Rumination and inhibition in task switching: Controlling for episodic retrieval

Rumination is typically defined as the perseverative focus of attention on negative internal thoughts and feelings, which can increase the risk of developing—and severity once developed—of depression. It is thought the perseveration is caused by a deficit in inhibitory control in ruminators. Congruent with this hypothesis, estimates of inhibition in task switching—the n–2 task repetition cost—are negatively associated with estimates of rumination. However, estimates of individual differences of n–2 task repetition costs are hampered by (a) measurement error caused by trial-wise variation in performance, and (b) recent evidence suggesting much of the n–2 task repetition cost measures interference in episodic memory, not inhibition. The aim of the current study is to revisit the question of the association between the n–2 task repetition cost and measures of rumination by (a) statistically accounting for measurement error by estimating n–2 task repetition costs via trial-level Bayesian multilevel modelling, and (b) controlling for episodic interference effects on estimates of n–2 task repetition cost by utilising a paradigm capable of doing so. Together, these methodological and statistical improvements will provide a clearer estimate of the association between inhibition and rumination.

EEG biomarkers of free recall

Brain activity in the moments leading up to successful verbal recall provide a window into the cognitive processes underlying memory retrieval. But these same recordings also subsume neural signals unrelated to mnemonic retrieval, such as response-related motor activity. Here we examined spectral EEG biomarkers of successful recall under an extreme manipulation of mnemonic demands: subjects either recalled items after a few seconds or several days. This manipulation isolated EEG components specifically re- lated to episodic retrieval. Theta and gamma power (4-8 Hz and 40-128 Hz respectively) increased immediately prior to long-delay recall, whereas 8-20 Hz power decreased. A direct comparison of long-delay and immediate recall revealed a nearly identical pattern, indicating that these spectral biomarkers of successful retrieval reflect memory-specific processes. Ruling out a confound of motor related activity, these results identify theta and gamma activity as biomarkers of successful episodic memory retrieval.

Distinct generation of subjective vividness and confidence during naturalistic memory retrieval in the angular gyrus

Subjective experience of remembering is a hallmark of episodic memory, which is deemed crucial for effective behavior. A fundamental and enduring puzzle is the origin of confidence in memory; for example, does the confidence during episodic retrieval depend upon the subjective sensed vividness? The angular gyrus (AnG) exhibits a sensitivity to the subjective experience of remembering, but its direct contribution to the monitoring of subjective mnemonic experience has hitherto been lacking. Here, using a naturalistic video-watching paradigm combined with repetitive transcranial magnetic stimulation (rTMS) and resting-state functional magnetic resonance imaging, we found that pre-retrieval rTMS targeting the left AnG selectively alters the vividness efficiency compared to control stimulation while keeping metacognitive efficiency and objective memory accuracy unaffected. Using trial-wise data, we showed that AnG stimulation altered the mediating role of vividness in confidence in the accuracy of memory judgment. Furthermore, resting-state functional connectivity of hippocampus and AnG was specifically associated with vividness efficiency, while the connectivity of hippocampus and medial prefrontal cortex was associated with metacognitive efficiency across individuals. These findings identify the causal involvement of AnG in gauging the vividness, but not the confidence, of memory, thereby providing evidence for a differentiation account of conscious assessment of memory retrieval.

Distinct generation of subjective vividness and confidence during naturalistic memory retrieval in angular gyrus

Subjective experience of remembering is a hallmark of episodic memory, which enables us to monitor experiences, identify mistakes, and adjust our decisions accordingly. A fundamental and enduring puzzle is the origin of confidence in memory; for example, does the confidence during episodic retrieval depend upon the subjective sensed vividness, or does confidence and vividness reflect dissociable introspective processes? The angular gyrus (AnG) exhibits a sensitivity to subjective experience of remembering, but its direct contribution to the monitoring of internal subjective mnemonic experience has hitherto been lacking. Here we combined a novel naturalistic video-watching paradigm with repetitive transcranial magnetic stimulation (rTMS) and resting-state functional magnetic resonance imaging (fMRI) to test the idea that vividness and confidence are generated differently during retrieval. We found that pre-retrieval rTMS targeting the left AnG selectively alters the vividness efficiency compared to control stimulation while keeping metacognitive efficiency and objective memory accuracy unaffected. Using trial-wise data, we showed that vividness mediates the association between confidence and objective memory accuracy and such mediation was eradicated by AnG stimulation. Furthermore, resting-state functional connectivity of hippocampus and AnG was specifically associated with vividness efficiency, while the connectivity of hippocampus and medial prefrontal cortex was associated with metacognitive efficiency across individuals. These findings identify a role for the AnG in gauging the vividness, but not the confidence, of memory, thereby providing evidence for a differentiation account of conscious assessment of memory by functionally and anatomically dissociating the monitoring of vividness from confidence.

Neural Development of Memory and Metamemory in Childhood and Adolescence: Toward an Integrative Model of the Development of Episodic Recollection

Memory and metamemory processes are essential to retrieve detailed memories and appreciate the phenomenological experience of recollection. Developmental cognitive neuroscience has made strides in revealing the neural changes associated with improvements in memory and metamemory during childhood and adolescence. We argue that hippocampal changes, in concert with surrounding cortical regions, support developmental improvements in the precision, complexity, and flexibility of memory representations. In contrast, changes in frontoparietal regions promote efficient encoding and retrieval strategies. A smaller body of literature on the neural substrates of metamemory development suggests that error monitoring processes implemented in the anterior insula and dorsal anterior cingulate cortex trigger, and perhaps support the development of, metacognitive evaluationsin the prefrontal cortex, while developmental changes in the parietal cortex support changes in the phenomenological experience of episodic retrieval. Our conclusions highlight the necessity of integrating these lines of research into a comprehensive model on the neurocognitive development of episodic recollection.

The convergence and divergence of episodic and semantic functions across lateral parietal cortex

Several decades of neuropsychological and neuroimaging research have highlighted the importance of lateral parietal cortex (LPC) across a myriad of cognitive domains. Yet, despite the prominence of this region the underlying function of LPC remains unclear. Two domains that have placed particular emphasis on LPC involvement are semantic memory and episodic memory retrieval. From each domain, sophisticated models have been proposed as to the underlying function, as well as the more domain-general that LPC is engaged by any form of internally-directed cognition (episodic and semantic retrieval both being examples if this process). Here we directly address these alternatives using a combination of fMRI and DTI white-matter connectivity data. The results show that ventral LPC (angular gyrus) was positively engaged during episodic retrieval but disengaged during semantic memory retrieval. In addition, the level of activity negatively varied with task difficulty in the semantic task whereas episodic activation was independent of difficulty. In contrast, dorsal LPC (intraparietal sulcus) showed domain general activation that was positively correlated with task difficulty. In terms of structural connectivity, a dorsal-ventral and anterior-posterior gradient of connectivity was found to different processing networks (e.g., mid-angular gyrus (AG) connected with episodic retrieval). We propose a unifying model in which LPC as a whole might share a common underlying function (e.g., multimodal buffering) and variations across subregions arise due to differences in the underlying white matter connectivity.

Schematic memories develop quickly, but are not expressed unless necessary

Episodic memory retrieval is increasingly influenced by schematic information as memories mature, but it is unclear whether this is due to the slow formation of schemas over time, or the slow forgetting of the episodes. To address this, we separately probed memory for newly learned schemas as well as their influence on episodic memory decisions. In this experiment, participants encoded images from two categories, with the location of images in each category drawn from a different spatial distribution. They could thus learn schemas of category locations by encoding specific episodes. We found that images that were more consistent with these distributions were more precisely retrieved, and this schematic influence increased over time. However, memory for the schema distribution, measured using generalization to novel images, also became less precise over time. This incongruity suggests that schemas form rapidly, but their influence on episodic retrieval is dictated by the need to bolster fading memory representations.