Anterior medial temporal lobe in human cognition: memory for fear and the unexpected

Neuronal population representation of human emotional memory

Understanding how emotional processing modulates learning and memory is crucial for the treatment of neuropsychiatric disorders characterized by emotional memory dysfunction. We investigate how human medial temporal lobe (MTL) neurons support emotional memory by recording spiking activity from the hippocampus, amygdala, and entorhinal cortex during encoding and recognition sessions of an emotional memory task in patients with pharmaco-resistant epilepsy. Our findings reveal distinct representations for both remembered compared to forgotten and emotional compared to neutral scenes in single units and MTL population spiking activity. Additionally, we demonstrate that a distributed network of human MTL neurons exhibiting mixed selectivity on a single-unit level collectively processes emotion and memory as a network, with a small percentage of neurons responding conjointly to emotion and memory. Analyzing spiking activity enables a detailed understanding of the neurophysiological mechanisms underlying emotional memory and could provide insights into how emotion alters memory during healthy and maladaptive learning.

Cortico-limbic disruption, material-specificity, and deficits in cognitive-affective theory of mind

The Theory of Mind deficit due to cognitive-affective disintegration is a poorly understood cognitive consequence of cortical and subcortical disruption in right temporal lobe epilepsy. Following Marr's trilevel approach, we used the material-specific processing model to understand the Theory of Mind deficit in drug-resistant epilepsy (N = 30). We examined pre- and post-surgery changes in first-order (somatic-affective, non-verbal component) and second-order Theory of Mind (cognitive-verbal component) in three groups formed using: (i) seizure side (right versus left), (ii) right temporal epilepsy (right temporal lobe epilepsy versus non-right temporal lobe epilepsy), and (iii) right temporal lobe epilepsy with amygdalohippocampectomy (right temporal lobe epilepsy versus left temporal lobe epilepsy amygdalohippocampectomy versus non-amygdalohippocampectomy). We observed a marked deficit in the first-order Theory of Mind in the right temporal lobe amygdalohippocampectomy group; we mapped this deficit to decline in the non-verbal component of Theory of Mind (somatic-affective component). Preliminary results support using a material-specific processing model to understand the Theory of Mind deficits in right temporal lobe epilepsy amygdalohippocampectomy. Malleability of verbal processing in presence of deterioration of non-verbal processing might have clinical relevance for post-surgery recovery in right temporal lobe epilepsy amygdalohippocampectomy. Documenting the material-specific nature of deficits (verbal versus non-verbal) in non-western, linguistically, and socioeconomically diverse country enables us to understand the problem of heterogeneity in post-surgery cognitive consequences in the right amygdalohippocampectomy.

Seeing Is Believing: Using Eye-Tracking Devices in Environmental Research

OBJECTIVES

This article aims to provide methodological guidance for research that uses eye-tracking devices (ETDs) to study environment and behavior relationships.

BACKGROUND

Vision is an important human sense through which people acquire a large amount of environmental information. ETDs are tools for detecting eye/gaze behaviors, facilitating better understanding about how people collect visual information and how such information is related to emotions and psychological states. However, there is a lack of guidance for the application of ETDs to environment and behavior studies.

METHODS

A literature review was conducted on articles reporting empirical studies that used ETDs. The data were extracted and compiled, including information such as research questions, research design, types of ETDs, variables measured, types of physical environment (or visual stimuli), stimuli durations, data analysis methods, and so on.

RESULTS

Fifty articles were identified. The main research topics were related to urban and landscape environments, and architecture and interior spaces. Most of the research designs were experimental or quasi-experimental designs, with a few cross-sectional studies. The majority types of ETDs were screen-based ETDs, followed by mobile ETDs (glasses). Main variables were gaze fixations, fixation durations, and scan paths. Typical types of stimuli included images, videos, virtual reality, and real environments and/or objects.

CONCLUSIONS

Guidance for eye-tracking research on environment and behavior was developed based on the literature review results, to provide direction for determining research questions, selecting appropriate research designs, establishing participant inclusion and/or excluding criteria, collecting and analyzing data, and interpreting research results.

Therapist reactions to patient personality: A pilot study of clinicians’ emotional and neural responses using three clinical vignettes from in treatment series

Introduction

Therapists’ responses to patients play a crucial role in psychotherapy and are considered a key component of the patient–clinician relationship, which promotes successful treatment outcomes. To date, no empirical research has ever investigated therapist response patterns to patients with different personality disorders from a neuroscience perspective.

Methods

In the present study, psychodynamic therapists (N = 14) were asked to complete a battery of instruments (including the Therapist Response Questionnaire) after watching three videos showing clinical interactions between a therapist and three patients with narcissistic, histrionic/borderline, and depressive personality disorders, respectively. Subsequently, participants’ high-density electroencephalography (hdEEG) was recorded as they passively viewed pictures of the patients’ faces, which were selected from the still images of the previously shown videos. Supervised machine learning (ML) was used to evaluate whether: (1) therapists’ responses predicted which patient they observed during the EEG task and whether specific clinician reactions were involved in distinguishing between patients with different personality disorders (using pairwise comparisons); and (2) therapists’ event-related potentials (ERPs) predicted which patient they observed during the laboratory experiment and whether distinct ERP components allowed this forecast.

Results

The results indicated that therapists showed distinct patterns of criticized/devalued and sexualized reactions to visual depictions of patients with different personality disorders, at statistically systematic and clinically meaningful levels. Moreover, therapists’ late positive potentials (LPPs) in the hippocampus were able to determine which patient they observed during the EEG task, with high accuracy.

Discussion

These results, albeit preliminary, shed light on the role played by therapists’ memory processes in psychotherapy. Clinical and neuroscience implications of the empirical investigation of therapist responses are discussed.

Regional changes with global brain hypometabolism indicates a physiological triage phenomenon and can explain shared pathophysiological events in Alzheimer's & small vessel diseases and delirium

While reduced global brain metabolism is known in aging, Alzheimer's disease (AD), small vessel disease (SVD) and delirium, explanation of regional brain metabolic (rBM) changes is a challenge. We hypothesized that this may be explained by "triage phenomenon", to preserve metabolic supply to vital brain areas. We studied changes in rBM in 69 patients with at least 5% decline in global brain metabolism during active lymphoma. There was significant decline in the rBM of the inferior parietal, precuneus, superior parietal, lateral occipital, primary visual cortices (P<0.001) and in the right lateral prefrontal cortex (P=0.01). Some areas showed no change; multiple areas had significantly increased rBM (e.g. medial prefrontal, anterior cingulate, pons, cerebellum and mesial temporal cortices; P<0.001). We conclude the existence of a physiological triage phenomenon and argue a new hypothetical model to explain the shared events in the pathophysiology of aging, AD, SVD and delirium.

Altered Metabolic Interrelationships in the Cortico-Limbic Circuitry in Military Service Members with Persistent Post-Traumatic Stress Disorder Symptoms Following Mild Traumatic Brain Injury

Introduction: Comorbid mild traumatic brain injury (mTBI) and post-traumatic stress disorder (PTSD) are common in military service members. The aim of this study is to investigate brain metabolic interrelationships in service members with and without persistent PTSD symptoms after mTBI by using ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography. Methods: Service members (n = 408) diagnosed with mTBI were studied retrospectively. Principal component analysis was applied to identify latent metabolic systems, and the associations between metabolic latent systems and self-report measures of post-concussive and PTSD symptoms were evaluated. Participants were divided into two groups based on DSM-IV-TR (Diagnostic and Statistical Manual of Mental Disorders, fourth edition-Text Revision) criteria for PTSD, and structural equation modeling was performed to test a priori hypotheses on metabolic interrelationships among the brain regions in the cortico-limbic circuitry responsible for top-down control and bottom-up emotional processing. The differences in metabolic interrelationships between age-matched PTSD-absent (n = 204) and PTSD-present (n = 204) groups were evaluated. Results: FDG uptake in the temporo-limbic system was positively correlated with post-concussive and hyperarousal symptoms. For the bottom-up emotional processing, the insula and amygdala-hippocampal complex in the PTSD-present group had stronger metabolic interrelationships with the bilateral rostral anterior cingulate, left lingual, right lateral occipital, and left superior temporal cortices, but a weaker relationship with the right precuneus cortex, compared with the PTSD-absent group. For the top-down control, the PTSD-present group had decreased metabolic engagements of the dorsolateral prefrontal cortex on the amygdala. Discussion: Our results suggest altered metabolic interrelationships in the cortico-limbic circuitry in mTBI subjects with persistent PTSD symptoms, which may underlie the pathophysiological mechanisms of comorbid mTBI and PTSD. Impact statement This is the first ¹⁸F-fluorodeoxyglucose positron emission tomography study to investigate brain metabolic interrelationships in service members with persistent post-traumatic stress disorder (PTSD) symptoms after mild traumatic brain injury (mTBI). We identified that the temporo-limbic metabolic system was associated with post-concussive and hyperarousal symptoms. Further, brain metabolic interrelationships in the cortico-limbic circuitry were altered in mTBI subjects with significant PTSD symptoms compared with those without them.

Anterior Hippocampal-Cortical Functional Connectivity Distinguishes Antipsychotic Naïve First-Episode Psychosis Patients From Controls and May Predict Response to Second-Generation Antipsychotic Treatment

BACKGROUND

Converging evidence implicates the anterior hippocampus in the proximal pathophysiology of schizophrenia. Although resting state functional connectivity (FC) holds promise for characterizing anterior hippocampal circuit abnormalities and their relationship to treatment response, this technique has not yet been used in first-episode psychosis (FEP) patients in a manner that distinguishes the anterior from posterior hippocampus.

METHODS

We used masked-hippocampal-group-independent component analysis with dual regression to contrast subregional hippocampal-whole brain FC between healthy controls (HCs) and antipsychotic naïve FEP patients (N = 61, 36 female). In a subsample of FEP patients (N = 27, 15 female), we repeated this analysis following 8 weeks of second-generation antipsychotic treatment and explored whether baseline FC predicted treatment response using random forest.

RESULTS

Relative to HC, untreated FEP subjects displayed reproducibly lower FC between the left anteromedial hippocampus and cortical regions including the anterior cingulate and insular cortex (P < .05, corrected). Anteromedial hippocampal FC increased in FEP patients following treatment (P < .005), and no longer differed from HC. Random forest analysis showed baseline anteromedial hippocampal FC with four brain regions, namely the insular-opercular cortex, superior frontal gyrus, precentral gyrus, and postcentral gyrus predicted treatment response (area under the curve = 0.95).

CONCLUSIONS

Antipsychotic naïve FEP is associated with lower FC between the anterior hippocampus and cortical regions previously implicated in schizophrenia. Preliminary analysis suggests that random forest models based on hippocampal FC may predict treatment response in FEP patients, and hence could be a useful biomarker for treatment development.

Relating experimentally-induced fear to pre-existing phobic fear in the human brain

While prior work has demonstrated that fear-conditioning changes the neural representation of previously neutral stimuli, it remains unknown to what extent this new representation abstracts away from specific fears and which brain areas are involved therein. To investigate this question, we sought commonalities between experimentally-induced fear via electric shocks and pre-existing phobia. Using functional MRI, we tested the effect of fear-conditioning pictures of dogs in 21 spider-fearful participants across three phases: baseline, post-conditioning, and extinction. Considering phobic stimuli as a reference point for the state of fear allowed us to examine whether fear-conditioning renders information patterns of previously neutral stimuli more similar to those of phobic stimuli. We trained a classification algorithm to discriminate information patterns of neutral stimuli (rats) and phobic stimuli and then tested the algorithm on information patterns from the conditioned stimuli (dogs). Performing this cross-decoding analysis at each experimental phase revealed brain regions in which dogs were classified as rats during baseline, as spiders following conditioning, and again as rats after extinction. A follow-up analysis showed that changes in visual perception information cannot explain the changing classification performance. These results demonstrate a common neural representation for processing fear-eliciting information, either pre-existing or acquired by classical conditioning.

Identifying Sensitive Periods for Alcohol Use: The Roles of Timing and Chronicity of Child Physical Abuse

BACKGROUND

Childhood maltreatment, particularly physical abuse (PA), increases the risk of alcohol use during young adulthood. Although prior research underscores the importance of examining the roles of PA-event characteristics such as timing of and chronicity of PA in initiating and maintaining alcohol use, few studies have explored the risk of developing alcohol use based on the timing and chronicity of PA.

METHODS

Using a community sample of 300 young adults (ages 18 to 25), this study examined how variations in timing and chronicity of PA relate to 4 distinct drinking behaviors including drinking frequency, binge drinking, alcohol-related problems, and alcohol use disorder (AUD) in the past 12 months. We controlled for sociodemographic information, other types of maltreatment, and common risk factors for alcohol use, such as psychological distress, parental alcoholism, and peer alcohol use in all analyses. This study used person-centered and developmental-stage-based characterizations of PA timing and chronicity to explore the relationship between timing and chronicity of PA and later drinking behaviors.

RESULTS

Overall, individuals who were physically abused, particularly during adolescence, and who chronically experienced PA, reported higher levels of monthly drinking frequency and more pathological drinking behaviors such as binge drinking, alcohol-related problems, and AUD.

CONCLUSIONS

This study describes the specific roles of timing and chronicity of PA in understanding the increased vulnerability to alcohol use among victims of PA. Our findings suggest that PA during adolescence and chronic PA are related to problematic drinking behaviors in young adulthood.

A data-driven approach to mapping cortical and subcortical intrinsic functional connectivity along the longitudinal hippocampal axis

The hippocampus (HPC) is functionally heterogeneous along the longitudinal anterior-posterior axis. In rodent models, gene expression maps define at least three discrete longitudinal subregions, which also differ in function, and in anatomical connectivity with the rest of the brain. In humans, equivalent HPC subregions are less well defined, resulting in a lack of consensus in neuroimaging approaches that limits translational study. This study determined whether a data-driven analysis, namely independent component analysis (ICA), could reproducibly define human HPC subregions, and map their respective intrinsic functional connectivity (iFC) with the rest of the brain. Specifically, we performed ICA of resting-state fMRI activity spatially restricted within the HPC, to determine the configuration and reproducibility of functional HPC components. Using dual regression, we then performed multivariate analysis of iFC between resulting HPC components and the whole brain, including detailed connectivity with the hypothalamus, a functionally important connection not yet characterized in human. We found hippocampal ICA resulted in highly reproducible longitudinally discrete components, with greater functional heterogeneity in the anterior HPC, consistent with animal models. Anterior hippocampal components shared iFC with the amygdala, nucleus accumbens, medial prefrontal cortex, posterior cingulate cortex, midline thalamus, and periventricular hypothalamus, whereas posterior hippocampal components shared iFC with the anterior cingulate cortex, retrosplenial cortex, and mammillary bodies. We show that spatially masked hippocampal ICA with dual regression reproducibly identifies functional subregions in the human HPC, and maps their respective brain intrinsic connectivity. Hum Brain Mapp 37:462-476, 2016. © 2015 Wiley Periodicals, Inc.

Large-scale intrinsic functional network organization along the long axis of the human medial temporal lobe

The medial temporal lobe (MTL), encompassing the hippocampus and parahippocampal gyrus (PHG), is a heterogeneous structure which plays a critical role in memory and cognition. Here, we investigate functional architecture of the human MTL along the long axis of the hippocampus and PHG. The hippocampus showed stronger connectivity with striatum, ventral tegmental area and amygdala-regions important for integrating reward and affective signals, whereas the PHG showed stronger connectivity with unimodal and polymodal association cortices. In the hippocampus, the anterior node showed stronger connectivity with the anterior medial temporal lobe and the posterior node showed stronger connectivity with widely distributed cortical and subcortical regions including those involved in sensory and reward processing. In the PHG, differences were characterized by a gradient of increasing anterior-to-posterior connectivity with core nodes of the default mode network. Left and right MTL connectivity patterns were remarkably similar, except for stronger left than right MTL connectivity with regions in the left MTL, the ventral striatum and default mode network. Graph theoretical analysis of MTL-based networks revealed higher node centrality of the posterior, compared to anterior and middle hippocampus. The PHG showed prominent gradients in both node degree and centrality along its anterior-to-posterior axis. Our findings highlight several novel aspects of functional heterogeneity in connectivity along the long axis of the human MTL and provide new insights into how its network organization supports integration and segregation of signals from distributed brain areas. The implications of our findings for a principledunderstanding of distributed pathways that support memory and cognition are discussed.

Human hippocampal processing of environmental novelty during spatial navigation

The detection and processing of novel information encountered as we explore our environment is crucial for learning and adaptive behavior. The human hippocampus has been strongly implicated in laboratory tests of novelty detection and episodic memory, but has been less well studied during more ethological tasks such as spatial navigation, typically used in animals. We examined fMRI BOLD activity as a function of environmental and object novelty as humans performed an object-location virtual navigation task. We found greater BOLD response to novel relative to familiar environments in the hippocampus and adjacent parahippocampal gyrus. Object novelty was associated with increased activity in the posterior parahippocampal/fusiform gyrus and anterior hippocampus extending into the amygdala and superior temporal sulcus. Importantly, whilst mid-posterior hippocampus was more sensitive to environmental novelty than object novelty, the anterior hippocampus responded similarly to both forms of novelty. Amygdala activity showed an increase for novel objects that decreased linearly over the learning phase. By investigating how participants learn and use different forms of information during spatial navigation, we found that medial temporal lobe (MTL) activity reflects both the novelty of the environment and of the objects located within it. This novelty processing is likely supported by distinct, but partially overlapping, sets of regions within the MTL.

Mapping glutamate in subcortical brain structures using high-resolution GluCEST MRI

In vivo measurement of glutamate (Glu) in brain subcortex can elucidate the role these structures play in cognition and neuropsychiatric disorders. However, accurate quantification of Glu in subcortical regions is challenging. Recently, a novel MRI method based on the Glu chemical exchange saturation transfer (GluCEST) effect has been developed for detecting brain Glu in millimolar concentrations. Here, we use GluCEST to map Glu distributions in subcortical structures of the human brain (e.g. amygdala, hippocampus). Overall, GluCEST was ~40% higher in gray matter than in white matter. Within the subcortical gray matters, amygdala showed the highest GluCEST contrast. Utilizing MR spectroscopic data, in vivo GluCEST detection sensitivity (~0.8% mM(-1) ) in subcortical gray matter was evaluated and was consistent with the previously reported values. In general, the GluCEST map approximates the Glu receptor distribution reported in previous positron emission tomography (PET) studies. These findings suggest that high-resolution GluCEST MRI of subcortical brain structures may prove to be a useful tool in diagnosis of brain disorders or treatment responses.

Striatal and hippocampal entropy and recognition signals in category learning: simultaneous processes revealed by model-based fMRI

Category learning is a complex phenomenon that engages multiple cognitive processes, many of which occur simultaneously and unfold dynamically over time. For example, as people encounter objects in the world, they simultaneously engage processes to determine their fit with current knowledge structures, gather new information about the objects, and adjust their representations to support behavior in future encounters. Many techniques that are available to understand the neural basis of category learning assume that the multiple processes that subserve it can be neatly separated between different trials of an experiment. Model-based functional magnetic resonance imaging offers a promising tool to separate multiple, simultaneously occurring processes and bring the analysis of neuroimaging data more in line with category learning's dynamic and multifaceted nature. We use model-based imaging to explore the neural basis of recognition and entropy signals in the medial temporal lobe and striatum that are engaged while participants learn to categorize novel stimuli. Consistent with theories suggesting a role for the anterior hippocampus and ventral striatum in motivated learning in response to uncertainty, we find that activation in both regions correlates with a model-based measure of entropy. Simultaneously, separate subregions of the hippocampus and striatum exhibit activation correlated with a model-based recognition strength measure. Our results suggest that model-based analyses are exceptionally useful for extracting information about cognitive processes from neuroimaging data. Models provide a basis for identifying the multiple neural processes that contribute to behavior, and neuroimaging data can provide a powerful test bed for constraining and testing model predictions.

Serotonin transporter genotype differentially modulates neural responses to emotional words following tryptophan depletion in patients recovered from depression and healthy volunteers

Previous studies have suggested that polymorphism in the serotonin transporter gene (5-HTTLPR) influences responses to serotonergic manipulation, with opposite effects in patients recovered from depression (rMDD) and controls. Here we sought to clarify the neurocognitive mechanisms underpinning these surprising results. Twenty controls and 23 rMDD subjects completed the study; functional magnetic resonance imaging (fMRI) and genotype data were available for 17 rMDD subjects and 16 controls. Following tryptophan or sham depletion, subjects performed an emotional-processing task during fMRI. Although no genotype effects on mood were identified, significant genotype*diagnosis*depletion interactions were observed in the hippocampus and subgenual cingulate in response to emotionally valenced words. In both regions, tryptophan depletion increased responses to negative words, relative to positive words, in high-expression controls, previously identified as being at low-risk for mood change following this procedure. By contrast, in higher-risk low-expression controls and high-expression rMDD subjects, tryptophan depletion had the opposite effect. Increased neural responses to negative words following tryptophan depletion may reflect an adaptive mechanism promoting resilience to mood change following perturbation of the serotonin system, which is reversed in sub-groups vulnerable to developing depressive symptoms. However, this interpretation is complicated by our failure to replicate previous findings of increased negative mood following tryptophan depletion.

Theta and gamma coherence across the septotemporal axis during distinct behavioral states

Theta (4-12 Hz) and gamma (40-100 Hz) field potentials represent the interaction of synchronized synaptic input onto distinct neuronal populations within the hippocampal formation. Theta is quite prominent during exploratory activity, locomotion, and REM sleep. Although it is generally acknowledged that theta is coherent throughout most of the hippocampus, there is significant variability in theta, as well as gamma, coherence across lamina at any particular septotemporal level of the hippocampus. Larger differences in theta coherence are observed across the septotemporal (long) axis. We have reported that during REM sleep there is a decrease in theta coherence across the long axis that varies with the topography of CA3/mossy cell input rather than the topography of the prominent entorhinal input. On the basis of differences in the rat's behavior as well as the activity of neuromodulatory inputs (e.g., noradrenergic and serotonergic), we hypothesized that theta coherence across the long axis would be greater during locomotion than REM sleep and exhibit a pattern more consistent with the topography of entorhinal inputs. We examined theta and gamma coherence indices at different septotemporal and laminar sites during distinct theta states: locomotion during maze running, REM sleep, following acute treatment with a θ-inducing cholinomimetic (physostigmine) and for comparison during slow-wave sleep. The results demonstrate a generally consistent pattern of theta and gamma coherence across the septotemporal axis of the hippocampus that is quite indifferent to sensory input and overt behavior. These results are discussed with regards to the neurobiological mechanisms that generate theta and gamma and the growing body of evidence linking theta and gamma indices to memory and other cognitive functions.

Taking Sides with Pain - Lateralization aspects Related to Cerebral Processing of Dental Pain

The current fMRI study investigated cortical processing of electrically induced painful tooth stimulation of both maxillary canines and central incisors in 21 healthy, right-handed volunteers. A constant current, 150% above tooth specific pain perception thresholds was applied and corresponding online ratings of perceived pain intensity were recorded with a computerized visual analog scale during fMRI measurements. Lateralization of cortical activations was investigated by a region of interest analysis. A wide cortical network distributed over several areas, typically described as the pain or nociceptive matrix, was activated on a conservative significance level. Distinct lateralization patterns of analyzed structures allow functional classification of the dental pain processing system. Namely, certain parts are activated independent of the stimulation site, and hence are interpreted to reflect cognitive emotional aspects. Other parts represent somatotopic processing and therefore reflect discriminative perceptive analysis. Of particular interest is the observed amygdala activity depending on the stimulated tooth that might indicate a role in somatotopic encoding.

Considering PTSD from the perspective of brain processes: a psychological construction approach

Posttraumatic stress disorder (PTSD) is a complex psychiatric disorder that involves symptoms from various domains that appear to be produced by the combination of several mechanisms. The authors contend that existing neural accounts fail to provide a viable model that explains the emergence and maintenance of PTSD and the associated heterogeneity in the expression of this disorder (cf. Garfinkel & Liberzon, 2009). They introduce a psychological construction approach as a novel framework to probe the brain basis of PTSD, where distributed networks within the human brain are thought to correspond to the basic psychological ingredients of the mind. The authors posit that it is the combination of these ingredients that produces the heterogeneous symptom clusters in PTSD. Their goal is show that a constructionist approach has significant heuristic value in understanding the emergence and maintenance of PTSD symptoms, and leads to different and perhaps more useful conjectures about the origins and maintenance of the syndrome than the traditional hyperreactive fear account.

Affective cognition and its disruption in mood disorders

In this review, we consider affective cognition, responses to emotional stimuli occurring in the context of cognitive evaluation. In particular, we discuss emotion categorization, biasing of memory and attention, as well as social/moral emotion. We discuss limited neuropsychological evidence suggesting that affective cognition depends critically on the amygdala, ventromedial frontal cortex, and the connections between them. We then consider neuroimaging studies of affective cognition in healthy volunteers, which have led to the development of more sophisticated neural models of these processes. Disturbances of affective cognition are a core and specific feature of mood disorders, and we discuss the evidence supporting this claim, both from behavioral and neuroimaging perspectives. Serotonin is considered to be a key neurotransmitter involved in depression, and there is a considerable body of research exploring whether serotonin may mediate disturbances of affective cognition. The final section presents an overview of this literature and considers implications for understanding the pathophysiology of mood disorder as well as developing and evaluating new treatment strategies.

Sleep’s Role in the Consolidation of Emotional Episodic Memories

Emotion has a lasting effect on memory, encouraging certain aspects of our experiences to become durable parts of our memory stores. Although emotion exerts its influence at every phase of memory, this review focuses on emotion’s role in the consolidation and transformation of memories over time. Sleep provides ideal conditions for memory consolidation, and recent research demonstrates that manipulating sleep can shed light on the storage and evolution of emotional memories. We provide evidence that sleep enhances the likelihood that select pieces of an experience are stabilized in memory, leading memory for emotional experiences to home in on the aspects of the experience that are most closely tied to the affective response.

Menstrual cycle modulation of medial temporal activity evoked by negative emotion

Previous studies have indicated phase-related differences in HPA activity and amygdala responsiveness in women, such that the response to negative emotional images is reduced during high-estrogen phases of the menstrual cycle. Other research has indicated an opposite effect of exogenous progesterone, increasing amygdala activity at some doses. However, no study to date has assessed the response of the brain's arousal circuitry to negative images during the luteal phase, when both progesterone and estrogen levels are elevated. To address this question, 17 naturally cycling women were each scanned during the early follicular and mid-luteal phases of the cycle, and response to IAPS images was assessed by fMRI. The results indicated significantly increased activity in hippocampus and amygdala during mid-luteal scans when compared to scans in the early follicular phase. These findings suggest that progesterone-mediated effects dominate during the luteal phase, and further suggest that estrogen and progesterone may play opposing roles in modulating the brain's arousal circuitry.

Differential hemodynamic response in affective circuitry with aging: an FMRI study of novelty, valence, and arousal

Emerging evidence indicates that stimulus novelty is affectively potent and reliably engages the amygdala and other portions of the affective workspace in the brain. Using fMRI, we examined whether novel stimuli remain affectively salient across the lifespan, and therefore, whether novelty processing--a potentially survival-relevant function--is preserved with aging. Nineteen young and 22 older healthy adults were scanned during observing novel and familiar affective pictures while estimating their own subjectively experienced aroused levels. We investigated age-related difference of magnitude of activation, hemodynamic time course, and functional connectivity of BOLD responses in the amygdala. Although there were no age-related differences in the peak response of the amygdala to novelty, older individuals showed a narrower, sharper (i.e., "peakier") hemodynamic time course in response to novel stimuli, as well as decreased connectivity between the left amygdala and the affective areas including orbito-frontal regions. These findings have relevance for understanding age-related differences in memory and affect regulation.

Hippocampal pathology in schizophrenia

The hippocampus is abnormal in schizophrenia. Smaller hippocampal volume is the most consistent finding and is present already in the early stages of the illness. The underlying cellular substrate is a subtle, yet functionally significant reduction of hippocampal interneurons. Neuroimaging studies have revealed a pattern of increased hippocampal activity at baseline and decreased recruitment during the performance of memory tasks. Hippocampal lesion models in rodents have replicated some of the pharmacological, anatomical and behavioral phenotype of schizophrenia. Taken together, this pattern of findings points to a disinhibition of hippocampal pyramidal cells and abnormal cortico-hippocampal interactions in schizophrenia.

Amygdala, hippocampal and corpus callosum size following severe early institutional deprivation: the English and Romanian Adoptees study pilot

The adoption into the UK of children who have been reared in severely deprived conditions provides an opportunity to study possible association between very early negative experiences and subsequent brain development. This cross-sectional study was a pilot for a planned larger study quantifying the effects of early deprivation on later brain structure. We used magnetic resonance imaging (MRI) to measure the sizes of three key brain regions hypothesized to be sensitive to early adverse experiences. Our sample was a group of adoptee adolescents (N = 14) who had experienced severe early institutional deprivation in Romania and a group of non-institutionalised controls (N = 11). The total grey and white matter volumes were significantly smaller in the institutionalised group compared with a group of non-deprived, non-adopted UK controls. After correcting for difference in brain volume, the institutionalised group had greater amygdala volumes, especially on the right, but no differences were observed in hippocampal volume or corpus callosum mid-sagittal area. The left amygdala volume was also related to the time spent in institutions, with those experiencing longer periods of deprivation having a smaller left amygdala volume. These pilot findings highlight the need for future studies to confirm the sensitivity of the amygdala to early deprivation.

Intrinsic connections of the macaque monkey hippocampal formation: I. Dentate gyrus

We have carried out a detailed analysis of the intrinsic connectivity of the Macaca fascicularis monkey hippocampal formation. Here we report findings on the topographical organization of the major connections of the dentate gyrus. Localized anterograde tracer injections were made at various rostrocaudal levels of the dentate gyrus, and we investigated the three-dimensional organization of the mossy fibers, the associational projection, and the local projections. The mossy fibers travel throughout the transverse extent of CA3 at the level of the cells of origin. Once the mossy fibers reach the distal portion of CA3, they change course and travel for 3-5 mm rostrally. The associational projection, originating from cells in the polymorphic layer, terminates in the inner one-third of the molecular layer. The associational projection, though modest at the level of origin, travels both rostrally and caudally from the injection site for as much as 80% of the rostrocaudal extent of the dentate gyrus. The caudally directed projection is typically more extensive and denser than the rostrally directed projection. Cells in the polymorphic layer originate local projections that terminate in the outer two-thirds of the molecular layer. These projections are densest at the level of the cells of origin but also extend several millimeters rostrocaudally. Overall, the topographic organization of the intrinsic connections of the monkey dentate gyrus is largely similar to that of the rat. Such extensive longitudinal connections have the potential for integrating information across much of the rostrocaudal extent of the dentate gyrus.