Loss of pattern separation performance in schizophrenia suggests dentate gyrus dysfunction

Motivated by evidence that the dentate gyrus differentially mediates the pattern separation (PS) component of declarative memory function and that dentate gyrus harbors molecular and cellular pathologies in schizophrenia, we examined whether PS performance is altered in volunteers with schizophrenia (SZV) relative to healthy volunteers (HV). In groups of well-characterized SZV (n=14) and HV (n=15), we contrasted performance on the Behavioral Pattern Separation (BPS) Task, acquiring two outcome measures, a PS parameter and a Recognition Memory (RM) parameter, as well as specific recognition data by stimulus type. The SZVs showed a significant decrement in PS performance relative to HV (mean ± SEM, SZV: 3.1 ± 2.7%; HV: 17.1 ± 5.8%; p=0.039, d'=0.86); whereas SZV and HV did not significantly differ in RM performance (SZV: 50.1 ± 8.1%; HV: 59.3 ± 5.5%; p=0.350, d'=0.36). Moreover, the SZVs showed a selective defect in correctly identifying similar lure items (SZV: 24.0 ± 3.7%; HV: 41.2 ± 4.6%; p<0.05), but demonstrated no impairment in identifying targets and novel foils. These data suggest that the dentate gyrus is dysfunctional in schizophrenia, a feature that could contribute to declarative memory impairment in the disorder and possibly to psychosis, a conclusion consistent with the considerable molecular pathology in the dentate gyrus in schizophrenia.

[Interventional radiology procedures for malignancies of the liver: ablation procedures]

Percutaneous ablative procedures allow curative treatment of stage BCLC 0 or BCLC A hepatocellular carcinoma, as well as liver metastases of colorectal cancer. Several methods exist including radiofrequency ablation, the most commonly used. These techniques can be used in combination with surgical excision or alone if surgery is contraindicated. They are associated with significantly reduced mortality as compared to surgery.

[Interventional radiology procedures for malignancies of the liver treatment: Intraarterial procedures]

Intraarterial procedures such as chemoembolization and radioembolization aim for the palliative treatment of advanced hepatocellular carcinoma (stage BCLC B and C with tumoral portal thrombosis). The combination of hepatic intraarterial chemotherapy and systemic chemotherapy can increase the probability of curing colorectal cancer with hepatic metastases not immediately accessible to surgical treatment or percutaneous ablation.

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.

Semantic repetition priming for verbal and pictorial knowledge: a functional MRI study of left inferior prefrontal cortex

Functional neuroimaging studies of single-word processing have demonstrated decreased activation in left inferior prefrontal cortex (LIPC) during repeated semantic processing relative to initial semantic processing. This item-specific memory effect occurs under implicit test instructions and represents word-toword semantic repetition priming. The present study examined the stimulus generality of LIPC function by measuring prefrontal cortical activation during repeated relative to initial semantic processing of words (word-to-word semantic repetition priming) and of pictures (picture-to-picture semantic repetition priming). For both words and pictures, LIPC activation decreased with repetition, suggesting that this area subserves semantic analysis of stimuli regardless of perceptual form. Decreased activation was greater in extent for words than for pictures. The LIPC area may act as a semantic executive system that mediates on-line retrieval of long-term conceptual knowledge necessary for guiding task performance.

Cortical reinstatement mediates the relationship between content-specific encoding activity and subsequent recollection decisions

Episodic recollection entails the conscious remembrance of event details associated with previously encountered stimuli. Recollection depends on both the establishment of cortical representations of event features during stimulus encoding and the cortical reinstatement of these representations at retrieval. Here, we used multivoxel pattern analyses of functional magnetic resonance imaging data to examine how cortical and hippocampal activity at encoding and retrieval drive recollective memory decisions. During encoding, words were associated with face or scene source contexts. At retrieval, subjects were cued to recollect the source associate of each presented word. Neurally derived estimates of encoding strength and pattern reinstatement in occipitotemporal cortex were computed for each encoding and retrieval trial, respectively. Analyses demonstrated that (1) cortical encoding strength predicted subsequent memory accuracy and reaction time, (2) encoding strength predicted encoding-phase hippocampal activity, and (3) encoding strength and retrieval-phase hippocampal activity predicted the magnitude of cortical reinstatement. Path analyses further indicated that cortical reinstatement partially mediated both the effect of cortical encoding strength and the effect of retrieval-phase hippocampal activity on subsequent source memory performance. Taken together, these results indicate that memory-guided decisions are driven in part by a pathway leading from hippocampally linked cortical encoding of event attributes to hippocampally linked cortical reinstatement at retrieval.

Toward open sharing of task-based fMRI data: the OpenfMRI project

The large-scale sharing of task-based functional neuroimaging data has the potential to allow novel insights into the organization of mental function in the brain, but the field of neuroimaging has lagged behind other areas of bioscience in the development of data sharing resources. This paper describes the OpenFMRI project (accessible online at http://www.openfmri.org), which aims to provide the neuroimaging community with a resource to support open sharing of task-based fMRI studies. We describe the motivation behind the project, focusing particularly on how this project addresses some of the well-known challenges to sharing of task-based fMRI data. Results from a preliminary analysis of the current database are presented, which demonstrate the ability to classify between task contrasts with high generalization accuracy across subjects, and the ability to identify individual subjects from their activation maps with moderately high accuracy. Clustering analyses show that the similarity relations between statistical maps have a somewhat orderly relation to the mental functions engaged by the relevant tasks. These results highlight the potential of the project to support large-scale multivariate analyses of the relation between mental processes and brain function.

Human hippocampal increases in low-frequency power during associative prediction violations

Environmental cues often trigger memories of past events (associative retrieval), and these memories are a form of prediction about imminent experience. Learning is driven by the detection of prediction violations, when the past and present diverge. Using intracranial electroencephalography (iEEG), we show that associative prediction violations elicit increased low-frequency power (in the slow-theta range) in human hippocampus, that this low-frequency power increase is modulated by whether conditions allow predictions to be generated, that the increase rapidly onsets after the moment of violation, and that changes in low-frequency power are not present in adjacent perirhinal cortex. These data suggest that associative mismatch is computed within hippocampus when cues trigger predictions that are violated by imminent experience.

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.

Glutamate dysfunction in hippocampus: relevance of dentate gyrus and CA3 signaling

Synaptic glutamate signaling in brain is highly complex and includes multiple interacting receptors, modulating cotransmitters and distinct regional dynamics. Medial temporal lobe (MTL) memory structures receive excitatory inputs from neocortical sensory and associational projections: afferents from neocortex pass to parahippocampal cortex, then to layers II/III of entorhinal cortex, and then onto hippocampal subfields. Principles of Hebbian plasticity govern synaptic encoding of memory signals, and homeostatic plasticity processes influence the activity of the memory system as a whole. Hippocampal imaging studies in schizophrenia have identified 2 alterations in MTL--increases in baseline blood perfusion and decreases in task-related activation. These observations along with converging postsynaptic hippocampal protein changes suggest that homeostatic plasticity mechanisms might be altered in schizophrenia hippocampus. If hippocampal pattern separation is diminished due to partial dentate gyrus failure (resulting in 'spurious associations') and also if pattern completion is accelerated and increasingly inaccurate due to increased CA3 associational activity, then it is conceivable that associations could be false and, especially if driven by anxiety or stress, could generate psychotic content, with the mistaken associations being laid down in memory, despite their psychotic content, especially delusions and thought disorder.

Hippocampal novelty activations in schizophrenia: disease and medication effects

We examined hippocampal activation in schizophrenia (SZ) with fMRI BOLD in response to the presentation of novel and familiar scenes. Voxel-wise analysis showed no group differences. However, anatomical region-of-interest analyses contrasting normal (NL), SZ-on-medication (SZ-ON), SZ-off-medication (SZ-OFF) showed substantial differences in MTL-based novelty responding, accounted for by the reduction in novelty responses in the SZ-OFF predominantly in the anterior hippocampus and parahippocampal cortex. These differences in novelty-based activation in the SZ-OFF group represent disease characteristics of schizophrenia without confounding effects of antipsychotic medication and illustrate the tendency of antipsychotic drug treatment to improve memory functions in schizophrenia.

Content representation in the human medial temporal lobe

Current theories of medial temporal lobe (MTL) function focus on event content as an important organizational principle that differentiates MTL subregions. Perirhinal and parahippocampal cortices may play content-specific roles in memory, whereas hippocampal processing is alternately hypothesized to be content specific or content general. Despite anatomical evidence for content-specific MTL pathways, empirical data for content-based MTL subregional dissociations are mixed. Here, we combined functional magnetic resonance imaging with multiple statistical approaches to characterize MTL subregional responses to different classes of novel event content (faces, scenes, spoken words, sounds, visual words). Univariate analyses revealed that responses to novel faces and scenes were distributed across the anterior-posterior axis of MTL cortex, with face responses distributed more anteriorly than scene responses. Moreover, multivariate pattern analyses of perirhinal and parahippocampal data revealed spatially organized representational codes for multiple content classes, including nonpreferred visual and auditory stimuli. In contrast, anterior hippocampal responses were content general, with less accurate overall pattern classification relative to MTL cortex. Finally, posterior hippocampal activation patterns consistently discriminated scenes more accurately than other forms of content. Collectively, our findings indicate differential contributions of MTL subregions to event representation via a distributed code along the anterior-posterior axis of MTL that depends on the nature of event content.

Esophagogastric cancer: integration of targeted therapies into systemic chemotherapy

Although combination chemotherapy has been shown to be more effective than single agents in advanced esophagogastric cancer, the better response rates have not fulfilled their promise as overall survival times from best combination still range between 8 to 11 months. So far, the development of targeted therapies stays somewhat behind their integration into treatment concepts compared to other gastrointestinal diseases. Thus, the review summarizes the recent advances in the development of targeted therapies in advanced esophagogastric cancer. The majority of agents tested were angiogenesis inhibitors or agents targeting the epidermal growth factor receptors EGFR1 and HER2. For trastuzumab and bevacizumab, phase III trial results have been presented recently. While addition of trastuzumab to cisplatin/5-fluoropyrimidine-based chemotherapy results in a clinically relevant and statistically significant survival benefit in HER 2+ patients, the benefit of the addition of bevacizumab to chemotherapy was not significant. Thus, all patients with metastatic disease should be tested for HER-2 status in the tumor. Trastuzumab in combination with cisplatin/5-fluoropyrimidine-based chemotherapy is the new standard of care for patients with HER2-positive advanced gastric cancer.

Distributed representations in memory: insights from functional brain imaging

Forging new memories for facts and events, holding critical details in mind on a moment-to-moment basis, and retrieving knowledge in the service of current goals all depend on a complex interplay between neural ensembles throughout the brain. Over the past decade, researchers have increasingly utilized powerful analytical tools (e.g., multivoxel pattern analysis) to decode the information represented within distributed functional magnetic resonance imaging activity patterns. In this review, we discuss how these methods can sensitively index neural representations of perceptual and semantic content and how leverage on the engagement of distributed representations provides unique insights into distinct aspects of memory-guided behavior. We emphasize that, in addition to characterizing the contents of memories, analyses of distributed patterns shed light on the processes that influence how information is encoded, maintained, or retrieved, and thus inform memory theory. We conclude by highlighting open questions about memory that can be addressed through distributed pattern analyses.

Multi-voxel patterns of visual category representation during episodic encoding are predictive of subsequent memory

Successful encoding of episodic memories is thought to depend on contributions from prefrontal and temporal lobe structures. Neural processes that contribute to successful encoding have been extensively explored through univariate analyses of neuroimaging data that compare mean activity levels elicited during the encoding of events that are subsequently remembered vs. those subsequently forgotten. Here, we applied pattern classification to fMRI data to assess the degree to which distributed patterns of activity within prefrontal and temporal lobe structures elicited during the encoding of word-image pairs were diagnostic of the visual category (Face or Scene) of the encoded image. We then assessed whether representation of category information was predictive of subsequent memory. Classification analyses indicated that temporal lobe structures contained information robustly diagnostic of visual category. Information in prefrontal cortex was less diagnostic of visual category, but was nonetheless associated with highly reliable classifier-based evidence for category representation. Critically, trials associated with greater classifier-based estimates of category representation in temporal and prefrontal regions were associated with a higher probability of subsequent remembering. Finally, consideration of trial-by-trial variance in classifier-based measures of category representation revealed positive correlations between prefrontal and temporal lobe representations, with the strength of these correlations varying as a function of the category of image being encoded. Together, these results indicate that multi-voxel representations of encoded information can provide unique insights into how visual experiences are transformed into episodic memories.

Associative retrieval processes in the human medial temporal lobe: hippocampal retrieval success and CA1 mismatch detection

Hippocampal subfields CA(3) and CA(1) are hypothesized to differentially support the generation of associative predictions and the detection of associative mismatches, respectively. Using high-resolution functional MRI, we examined hippocampal subfield activation during associative retrieval and during subsequent comparisons of memory to matching or mismatching decision probes. Activity in the dentate gyrus/CA(2/3), CA(1), and other medial temporal lobe subregions tracked associative retrieval success, whereas activity in CA(1) and the perirhinal cortex tracked the presence of associative mismatches. These data support the hypothesis that CA(1) acts as a "comparator," detecting when memory for the past and sensory input in the present diverge.

Reduced hippocampal activity during encoding in cognitively normal adults carrying the APOE ɛ4 allele

Apolipoprotein (APOE) ɛ4-related differences in memory performance have been detected before age 65. The hippocampus and the surrounding medial temporal lobe (MTL) structures are the first site affected by Alzheimer's disease (AD) and the MTL is the seat of episodic memory, including visuo-spatial memory. While reports of APOE ɛ4-related differences in these brain structures are not consistent in either cross-sectional or longitudinal structural and functional magnetic resonance imaging (fMRI) studies, there is increasing evidence that brain activity at baseline (defined as activity during fixation or rest) may differ in APOE ɛ4 carriers compared to non-carriers. In this fMRI study, cognitively normal APOE ɛ4 carriers and non-carriers engaged in a perspective-dependent spatial learning task (Shelton & Gabrieli, 2002) previously shown to activate MTL structures in older participants (Borghesani et al., 2008). A low-level, visually engaging dot-control task was used for comparison, in addition to fixation. APOE ɛ4 carriers showed less activation than non-carriers in the hippocampus proper during encoding. Specifically, when spatial encoding was contrasted against the dot-control task, encoding-related activation was significantly lower in carriers than non-carriers. By contrast, no ɛ4-related differences in the hippocampus were found when spatial encoding was compared with fixation. Lower activation, however, was not global since encoding-related activation in early visual cortex (left lingual gyrus) was not different between APOE ɛ4 carriers and non-carriers. The present data document APOE ɛ4-related differences in the hippocampus proper during encoding and underscore the role of low-level control contrasts for complex encoding tasks. These results have implications for fMRI studies that investigate the default-mode network (DMN) in middle-aged to older APOE ɛ4 carriers to help evaluate AD risk in this otherwise cognitively normal population.

Cognitive control and right ventrolateral prefrontal cortex: reflexive reorienting, motor inhibition, and action updating

Delineating the functional organization of the prefrontal cortex is central to advancing models of goal-directed cognition. Considerable evidence indicates that specific forms of cognitive control are associated with distinct subregions of the left ventrolateral prefrontal cortex (VLPFC), but less is known about functional specialization within the right VLPFC. We report a functional MRI meta-analysis of two prominent theories of right VLPFC function: stopping of motor responses and reflexive orienting to abrupt perceptual onsets. Along with a broader review of right VLPFC function, extant data indicate that stopping and reflexive orienting similarly recruit the inferior frontal junction (IFJ), suggesting that IFJ supports the detection of behaviorally relevant stimuli. By contrast, other right VLPFC subregions are consistently active during motor inhibition, but not reflexive reorienting tasks, with posterior-VLPFC being active during the updating of action plans and mid-VLPFC responding to decision uncertainty. These results highlight the rich functional heterogeneity that exists within right VLPFC.

Cognitive control and right ventrolateral prefrontal cortex: reflexive reorienting, motor inhibition, and action updating

Delineating the functional organization of the prefrontal cortex is central to advancing models of goal-directed cognition. Considerable evidence indicates that specific forms of cognitive control are associated with distinct subregions of the left ventrolateral prefrontal cortex (VLPFC), but less is known about functional specialization within the right VLPFC. We report a functional MRI meta-analysis of two prominent theories of right VLPFC function: stopping of motor responses and reflexive orienting to abrupt perceptual onsets. Along with a broader review of right VLPFC function, extant data indicate that stopping and reflexive orienting similarly recruit the inferior frontal junction (IFJ), suggesting that IFJ supports the detection of behaviorally relevant stimuli. By contrast, other right VLPFC subregions are consistently active during motor inhibition, but not reflexive reorienting tasks, with posterior-VLPFC being active during the updating of action plans and mid-VLPFC responding to decision uncertainty. These results highlight the rich functional heterogeneity that exists within right VLPFC.

Expected value information improves financial risk taking across the adult life span

When making decisions, individuals must often compensate for cognitive limitations, particularly in the face of advanced age. Recent findings suggest that age-related variability in striatal activity may increase financial risk-taking mistakes in older adults. In two studies, we sought to further characterize neural contributions to optimal financial risk taking and to determine whether decision aids could improve financial risk taking. In Study 1, neuroimaging analyses revealed that individuals whose mesolimbic activation correlated with the expected value estimates of a rational actor made more optimal financial decisions. In Study 2, presentation of expected value information improved decision making in both younger and older adults, but the addition of a distracting secondary task had little impact on decision quality. Remarkably, provision of expected value information improved the performance of older adults to match that of younger adults at baseline. These findings are consistent with the notion that mesolimbic circuits play a critical role in optimal choice, and imply that providing simplified information about expected value may improve financial risk taking across the adult life span.

The hippocampal formation in schizophrenia

The hippocampal formation is one of the most extensively studied regions of the brain, with well-described anatomy and basic physiology; moreover, aspects of human memory mediated by the hippocampus are well characterized. In schizophrenia, alterations in hippocampal anatomy, perfusion, and activation are consistently reported; impairments in declarative memory function, especially in the flexible use of event memories (e.g., in the service of memory-based inference), are common. Postmortem molecular changes suggest a selective reduction in glutamate transmission in the dentate gyrus and in its efferent fibers, the mossy fiber pathway. A reduction in dentate gyrus glutamatergic output and in its information processing functions could generate two co-occurring outcomes in the hippocampus: 1) a change in homeostatic plasticity processes in cornu ammonis 3 (CA3), accompanied by increased activity due to reduced afferent stimulation from the dentate gyrus onto CA3 neurons, a process that could increase the pattern completion functions of CA3, and 2) the loss of mnemonic functions specific to the dentate gyrus, namely pattern separation, a change that could increase the prevalence of illusory pattern completion and reduce discrimination between present and past experiences in memory. The resulting increase in "runaway" CA3-mediated pattern completion could result in cognitive "mistakes," generating psychotic associations and resulting in memories with psychotic content. Tests of this model could result in novel approaches to the treatment of psychosis and declarative memory alterations and in novel animal preparations for basic schizophrenia research.

High-resolution fMRI of content-sensitive subsequent memory responses in human medial temporal lobe

The essential role of the medial temporal lobe (MTL) in long-term memory for individual events is well established, yet important questions remain regarding the mnemonic functions of the component structures that constitute the region. Within the hippocampus, recent functional neuroimaging findings suggest that formation of new memories depends on the dentate gyrus and the CA(3) field, whereas the contribution of the subiculum may be limited to retrieval. During encoding, it has been further hypothesized that structures within MTL cortex contribute to encoding in a content-sensitive manner, whereas hippocampal structures may contribute to encoding in a more domain-general manner. In the current experiment, high-resolution fMRI techniques were utilized to assess novelty and subsequent memory effects in MTL subregions for two classes of stimuli--faces and scenes. During scanning, participants performed an incidental encoding (target detection) task with novel and repeated faces and scenes. Subsequent recognition memory was indexed for the novel stimuli encountered during scanning. Analyses revealed voxels sensitive to both novel faces and novel scenes in all MTL regions. However, similar percentages of voxels were sensitive to novel faces and scenes in perirhinal cortex, entorhinal cortex, and a combined region comprising the dentate gyrus, CA(2), and CA(3), whereas parahippocampal cortex, CA(1), and subiculum demonstrated greater sensitivity to novel scene stimuli. Paralleling these findings, subsequent memory effects in perirhinal cortex were observed for both faces and scenes, with the magnitude of encoding activation being related to later memory strength, as indexed by a graded response tracking recognition confidence, whereas subsequent memory effects were scene-selective in parahippocampal cortex. Within the hippocampus, encoding activation in the subiculum correlated with subsequent memory for both stimulus classes, with the magnitude of encoding activation varying in a graded manner with later memory strength. Collectively, these findings suggest a gradient of content sensitivity from posterior (parahippocampal) to anterior (perirhinal) MTL cortex, with MTL cortical regions differentially contributing to successful encoding based on event content. In contrast to recent suggestions, the present data further indicate that the subiculum may contribute to successful encoding irrespective of event content.