Functional dissociation among components of remembering: control, perceived oldness, and content

fMRI evidence of movement familiarization effects on recognition memory in professional dancers

Dual-process theories propose that recognition memory involves recollection and familiarity; however, the impact of motor expertise on memory recognition, especially the interplay between familiarity and recollection, is relatively unexplored. This functional magnetic resonance imaging study used videos of a dancer performing International Latin Dance Styles as stimuli to investigate memory recognition in professional dancers and matched controls. Participants observed and then reported whether they recognized dance actions, recording the level of confidence in their recollections, whereas blood-oxygen-level-dependent signals measured encoding and recognition processes. Professional dancers showed higher accuracy and hit rates for high-confidence judgments, whereas matched controls exhibited the opposite trend for low-confidence judgments. The right putamen and precentral gyrus showed group-based moderation effects, especially for high-confidence (vs. low-confidence) action recognition in professional dancers. During action recognition, the right superior temporal gyrus and insula showed increased activation for accurate recognition and high-confidence retrieval, particularly in matched controls. These findings highlighting enhanced action memory of professional dancers-evident in their heightened recognition confidence-not only supports the dual-processing model but also underscores the crucial role of expertise-driven familiarity in bolstering successful recollection. Additionally, they emphasize the involvement of the action observation network and frontal brain regions in facilitating detailed encoding linked to intention processing.

Widespread frontoparietal fMRI activity is greatly affected by changes in criterion placement, not discriminability, during recognition memory and visual detection tests

Widespread frontoparietal activity is consistently observed in recognition memory tests that compare studied ("target") versus unstudied ("nontarget") responses. However, there are conflicting accounts that ascribe various aspects of frontoparietal activity to mnemonic evidence versus decisional processes. According to Signal Detection Theory, recognition judgments require individuals to decide whether the memory strength of an item exceeds an evidence threshold-the decision criterion-for reporting previously studied items. Yet, most fMRI studies fail to manipulate both memory strength and decision criteria, making it difficult to appropriately identify frontoparietal activity associated with each process. In the current experiment, we manipulated both discriminability and decision criteria across recognition memory and visual detection tests during fMRI scanning to assess how frontoparietal activity is affected by each manipulation. Our findings revealed that maintaining a conservative versus liberal decision criterion drastically affects frontoparietal activity in target versus nontarget response contrasts for both recognition memory and visual detection tests. However, manipulations of discriminability showed virtually no differences in frontoparietal activity in target versus nontarget response or item contrasts. Comparing across task domains, we observed similar modulations of frontoparietal activity across criterion conditions, though the recognition memory task revealed larger activations in both magnitude and spatial extent in these contrasts. Nonetheless, there appears to be some domain specificity in frontoparietal activity associated with the maintenance of a conservative versus liberal criterion. We propose that widespread frontoparietal activity observed in target versus nontarget contrasts is largely attributable to response bias where increased activity may reflect inhibition of a prepotent response, which differs depending on whether a person maintains a conservative versus liberal decision criterion.

Lesion-behavior mapping indicates a strategic role for parietal substrates of associative memory

Numerous neuroimaging studies indicate that ventral parietal cortex (VPC), especially angular gyrus, plays an important role in episodic memory. However, the nature of the mnemonic processes supported by this region is far from clear. We previously found that stroke lesions in VPC and lateral temporal cortex caused deficits in cued recall of unimodal word pairs and picture pairs, and cross-modal picture-sound pairs, with larger deficits in the cross-modal task. However, those findings leave open the question whether those regions' integrity is necessary for maintenance of associative representations, or for strategic processes required for their recall. We addressed this question using associative recognition versions of those tasks. We additionally manipulated semantic relatedness of the associated memoranda, to assess VPC's involvement in semantic processing in the context of episodic memory. We analyzed performance of 62 first-event, sub-acute phase stroke patients (31 right- and 31 left-hemisphere damage) relative to 65 healthy participants, and employed voxel-based lesion-behavior mapping (VLBM) to identify task-relevant structures. Patients displayed greater false associative recognition of semantically related compared to unrelated recombined pairs. VLBM analysis implicated right lateral temporo-parietal regions in associative recognition deficits in the cross-modal pairs task, specifically for related recombined and new pairs, seemingly because of difficulty overcoming semantic relatedness bias effects on episodic discrimination. In contrast, damage to ventral parietal and lateral temporal cortex was not implicated in memory for unrelated memoranda. We interpret this pattern of lesion-behavior effects as indicating lateral temporo-parietal cortex involvement in strategic, rather than representational, roles in episodic associative memory.

Fronto-parietal single-trial brain connectivity benefits successful memory recognition

Successful recognition has been known to produce distinct patterns of neural activity. Many studies have used spectral power or event-related potentials of single recognition-specific regions as classification features. However, this does not accurately reflect the mechanisms behind recognition, in that recognition requires multiple brain regions to work together. Hence, classification accuracy of subsequent memory performance could be improved by using functional connectivity within memory-related brain networks instead of using local brain activity as classifiers. In this study, we examined electroencephalography (EEG) signals while performing a word recognition memory task. Recorded EEG signals were collected using a 32-channel cap. Connectivity measures related to the left hemispheric fronto-parietal connectivity (P3 and F3) were found to contribute to the accurate recognition of previously studied memory items. Classification of subsequent memory outcome using connectivity features revealed that the classifier with support vector machine achieved the highest classification accuracy of 86.79 ± 5.93% (mean ± standard deviation) by using theta (3-8 Hz) connectivity during successful recognition trials. The results strongly suggest that highly accurate classification of subsequent memory outcome can be achieved by using single-trial functional connectivity.

Use of connectotyping on task functional MRI data reveals dynamic network level cross talking during task performance

Task-based functional MRI (fMRI) has greatly improved understanding of brain functioning, enabling the identification of brain areas associated with specific cognitive operations. Traditional analyses are limited to associating activation patterns in particular regions with specific cognitive operation, largely ignoring regional cross-talk or dynamic connectivity, which we propose is crucial for characterization of brain function in the context of task fMRI. We use connectotyping, which efficiently models functional brain connectivity to reveal the progression of temporal brain connectivity patterns in task fMRI. Connectotyping was employed on data from twenty-four participants (12 male, mean age 24.8 years, 2.57 std. dev) who performed a widely spaced event-related fMRI word vs. pseudoword decision task, where stimuli were presented every 20 s. After filtering for movement, we ended up with 15 participants that completed each trial and had enough usable data for our analyses. Connectivity matrices were calculated per participant across time for each stimuli type. A Repeated Measures ANOVA applied on the connectotypes was used to characterize differences across time for words and pseudowords. Our group level analyses found significantly different dynamic connectivity patterns during word vs. pseudoword processing between the Fronto-Parietal and Cingulo-Parietal Systems, areas involved in cognitive task control, memory retrieval, and semantic processing. Our findings support the presence of dynamic changes in functional connectivity during task execution and that such changes can be characterized using connectotyping but not with traditional Pearson’s correlations.

Alpha rhythm modulations in the intraparietal sulcus reflect decision signals during item recognition

Theoretical work and empirical observations suggest a contribution of regions along the intraparietal sulcus to the process of evidence accumulation during episodic memory retrieval. In the present study, we recorded magnetoencephalographic signals in a group of healthy human participants to test whether the pattern of oscillatory modulations in the lateral parietal lobe is consistent with the mnemonic accumulator hypothesis. To this aim, the dynamic properties and the spatial distribution of MEG oscillatory power modulations were investigated during an item recognition task in which the amount of evidence for old vs. new memory decisions was manipulated across three levels. A data-driven approach was employed to identify brain nodes where oscillatory activity was sensitive to both retrieval success and the amount of evidence for old decisions. The analysis identified three nodes in the left lateral parietal lobe where the event-related desynchronization (ERD) in the alpha frequency band showed both effects. Further analyses revealed that the alpha ERD in the intraparietal sulcus, but not in other parietal nodes: i. showed modulation of duration in response to the amount of evidence for both old and new decisions, ii. was behaviorally significant, and iii. more accurately tracked the subjective memory judgment rather than the objective memory status. The present findings provide support for a recent anatomical-functional model of the parietal involvement in episodic memory retrieval and suggest that the alpha ERD in the intraparietal sulcus might represent a neural signature of the evidence accumulation process during simple memory-based decisions.

A Unifying Account of Angular Gyrus Contributions to Episodic and Semantic Cognition

The angular gyrus (AG) region of lateral parietal cortex has been implicated in a wide variety of tasks and functions, generating numerous influential theories. However, these theories largely fail to explain why so many apparently distinct cognitive activities implicate common parietal structures. We propose a unifying model, based on a set of central principles, to account for coalescences of cognitive task activations across AG. To illustrate the proposed framework, we show how these principles account for findings from studies of episodic and semantic memory that have independently implicated the same AG regions but thus far been considered from largely domain-specific perspectives. We conclude that AG computations, as part of a wider lateral parietal system, enable the online dynamic buffering of multisensory spatiotemporally extended representations.

Properties and temporal dynamics of choice- and action-predictive signals during item recognition decisions

Decision-making is in the service of action regardless of whether the decision concerns perceptual information, goods or memories. Compared to recent advances in the neurobiology of perceptual or value-based decisions, however, the neural bases supporting the sampling of evidence in long-term memory, and the transformation of memory-based decisions into appropriate actions, are still poorly understood. In the present fMRI study, we used multivariate pattern analysis to investigate the temporal dynamics of choice- and action-predictive signals during an item recognition task that manipulated the association between memory choices (old/new) and motor responses (eye/hand) across subjects. Choice-predictive activity was mainly observed in striatal, lateral prefrontal and lateral parietal regions, was sensitive to the amount of decision evidence and showed a rapid increase after stimulus onset, followed by a fast decay. Action-predictive signals were found in primary sensory motor, premotor and occipito-parietal regions, were generally observed at the end of the decision phase and were not modulated by decision evidence. These findings suggest that a memory decision variable, potentially represented in a fronto-striato-parietal network, is not directly transformed into an action plan as often observed in perceptual decisions. Regions exhibiting choice predictive activity, and especially the striatum, however, also showed a second peak of decision-related activity that, unlike pure choice- or action-predictive signals, depended on the particular choice-response association. This second peak of activity in the striatum might represent the neural signature of the transformation of a memory decision into an appropriate motor response based on the specific choice-response association.

Activation of stimulus-specific processing regions at retrieval tracks the strength of relational memory

Many theories of episodic memory posit that the subjective experience of recollection may be driven by the activation of stimulus-specific cortical regions during memory retrieval. This study examined cortical activation during associative memory retrieval to identify brain regions that support confidence judgments of source memory in stimulus-specific ways. Adjectives were encoded with either a picture of a face or a scene. During a source memory test, the word was presented alone and the participant was asked if the word had been previously paired with a face or a scene. We identified brain regions that were selectively active when viewing pictures of scenes or faces with a separate localizer scan. We then identified brain regions that were differentially activated to words during the source memory test that had been previously paired with faces or scenes, masked by the localizer activations, and examined how those regions were modulated by the strength of the source memory. Bilateral amygdala activation tracked source memory confidence for faces, while parahippocampal cortex tracked source memory confidence for scenes. The magnitude of the activation of these domain-specific perceptual-processing brain regions during memory retrieval may contribute to the subjective strength of episodic recollection.

Neural evidence for age-related differences in representational quality and strategic retrieval processes

Mounting behavioral evidence suggests that declines in both representational quality and controlled retrieval processes contribute to episodic memory decline with age. The present study sought neural evidence for age-related change in these factors by measuring neural differentiation during encoding of paired associates and changes in regional blood oxygenation level-dependent activity and functional connectivity during retrieval conditions that placed low (intact pairs) and high (recombined pairs) demands on controlled retrieval processes. Pattern similarity analysis revealed age-related declines in the differentiation of stimulus representations at encoding, manifesting as both reduced pattern similarity between closely related events and increased pattern similarity between distinct events. During retrieval, both groups increased recruitment of areas within the core recollection network when endorsing studied pairs, including the hippocampus and angular gyrus. In contrast, only younger adults increased recruitment of, and hippocampal connectivity with, lateral prefrontal regions during correct rejections of recombined pairs. These results provide evidence for age-related changes in representational quality and in the neural mechanisms supporting memory retrieval under conditions of high, but not low, control demand.

Eye fixation-related fronto-parietal neural network correlates of memory retrieval

Eye movements are considered to be informative with regard to the underlying cognitive processes of human beings. Previous studies have reported that eye movements are associated with which scientific concepts are retrieved correctly. Moreover, other studies have also suggested that eye movements involve the cooperative activity of the human brain's fronto-parietal circuits. Less research has been conducted to investigate whether fronto-parietal EEG oscillations are associated with the retrieval processing of scientific concepts. Our findings in this study demonstrated that the fronto-parietal network is indeed crucial for successful memory retrieval. In short, significantly lower theta augmentation in the frontal midline and lower alpha suppression in the right parietal region were observed at the 5th eye fixation for physics concepts that were correctly retrieved than for those that were incorrectly retrieved. Moreover, the visual cortex in the occipital lobe exhibits a significantly greater theta augmentation followed by an alpha suppression following each eye fixation, while a right fronto-parietal asymmetry was also found for the successful retrieval of presentations of physics concepts. In particular, the study results showed that eye fixation-related frontal midline theta power and right parietal alpha power at the 5th eye fixation have the greatest predictive power regarding the correctness of the retrieval of physics concepts.

Motor skill learning induces brain network plasticity: A diffusion-tensor imaging study

Motor skills and the acquisition of brain plasticity are important topics in current research. The development of non-invasive white matter imaging technology, such as diffusion-tensor imaging and the introduction of graph theory make it possible to study the effects of learning skills on the connection patterns of brain networks. However, few studies have characterized the brain network topological features of motor skill learning, especially open skill. Given the need to interact with environmental changes in real time, we hypothesized that the brain network of high-level open-skilled athletes had higher transmission efficiency and stronger interaction in attention, visual and sensorimotor networks. We selected 21 high-level basketball players and 25 ordinary individuals as control subjects, collected their DTI data, built a network of brain structures, and used graph theory to analyze and compare the network properties of the two groups at global and regional levels. In addition, we conducted a correlation analysis on the training years of high-level athletes and brain network nodal parameters on the regional level to assess the relationship between brain network topological characteristics and skills learning. We found that on the global-level, the brain network of high-level basketball players had a shorter path length, small-worldness, and higher global efficiency. On the regional level, the brain nodes of the high-level athletes had nodal parameters that were significantly higher than those of control groups, and were mainly distributed in the visual network, the default mode network, and the attention network. The changes in brain node parameters were significantly related to the number of training years.

Modulating Effects of Contextual Emotions on the Neural Plasticity Induced by Word Learning

Recently, numerous studies have investigated the neurocognitive mechanism of learning words in isolation or in semantic contexts. However, emotion as an important influencing factor on novel word learning has not been fully considered in the previous studies. In addition, the effects of emotion on word learning and the underlying neural mechanism have not been systematically investigated. Sixteen participants were trained to learn novel concrete or abstract words under negative, neutral, and positive contextual emotions over 3 days; then, fMRI scanning was done during the testing sessions on day 1 and day 3. We compared the brain activations in day 1 and day 3 to investigate the role of contextual emotions in learning different types of words and the corresponding neural plasticity changes. Behaviorally, the performance of the words learned in the negative context was lower than those in the neutral and positive contexts, which indicated that contextual emotions had a significant impact on novel word learning. Correspondingly, the functional plasticity changes of the right angular gyrus (AG), bilateral insula, and anterior cingulate cortex (ACC) induced by word learning were modulated by the contextual emotions. The insula also was sensitive to the concreteness of the learned words. More importantly, the functional plasticity changes of the left inferior frontal gyrus (left IFG) and left fusiform gyrus (left FG) were interactively influenced by the contextual emotions and concreteness, suggesting that the contextual emotional information had a discriminable effect on different types of words in the neural mechanism level. These results demonstrate that emotional information in contexts is inevitably involved in word learning. The role of contextual emotions in brain plasticity for learning is discussed.

Failure to Affect Decision Criteria During Recognition Memory With Continuous Theta Burst Stimulation

A decision criterion establishes the minimum amount of memory evidence required for recognition. When a liberal criterion is set, items are recognized based on weak evidence whereas a conservative criterion requires greater memory strength for recognition. The decision criterion is a fundamental aspect of recognition memory but little is known about the underlying neural mechanisms of maintaining a criterion. We used continuous theta burst stimulation (cTBS) with the goal of inhibiting prefrontal cortex excitability while participants performed recognition tests. We hypothesized that inhibiting the right inferior frontal gyrus (rIFG), right middle frontal gyrus (rMFG), and right dorsolateral prefrontal cortex (rDLPFC) would cause participants to establish less conservative decision criteria without affecting recognition memory performance. Participants initially performed recognition memory tests while maintaining conservative decision criteria during fMRI scanning. Peak activity in the successful retrieval effect contrast (Hits > Correct Rejections) provided subject-specific cTBS target sites. During three separate sessions, participants completed the same recognition memory paradigm while maintaining conservative and liberal decision criteria both before and after cTBS. Across two experiments we failed to significantly alter decision criteria placement by applying cTBS to the rIFG, rMFG, and rDLPFC despite efforts to precisely target individualized brain areas. However, we unexpectedly improved discriminability following cTBS to the rDLPFC specifically when participants maintained a liberal criterion. Although this finding may guide future studies investigating the neural mechanisms underlying discriminability in recognition memory, cTBS proved ineffective at altering decision criteria.

A Mini-Review of fMRI Studies of Human Medial Temporal Lobe Activity Associated with Recognition Memory

This review considers event-related functional magnetic resonance imaging (fMRI) studies of human recognition memory that have or have not reported activations within the medial temporal lobes (MTL). For comparisons both between items at study (encoding) and between items at test (recognition), MTL activations are characterized as left/right, anterior/posterior, and hippocampus/surrounding cortex, and as a function of the stimulus material and relevance of item/source information. Though no clear pattern emerges, there are trends suggesting differences between item and source information, and verbal and spatial information, and a role for encoding processes during recognition tests. Important future directions are considered.

Single-Neuron Representation of Memory Strength and Recognition Confidence in Left Human Posterior Parietal Cortex

The human posterior parietal cortex (PPC) is thought to contribute to memory retrieval, but little is known about its specific role. We recorded single PPC neurons of two human tetraplegic subjects implanted with microelectrode arrays, who performed a recognition memory task. We found two groups of neurons that signaled memory-based choices. Memory-selective neurons preferred either novel or familiar stimuli, scaled their response as a function of confidence, and signaled subjective choices regardless of truth. Confidence-selective neurons signaled confidence regardless of stimulus familiarity. Memory-selective signals appeared 553 ms after stimulus onset, but before action onset. Neurons also encoded spoken numbers, but these number-tuned neurons did not carry recognition signals. Together, this functional separation reveals action-independent coding of declarative memory-based familiarity and confidence of choices in human PPC. These data suggest that, in addition to sensory-motor integration, a function of human PPC is to utilize memory signals to make choices.

Rethinking the Role of the Angular Gyrus in Remembering the Past and Imagining the Future: The Contextual Integration Model

Despite consistent activation on tasks of episodic memory, the precise contribution of the left angular gyrus (AG) to mnemonic functions remains vigorously debated. Mounting evidence suggests that AG activity scales with subjective ratings of vividness and confidence in recollection, with further evidence pointing to its involvement during construction of detailed and coherent future simulations. Lesion studies, however, indicate that damage to the AG does not render patients amnesic on standard source and associative memory paradigms. To reconcile these findings, we present the Contextual Integration Model as a unifying framework that couches the mnemonic role of the AG in terms of multimodal integration and representation of contextual information across temporal contexts. Irrespective of whether one is remembering the past or constructing future or hypothetical scenarios, the Contextual Integration Model holds that the core elements of an event (i.e., the who, what, when, where) are bound within the medial temporal lobes while the multimodal details, which give rise to perceptually rich recollection, are integrated and represented in the AG. Building on previous work, the Contextual Integration Model therefore provides a comprehensive exposition of the mnemonic and constructive functions of the AG across temporal contexts, offering a novel test-bed for future work.

Effects of feedback and test practice on recollection and retrieval monitoring: comparing first graders, third graders, and adults

We tested the effects of repeated testing and feedback on recollection accuracy in first graders, third graders, and adults. All participants studied a list of words and pictures, and then took three recollection tests, with each test probing different words and pictures from the earlier study phase. On the first and third tests no feedback was given, whereas on the second test, some subjects received item-level feedback throughout the recollection test. Recollection confusion scores declined across successive tests in all age groups. However, explicit feedback did not improve recollection accuracy or reduce recollection confusions in any age group. We also found that all age groups were able to use picture recollections in a disqualifying monitoring strategy without task experience or feedback. As a whole, these findings suggest that children and adults can use some aspects of retrieval monitoring without feedback or practice, whereas other aspects of retrieval monitoring can benefit from test practice in children and adults. We discuss the potential roles of metacognitive learning and unintended social feedback on these test practice effects.

The contribution of the human posterior parietal cortex to episodic memory

The posterior parietal cortex (PPC) is traditionally associated with attention, perceptual decision making and sensorimotor transformations, but more recent human neuroimaging studies support an additional role in episodic memory retrieval. In this Opinion article, we present a functional-anatomical model of the involvement of the PPC in memory retrieval. Parietal regions involved in perceptual attention and episodic memory are largely segregated and often show a push-pull relationship, potentially mediated by prefrontal regions. Moreover, different PPC regions carry out specific functions during retrieval - for example, representing retrieved information, recoding this information based on task demands, or accumulating evidence for memory decisions.

Reduced multimodal integration of memory features following continuous theta burst stimulation of angular gyrus

BACKGROUND

Lesions of the angular gyrus (AnG) region of human parietal cortex do not cause amnesia, but appear to be associated with reduction in the ability to consciously experience the reliving of previous events.

OBJECTIVES/HYPOTHESIS

We used continuous theta burst stimulation to test the hypothesis that the cognitive mechanism implicated in this memory deficit might be the integration of retrieved sensory event features into a coherent multimodal memory representation.

METHODS

Healthy volunteers received stimulation to AnG or a vertex control site after studying stimuli that each comprised a visual object embedded in a scene, with the name of the object presented auditorily. Participants were then asked to make memory judgments about the studied stimuli that involved recollection of single event features (visual or auditory), or required integration of event features within the same modality, or across modalities.

RESULTS

Participants' ability to retrieve context features from across multiple modalities was significantly reduced after AnG stimulation compared to stimulation of the vertex. This effect was observed only for the integration of cross-modal context features but not for integration of features within the same modality, and could not be accounted for by task difficulty as performance was matched across integration conditions following vertex stimulation.

CONCLUSION

These results support the hypothesis that AnG is necessary for the multimodal integration of distributed cortical episodic features into a unified conscious representation that enables the experience of remembering.

Separating content-specific retrieval from post-retrieval processing

According to cortical reinstatement accounts, neural processes engaged at the time of encoding are re-engaged at the time of memory retrieval. The temporal precision of event-related potentials (ERPs) has been exploited to assess this possibility, and in this study ERPs were acquired while people made memory judgments to visually presented words encoded in two different ways. There were reliable differences between the scalp distributions of the signatures of successful retrieval of different contents from 300 to 1100 ms after stimulus presentation. Moreover, the scalp distributions of these content-sensitive effects changed during this period. These findings are, to our knowledge, the first demonstration in one study that ERPs reflect content-specific processing in two separable ways: first, via reinstatement, and second, via downstream processes that operate on recovered information in the service of memory judgments.

Increased contextual cue utilization with tDCS over the prefrontal cortex during a recognition task

The precise role of the prefrontal and posterior parietal cortices in recognition performance remains controversial, with questions about whether these regions contribute to recognition via the availability of mnemonic evidence or via decision biases and retrieval orientation. Here we used an explicit memory cueing paradigm, whereby external cues probabilistically predict upcoming memoranda as old or new, in our case with 75% validity, and these cues affect recognition decision biases in the direction of the cue. The present study applied bilateral transcranial direct current stimulation (tDCS) over prefrontal or posterior parietal cortex, or sham tDCS, to test the causal role of these regions in recognition accuracy or decision biasing. Participants who received tDCS over prefrontal cortex showed increased cue utilization compared to tDCS over posterior parietal cortex and sham tDCS, suggesting that the prefrontal cortex is involved in processes that contribute to decision biases in memory.

What's the gist? The influence of schemas on the neural correlates underlying true and false memories

The current study used a novel scene paradigm to investigate the role of encoding schemas on memory. Specifically, the study examined the influence of a strong encoding schema on retrieval of both schematic and non-schematic information, as well as false memories for information associated with the schema. Additionally, the separate roles of recollection and familiarity in both veridical and false memory retrieval were examined. The study identified several novel results. First, while many common neural regions mediated both schematic and non-schematic retrieval success, schematic recollection exhibited greater activation in visual cortex and hippocampus, regions commonly shown to mediate detailed retrieval. More effortful cognitive control regions in the prefrontal and parietal cortices, on the other hand, supported non-schematic recollection, while lateral temporal cortices supported familiarity-based retrieval of non-schematic items. Second, both true and false recollection, as well as familiarity, were mediated by activity in left middle temporal gyrus, a region associated with semantic processing and retrieval of schematic gist. Moreover, activity in this region was greater for both false recollection and false familiarity, suggesting a greater reliance on lateral temporal cortices for retrieval of illusory memories, irrespective of memory strength. Consistent with previous false memory studies, visual cortex showed increased activity for true compared to false recollection, suggesting that visual cortices are critical for distinguishing between previously viewed targets and related lures at retrieval. Additionally, the absence of common visual activity between true and false retrieval suggests that, unlike previous studies utilizing visual stimuli, when false memories are predicated on schematic gist and not perceptual overlap, there is little reliance on visual processes during false memory retrieval. Finally, the medial temporal lobe exhibited an interesting dissociation, showing greater activity for true compared to false recollection, as well as for false compared to true familiarity. These results provided an indication as to how different types of items are retrieved when studied within a highly schematic context. Results both replicate and extend previous true and false memory findings, supporting the Fuzzy Trace Theory.

Visual Memory and Visual Perception Recruit Common Neural Substrates

This human neuroimaging review aims to determine the degree to which visual memory evokes activity in neural regions that have been associated with visual perception. A visual perception framework is proposed to identify cortical regions associated with modality-specific processing (i.e., visual, auditory, motor, or olfactory), visual domain-specific processing (i.e., “what” versus “where,” or face versus visual context), and visual feature-specific processing (i.e., color, motion, or spatial location). Independent assessments of visual item memory studies and visual working memory studies revealed activity in the appropriate cortical regions associated with each of the three levels of visual perception processing. These results provide compelling evidence that visual memory and visual perception are associated with common neural substrates. Furthermore, as with visual perception, they support the view that visual memory is a constructive process, in which features or components from disparate cortical regions bind together to form a coherent whole.

Network-Dependent Modulation of COMT and DRD2 Polymorphisms in Healthy Young Adults

Nonlinear modulation of the dopamine signaling on brain functions can be estimated by the interaction effects of dopamine-related genetic variations. We aimed to explore the interaction effects of COMT rs4680 and DRD2 rs1076560 on intra-network connectivity using independent component analysis. In 250 young healthy adults, we identified 11 meaningful resting-state networks (RSNs), including the salience, visual, auditory, default-mode, sensorimotor, attention and frontoparietal networks. A two-way analysis of covariance was used to investigate COMT×DRD2 interactions on intra-network connectivity in each network, controlling for age, gender and education. Significant COMT×DRD2 interaction was found in intra-network connectivity in the left medial prefrontal cortex of the anterior default-mode network, in the right dorsolateral frontal cortex of the right dorsal attention network, and in the left dorsal anterior cingulate cortex of the salience network. Post hoc tests revealed that these interactions were driven by the differential effects of DRD2 genotypes on intra-network connectivity in different COMT genotypic subgroups. Moreover, even in the same COMT subgroup, the modulation effects of DRD2 on intra-network connectivity were different across RSNs. These findings suggest a network-dependent modulation of the DA-related genetic variations on intra-network connectivity.

Laterality effects in functional connectivity of the angular gyrus during rest and episodic retrieval

INTRODUCTION

The angular gyrus (AG) is consistently reported in neuroimaging studies of episodic memory retrieval and is a fundamental node within the default mode network (DMN). Its specific contribution to episodic memory is debated, with some suggesting it is important for the subjective experience of episodic recollection, rather than retrieval of objective episodic details. Across studies of episodic retrieval, the left AG is recruited more reliably than the right. We explored functional connectivity of the right and left AG with the DMN during rest and retrieval to assess whether connectivity could provide insight into the nature of this laterality effect.

METHODS

Using data from the publically available 1000 Functional Connectome Project, 8min of resting fMRI data from 180 healthy young adults were analysed. Whole-brain functional connectivity at rest was measured using a seed-based Partial Least Squares (seed-PLS) approach (McIntosh and Lobaugh, 2004) with bilateral AG seeds. A subsequent analysis used 6-min of rest and 6-min of unconstrained, silent retrieval of autobiographical events from a new sample of 20 younger adults. Analysis of this dataset took a more targeted approach to functional connectivity analysis, consisting of univariate pairwise correlations restricted to nodes of the DMN.

RESULTS

The seed-PLS analysis resulted in two Latent Variables that together explained ~86% of the shared cross-block covariance. The first LV revealed a common network consistent with the DMN and engaging the AG bilaterally, whereas the second LV revealed a less robust, yet significant, laterality effect in connectivity - the left AG was more strongly connected to the DMN. Univariate analyses of the second sample again revealed better connectivity between the left AG and the DMN at rest. However, during retrieval the left AG was more strongly connected than the right to non-medial temporal (MTL) nodes of the DMN, and MTL nodes were more strongly connected to the right AG.

DISCUSSION

The multivariate analysis of resting connectivity revealed that the left and right AG show similar connectivity with the DMN. Only after accounting for this commonality were we able to detect a left laterality effect in DMN connectivity. Further probing with univariate connectivity analyses during retrieval demonstrates that the left preference we observe is restricted to the non-MTL regions of the DMN, whereas the right AG shows significantly better connectivity with the MTL. These data suggest bilateral involvement of the AG during retrieval, despite the focus on the left AG in the literature. Furthermore, the results suggest that the contribution of the left AG to retrieval may be separable from that of the MTL, consistent with a role for the left AG in the subjective aspects of recollection in memory, whereas the MTL and the right AG may contribute to objective recollection of specific memory details.

True and false memories, parietal cortex, and confidence judgments

Recent studies have asked whether activity in the medial temporal lobe (MTL) and the neocortex can distinguish true memory from false memory. A frequent complication has been that the confidence associated with correct memory judgments (true memory) is typically higher than the confidence associated with incorrect memory judgments (false memory). Accordingly, it has often been difficult to know whether a finding is related to memory confidence or memory accuracy. In the current study, participants made recognition memory judgments with confidence ratings in response to previously studied scenes and novel scenes. The left hippocampus and 16 other brain regions distinguished true and false memories when confidence ratings were different for the two conditions. Only three regions (all in the parietal cortex) distinguished true and false memories when confidence ratings were equated. These findings illustrate the utility of taking confidence ratings into account when identifying brain regions associated with true and false memories. Neural correlates of true and false memories are most easily interpreted when confidence ratings are similar for the two kinds of memories.

Effect of emotional valence on retrieval-related recapitulation of encoding activity in the ventral visual stream

While prior work has shown greater retrieval-related reactivation in the ventral visual stream for emotional stimuli compared to neutral stimuli, the effects of valence on retrieval-related recapitulation of successful encoding processes (Dm effects) have yet to be investigated. Here, seventeen participants (aged 19-35) studied line drawings of negative, positive, or neutral images followed immediately by the complete photo. After a 20-min delay, participants performed a challenging recognition memory test, distinguishing the studied line drawing outlines from novel ones. First, results replicated earlier work by demonstrating that negative and positive hits elicited greater ventral occipito-temporal cortex (VOTC) activity than neutral hits during both encoding and retrieval. Moreover, the amount of activation in portions of the VOTC correlated with the magnitude of participants' emotional memory enhancement. Second, results revealed significant retrieval-related recapitulation of Dm effects (Hits>Misses) in VOTC (anterior inferior temporal gyri) only for negative stimuli. Third, connectivity between the amygdala and fusiform gyrus during the encoding of negative stimuli increased the likelihood of fusiform activation during successful retrieval. Together, these results suggest that recapitulation in posterior VOTC reflects memory for the affective dimension of the stimuli (Emotional Hits>Neutral Hits) and the magnitude of activation in some of these regions is related to superior emotional memory. Moreover, for negative stimuli, recapitulation in more anterior portions of the VOTC is greater for remembered than forgotten items. The current study offers new evidence for effects of emotion on recapitulation of activity and functional connectivity in support of memory.

Neural Signatures of Controlled and Automatic Retrieval Processes in Memory-based Decision-making

Decision-making often requires retrieval from memory. Drawing on the neural ACT-R theory [Anderson, J. R., Fincham, J. M., Qin, Y., & Stocco, A. A central circuit of the mind. Trends in Cognitive Sciences, 12, 136-143, 2008] and other neural models of memory, we delineated the neural signatures of two fundamental retrieval aspects during decision-making: automatic and controlled activation of memory representations. To disentangle these processes, we combined a paradigm developed to examine neural correlates of selective and sequential memory retrieval in decision-making with a manipulation of associative fan (i.e., the decision options were associated with one, two, or three attributes). The results show that both the automatic activation of all attributes associated with a decision option and the controlled sequential retrieval of specific attributes can be traced in material-specific brain areas. Moreover, the two facets of memory retrieval were associated with distinct activation patterns within the frontoparietal network: The dorsolateral prefrontal cortex was found to reflect increasing retrieval effort during both automatic and controlled activation of attributes. In contrast, the superior parietal cortex only responded to controlled retrieval, arguably reflecting the sequential updating of attribute information in working memory. This dissociation in activation pattern is consistent with ACT-R and constitutes an important step toward a neural model of the retrieval dynamics involved in memory-based decision-making.

A parietal memory network revealed by multiple MRI methods

The manner by which the human brain learns and recognizes stimuli is a matter of ongoing investigation. Through examination of meta-analyses of task-based functional MRI and resting state functional connectivity MRI, we identified a novel network strongly related to learning and memory. Activity within this network at encoding predicts subsequent item memory, and at retrieval differs for recognized and unrecognized items. The direction of activity flips as a function of recent history: from deactivation for novel stimuli to activation for stimuli that are familiar due to recent exposure. We term this network the 'parietal memory network' (PMN) to reflect its broad involvement in human memory processing. We provide a preliminary framework for understanding the key functional properties of the network.

Parietal lesion effects on cued recall following pair associate learning

We investigated the involvement of the posterior parietal cortex in episodic memory in a lesion-effects study of cued recall following pair-associate learning. Groups of patients who had experienced first-incident stroke, generally in middle cerebral artery territory, and exhibited damage that included lateral posterior parietal regions, were tested within an early post-stroke time window. In three experiments, patients and matched healthy comparison groups executed repeated study and cued recall test blocks of pairs of words (Experiment 1), pairs of object pictures (Experiment 2), or pairs of object pictures and environmental sounds (Experiment 3). Patients' brain CT scans were subjected to quantitative analysis of lesion volumes. Behavioral and lesion data were used to compute correlations between area lesion extent and memory deficits, and to conduct voxel-based lesion-symptom mapping. These analyses implicated lateral ventral parietal cortex, especially the angular gyrus, in cued recall deficits, most pronouncedly in the cross-modal picture-sound pairs task, though significant parietal lesion effects were also found in the unimodal word pairs and picture pairs tasks. In contrast to an earlier study in which comparable parietal lesions did not cause deficits in item recognition, these results indicate that lateral posterior parietal areas make a substantive contribution to demanding forms of recollective retrieval as represented by cued recall, especially for complex associative representations.

Set-relevance Determines the Impact of Distractors on Episodic Memory Retrieval

We investigated the interplay between stimulus-driven attention and memory retrieval with a novel interference paradigm that engaged both systems concurrently on each trial. Participants encoded a 45-min movie on Day 1 and, on Day 2, performed a temporal order judgment task during fMRI. Each retrieval trial comprised three images presented sequentially, and the task required participants to judge the temporal order of the first and the last images (“memory probes”) while ignoring the second image, which was task irrelevant (“attention distractor”). We manipulated the content relatedness and the temporal proximity between the distractor and the memory probes, as well as the temporal distance between two probes. Behaviorally, short temporal distances between the probes led to reduced retrieval performance. Distractors that at encoding were temporally close to the first probe image reduced these costs, specifically when the distractor was content unrelated to the memory probes. The imaging results associated the distractor probe temporal proximity with activation of the right ventral attention network. By contrast, the precuneus was activated for high-content relatedness between distractors and probes and in trials including a short distance between the two memory probes. The engagement of the right ventral attention network by specific types of distractors suggests a link between stimulus-driven attention control and episodic memory retrieval, whereas the activation pattern of the precuneus implicates this region in memory search within knowledge/content-based hierarchies.

Remembering the Past

Our ability to remember past events requires efficient encoding and successful “re-collection” of event features, such as the time, place, people, thoughts, and feelings associated with a past experience. Neuroimaging studies have demonstrated that episodic memory depends on specific brain mechanisms within the prefrontal cortex, medial temporal lobe, and ventral posterior parietal cortex that interact with the cortical sites that store event features. In this article, I present an analysis of the neural correlates of episodic memory, along with a theoretical framework, Cortical Binding of Relational Activity (CoBRA), that integrates the dynamic links between efficient encoding and successful retrieval of episodic memory.

Brain mechanisms of successful recognition through retrieval of semantic context

Episodic memory is associated with the encoding and retrieval of context information and with a subjective sense of reexperiencing past events. The neural correlates of episodic retrieval have been extensively studied using fMRI, leading to the identification of a "general recollection network" including medial temporal, parietal, and prefrontal regions. However, in these studies, it is difficult to disentangle the effects of context retrieval from recollection. In this study, we used fMRI to determine the extent to which the recruitment of regions in the recollection network is contingent on context reinstatement. Participants were scanned during a cued recognition test for target words from encoded sentences. Studied target words were preceded by either a cue word studied in the same sentence (thus congruent with encoding context) or a cue word studied in a different sentence (thus incongruent with encoding context). Converging fMRI results from independently defined ROIs and whole-brain analysis showed regional specificity in the recollection network. Activity in hippocampus and parahippocampal cortex was specifically increased during successful retrieval following congruent context cues, whereas parietal and prefrontal components of the general recollection network were associated with confident retrieval irrespective of contextual congruency. Our findings implicate medial temporal regions in the retrieval of semantic context, contributing to, but dissociable from, recollective experience.

Memory's aging echo: age-related decline in neural reactivation of perceptual details during recollection

Episodic memory decline is a hallmark of normal cognitive aging. Here, we report the first event-related fMRI study to directly investigate age differences in the neural reactivation of qualitatively rich perceptual details during recollection. Younger and older adults studied pictures of complex scenes at different presentation durations along with descriptive verbal labels, and these labels subsequently were used during fMRI scanning to cue picture recollections of varying perceptual detail. As expected from prior behavioral work, the two age groups subjectively rated their recollections as containing similar amounts of perceptual detail, despite objectively measured recollection impairment in older adults. In both age groups, comparisons of retrieval trials that varied in recollected detail revealed robust activity in brain regions previously linked to recollection, including hippocampus and both medial and lateral regions of the prefrontal and posterior parietal cortex. Critically, this analysis also revealed recollection-related activity in visual processing regions that were active in an independent picture-perception task, and these regions showed age-related reductions in activity during recollection that cannot be attributed to age differences in response criteria. These fMRI findings provide new evidence that aging reduces the absolute quantity of perceptual details that are reactivated from memory, and they help to explain why aging reduces the reliability of subjective memory judgments.

The neural basis of involuntary episodic memories

Voluntary episodic memories require an intentional memory search, whereas involuntary episodic memories come to mind spontaneously without conscious effort. Cognitive neuroscience has largely focused on voluntary memory, leaving the neural mechanisms of involuntary memory largely unknown. We hypothesized that, because the main difference between voluntary and involuntary memory is the controlled retrieval processes required by the former, there would be greater frontal activity for voluntary than involuntary memories. Conversely, we predicted that other components of the episodic retrieval network would be similarly engaged in the two types of memory. During encoding, all participants heard sounds, half paired with pictures of complex scenes and half presented alone. During retrieval, paired and unpaired sounds were presented, panned to the left or to the right. Participants in the involuntary group were instructed to indicate the spatial location of the sound, whereas participants in the voluntary group were asked to additionally recall the pictures that had been paired with the sounds. All participants reported the incidence of their memories in a postscan session. Consistent with our predictions, voluntary memories elicited greater activity in dorsal frontal regions than involuntary memories, whereas other components of the retrieval network, including medial-temporal, ventral occipitotemporal, and ventral parietal regions were similarly engaged by both types of memories. These results clarify the distinct role of dorsal frontal and ventral occipitotemporal regions in predicting strategic retrieval and recalled information, respectively, and suggest that, although there are neural differences in retrieval, involuntary memories share neural components with established voluntary memory systems.

Impacts of PICALM and CLU variants associated with Alzheimer's disease on the functional connectivity of the hippocampus in healthy young adults

PICALM rs3851179 and CLU rs11136000 have been recently associated with Alzheimer's disease (AD). Investigating the effects of these genetic variants on the resting-state functional connectivity (rsFC) of the hippocampus may provide new insight into AD pathogenesis. We investigated the main effects and interactions of these two genetic variants on hippocampal rsFC in 283 healthy young adults. The hippocampus showed positive rsFC with the default mode network and negative rsFC with the fronto-parietal network. Risk PICALM G-allele carriers showed weaker negative rsFC compared with AA carriers, whereas risk CLU-CC carriers exhibited stronger positive and negative rsFC than T-allele carriers. There existed complex interactions between PICALM and CLU on the negative rsFC of the hippocampus. Moreover, we found an allele-dependent effect of CLU on hippocampal connectivity when an additive genetic model was applied to CLU. Most of these effects remained significant even after controlling for individual ApoE status. Our results suggest that PICALM and CLU risk genotypes exert differential impacts on the hippocampal rsFC in healthy young subjects. The complex interactions between PICALM and CLU should be considered when investigating the impact of these two genetic variants on the brain.