations is associated with distinct neural states. The loci of these sustained effects were distinct from those where new item activity varied, suggesting that the effects may play a role in biasing retrieval cue processing in favor of the current retrieval goal.

Encoding and the durability of episodic memory: a functional magnetic resonance imaging study

Memories vary in their durability even when encoding conditions apparently remain constant. We investigated whether, under these circumstances, memory durability is nonetheless associated with variation in the neural activity elicited during encoding. Event-related functional magnetic resonance imaging data were acquired while volunteers semantically classified visually presented words. Using the "remember/know" procedure, memory for one-half of the words was tested after 30 min and for the remaining half after 48 h. In several regions, including left hippocampus and left dorsal inferior frontal gyrus (IFG), activity at encoding differed depending on whether items were later recollected regardless of study-test delay. Delay-selective effects were also evident, however. Recollection after 48 h was associated with enhanced activity in bilateral ventral IFG, whereas recollection after 30 min was associated with greater fusiform activity. Thus, there is a relationship between the neural activity elicited by an event as it is encoded and the durability of the resulting memory representation.

Effects of Divided Attention on fMRI Correlates of Memory Encoding

Performing a secondary task concurrently with a study task has a detrimental effect on later memory for studied items. To investigate the mechanisms underlying this effect, the processing resources available for an incidental encoding task were varied by manipulating secondary task difficulty. fMRI data were acquired as volunteers (n = 16) made animacy decisions to visually presented study words while concurrently performing either an easy or a hard auditory monitoring task. “Subsequent memory effects”-greater activity at study for words later remembered versus words later forgotten-were identified in the left ventral inferior frontal gyrus and the left anterior hippocampus. These effects did not vary according to whether the encoding task was performed concurrently with the easy or the hard secondary task. However, as secondary task difficulty increased, study-item activity declined and auditory-item activity increased in dorsolateral prefrontal and superior parietal regions that have been implicated in the support of executive and control functions. The findings suggest that dividing attention during encoding influences the probability of engaging the encoding operations that support later episodic memory, but does not alter the nature of the operations themselves. The findings further suggest that the probability of engaging these encoding operations depends on the level of general processing resources engaged in service of the study task.

Content-specificity of the neural correlates of recollection

It is widely assumed that episodic retrieval (recollection) involves reinstatement of cortical activity engaged during the processing of an episode when it was initially experienced. It follows from this assumption that the cortical correlates of recollection should differ with the content of what is recollected, and that retrieval of different content should be associated with activity in functionally distinct cortical regions. The present experiment investigated these predictions. Subjects (N=17) studied a mixed list of words and pictures and were then presented with a test list comprised of words only. Test items were studied words, the names of studied pictures, and unstudied (new) words. Functional magnetic resonance images were acquired while the subjects made Remember/Know/New judgments to these test words. Independent of study material, studied items endorsed as Remembered elicited greater activity than correctly classified unstudied items in several regions, including left frontal, left lateral parietal, and posterior cingulate cortex. In addition, Remembered items elicited greater activity in the right hippocampus and parahippocampal gyrus than items accorded Know judgments, replicating previous findings. Analysis of content-specific effects demonstrated a regional double-dissociation within left fusiform cortex; recollected words elicited greater activity than recollected pictures in lateral fusiform, whereas the reverse effect was evident in an anterior fusiform region. The lateral and anterior fusiform areas correspond closely to areas held to be functionally specialized for the processing of visual words and pictures, respectively. Thus, the current findings support the cortical reinstatement hypothesis of episodic retrieval.

Temporal cortex hypermetabolism in Down syndrome prior to the onset of dementia

BACKGROUND

Adults with Down syndrome (DS) are at increased risk for dementia and provide an opportunity to identify patterns of brain activity that may precede dementia. Studies of early Alzheimer's disease (AD) and risk of AD show decreased function in posterior cingulate and temporal cortex as initial indicators of the disease process, but whether the origin and sequence of predementia brain changes are the same in DS is unknown.

METHODS

The regional cerebral glucose metabolic rates (GMR) among middle-aged nondemented people with DS (n = 17), people with moderate AD (n = 10), and age-matched control subjects (n = 24) were compared using PET during a cognitive task.

RESULTS

Statistical parametric mapping conjunction analyses showed that 1) both DS and AD groups had lower GMR than their respective controls primarily in posterior cingulate and 2) compared with respective controls, the subjects with DS had higher GMR in the same areas of inferior temporal/entorhinal cortex where the AD subjects had lower GMR. The same results were replicated after 1 year of follow-up.

CONCLUSIONS

As the DS subjects were not clinically demented, inferior temporal/entorhinal cortex hypermetabolism may reflect a compensatory response early in disease progression. Compensatory responses may subsequently fail, leading to neurodegenerative processes that the authors anticipate will be detectable in vivo as future GMR decreases in inferior temporal/entorhinal cortex are accompanied by clinical signs of dementia.