Encoding of emotional memories depends on amygdala and hippocampus and their interactions

Amygdala volume loss in patients with dysphoric disorder of epilepsy

A categorical approach to the study of amygdala volumes in specific neuropsychiatric disorders leads to contradictory findings. In an alternative dimensional approach, we tested the hypothesis that amygdala volume loss represents specific dimensions of affective syndromes in patients with epilepsy. One hundred sixty patients with chronic therapy-refractory epilepsy were carefully diagnosed for psychiatric symptoms. Fifty-three patients without any lifetime psychopathology (n=24), with dysphoric disorder of epilepsy (n=12), or with major depressive disorder (n=17) were included. Amygdala and hippocampal volumes were measured using established protocols. Amygdala volumes were significantly reduced in patients with dysphoric disorder of epilepsy and correlated significantly with core symptoms of dysphoric disorder of epilepsy, that is, emotional instability, dysphoria, irritability, and aggression. Our finding supports a dimensional concept of the meaning of brain alterations and validates the clinical concept of dysphoric disorder of epilepsy.

Genetic variation in the G72 (DAOA) gene affects temporal lobe and amygdala structure in subjects affected by bipolar disorder

BACKGROUND

Variation in the G72 (DAOA) gene is understood to convey susceptibility for bipolar disorder through an uncertain mechanism. Little is known about the structural brain phenotypes associated with this gene. We hypothesised that reductions in temporal lobe and amygdala gray matter would be associated with variation at two loci in the gene for which evidence of genetic linkage has been repeatedly demonstrated.

METHODS

We examined the temporal lobe and amygdala gray matter associations of the risk variants M23 and M24 at the 5' end of the gene encoding G72 in 81 controls and 38 people with bipolar disorder.

RESULTS

Genetic variation at both the M23 and M24 loci in G72 were associated with decreased gray matter density within the left temporal pole in people with bipolar disorder. M23 was also associated with reductions in right amygdala gray matter density. The genetic imaging associations were found only in patients with bipolar disorder.

CONCLUSIONS

Genetic variation at single nucleotide polymorphisms in the G72 gene previously associated with bipolar disorder is related to reductions in temporal pole and amygdala gray matter structure in people with bipolar disorder.

Enhanced activity during associative encoding in the affected hippocampus in right temporal lobe epilepsy patients

Mnestic deficits represent the core cognitive impairment of patients with temporal lobe epilepsy (TLE), irrespective of the existence of overt morphological lesions. Compared to controls, patients with symptomatic TLE show altered functional activation patterns in fMRI studies on memory processes. But, so far, such studies have rarely investigated patients with temporal lobe epilepsy of unknown cause. Therefore, in the current study, a small sample of 6 right TLE patients with normal structural MRIs was compared to controls with respect to brain activity during encoding of face-name associations using fMRI. Compared to controls, patients retrieved fewer face-name associations correctly, but showed significantly greater activation of the affected hippocampus for successfully encoded stimuli. Therefore, higher hippocampal activation seems necessary for successful encoding of associations in patients compared to controls. But, this process is not entirely successful since the patients cannot achieve the same performance as controls. In conclusion, the hyperactivation of the hippocampus might represent a compensational but inefficient process.

Cholinergic stimulation enhances neural activity associated with encoding but reduces neural activity associated with retrieval in humans

The cerebral cholinergic system is centrally involved in memory formation. Studies in rodents suggest that cholinergic stimulation may facilitate encoding of new information but may interfere with retrieval. We investigated the effect of cholinergic stimulation on encoding and retrieval of episodic memory in humans. We also tested whether the putative benefit of cholinergic stimulation on memory function depends on individual baseline performance. Since such effects were expected to be greatest in an older population resulting from an age-related degeneration of the cholinergic system, we recruited 22 healthy older subjects (51-68 years) for an event-related functional magnetic resonance imaging experiment. In two separate scanning sessions, subjects encoded and retrieved items and their spatial context under cholinergic stimulation or placebo with the acetylcholine-esterase inhibitor physostigmine or saline being administered intravenously in a double-blind cross-over design. Baseline performance was recorded at a separate occasion without scanning. Cholinergic stimulation enhanced neural activity for successful versus unsuccessful spatial context encoding in the right hippocampus but reduced activity for successful versus unsuccessful spatial context retrieval in the right amygdala. These data may bridge the gap between rodent and human studies by showing that also in man cholinergic stimulation enhances encoding but interferes with retrieval on a neural level. Furthermore, baseline performance negatively correlated with the effect of cholinergic stimulation. Thus, participants who were worse at baseline benefited more from cholinergic stimulation than those who had better baseline values, indicating that a cholinergic deficit contributes to the memory decline even in healthy older subjects.

Emotional content does not interfere with verbal memory in patients with temporal lobe epilepsy

In healthy humans, memory for words with emotional valence is better than memory for neutral words. At the same time, the word preceding the emotional word in a word list learning task is remembered less often than other neutral words. Both effects, enhanced memory for emotional words and retrograde amnesia for preceding words, are dependent on intactness of the amygdala. In this study we asked whether patients with temporal lobe epilepsy (TLE), a disease that often involves the amygdala as well, show altered memory for emotional words and the words presented in close temporal proximity. Whereas we found enhanced memory performance for emotional and decreased recognition performance for the preceding and successive word in our 19 control subjects, both effects were strongly reduced in our 21 patients. No group differences occurred in memory for perceptually deviant words. The lack of emotion effects on memory in the patients cannot simply be attributed to altered perception of emotions as the patients rated the emotionality of the words no different than control subjects. Hence, we conclude that patients with TLE have a specific deficit in the emotion-driven encoding enhancement mediated by the amygdala-hippocampus loop.

Dopamine release during human emotional processing

Involvement of dopamine neurotransmission in human emotional processing is unclear but animal studies have indicated that it is critical for processing of fear response. In this experiment we examined dopaminergic involvement in the processing of human emotions. We used a novel dynamic molecular imaging technique to detect and map dopamine released during presentation of emotional stimuli. The technique exploited the competition between endogenously released dopamine and its ligand for receptor occupancy and involved dynamic voxel-wise measurement of the rate at which a dopamine receptor ligand ((18)F-Fallypride) was displaced from receptor sites during emotional processing. An increase in the rate indicated dopamine release. We found that the rate of ligand displacement increased significantly in the left amygdala, left medial temporal lobe (MTL) and left inferior frontal gyrus. The results provide the first direct evidence of dopaminergic modulation of human emotional processing and suggest that the modulation occurs at multiple levels of processing. This finding indicates that the neurocognitive models of human emotion should take into account dopaminergic effects, and that, there is a need to investigate whether manipulation of the dopaminergic system could be an alternate strategy for treatment of conditions in which emotional processing is impaired.

The Berlin Affective Word List Reloaded (BAWL-R)

The study presented here provides researchers with a revised list of affective German words, the Berlin Affective Word List Reloaded (BAWL-R). This work is an extension of the previously published BAWL (Võ, Jacobs, & Conrad, 2006), which has enabled researchers to investigate affective word processing with highly controlled stimulus material. The lack of arousal ratings, however, necessitated a revised version of the BAWL. We therefore present the BAWL-R, which is the first list that not only contains a large set of psycholinguistic indexes known to influence word processing, but also features ratings regarding emotional arousal, in addition to emotional valence and imageability. The BAWL-R is intended to help researchers create stimulus material for a wide range of experiments dealing with the affective processing of German verbal material.

Age-related differences in brain regions supporting successful encoding of emotional faces

In an event-related functional Magnetic Resonance Imaging (fMRI) study, younger and older adults were presented with negative emotional (i.e., fearful) and neutral face pictures under incidental learning conditions. They were subsequently given a test of face recognition outside the scanner. Both age groups activated amygdala bilaterally as well as the right hippocampus during successful encoding of the fearful faces. Direct age comparisons revealed greater activation in right amygdala and bilateral hippocampus in the young, whereas older adults showed greater activation in the left insular and right prefrontal cortices. None of these brain areas was activated during successful encoding of neutral faces, suggesting specificity of these brain activation patterns. The results indicate an age-related shift in the neural underpinnings of negative emotional face processing from medial-temporal to neocortical regions.

From high anxiety trait to depression: a neurocognitive hypothesis

Although exposure to substantial stress has a major impact on the development of depression, there is considerable variability in the susceptibility of individuals to the adverse effects of stress. The personality trait of high anxiety has been identified as a vulnerability factor to develop depression. We propose here a new unifying model based on a series of neurocognitive mechanisms (and fed with crucial information provided by research on the fields of emotion, stress and cognition) whereby individuals presenting a high anxiety trait are particularly vulnerable to develop depression when facing stress and adversity. Our model highlights the importance of developing prevention programs addressed to restrain, in high anxious individuals, the triggering of a dysfunctional neurocognitive cascade while coping with stress.

Pharmacotherapy of PTSD: premises, principles, and priorities

Post-traumatic stress disorder (PTSD) is a prevalent anxiety disorder that results in multiple disabling symptoms. Research into the underlying neurobiology has implicated dysregulation in multiple neurotransmitter systems including norepinephrine, serotonin, and glutamate as well as the hypothalamic-pituitary axis. Understanding how these biological systems interact with each other and how they may affect key neural structures, such as the amygdala, hippocampus, and prefrontal cortex, to produce post-traumatic symptoms is critical for the development of effective pharmacological treatments. We briefly discuss the proposed biological dysfunctions underlying PTSD and how agents that target these dysfunctions may be utilized in PTSD. We then provide a review of the different pharmacological agents that have been investigated in PTSD. These drugs include: antidepressants, anti-adrenergic agents, anticonvulsants, benzodiazepines, atypical antipsychotics, and novel agents.

Declarative memory is critical for sustained advantageous complex decision-making

Previous studies have reported conflicting evidence concerning the contribution of declarative memory to advantageous decision-making on the Iowa Gambling Task (IGT). One study, in which the measurement of psychophysiology during the task necessitated a 10-s delay between card selections, found that six participants with amnesia due to hippocampal damage failed to develop a preference for advantageous decks over disadvantageous decks [Gutbrod, K., Krouzel, C., Hofer, H., Muri, R., Perrig, W., & Ptak, R. (2006). Decision-making in amnesia: Do advantageous decisions require conscious knowledge of previous behavioural choices? Neuropsychologia, 44(8), 1315-1324]. However, a single-case study (where psychophysiology was not measured and no delay between card selections occurred) showed that an amnesic patient developed normal preference for advantageous decks [Turnbull, O. H., & Evans, C. E. (2006). Preserved complex emotion-based learning in amnesia. Neuropsychologia, 44(2), 300-306]. We sought to resolve these discrepant findings by examining IGT performances in five patients with profound amnesia (WMS-III General Memory Index M=63) and bilateral hippocampal damage caused by anoxia (n=4) or herpes simplex encephalitis (n=1). In one administration of the IGT, psychophysiology measurements were utilized and a 6-s delay was interposed between card selections. In a second administration, no delay between card selections was interposed. While age-, sex-, and education-matched healthy comparison participants showed significant learning with a gradual preference for advantageous decks in both conditions, amnesic patients, irrespective of IGT administration condition and extent of medial temporal lobe damage, failed to develop this preference. These findings strongly discount the possibility that the delay between card selections explains why amnesic participants fail to learn in the IGT, and suggest instead a significant role for medial temporal lobe declarative memory systems in the type of complex decision-making tapped by the IGT.

Towards a theory of chronic pain

In this review, we integrate recent human and animal studies from the viewpoint of chronic pain. First, we briefly review the impact of chronic pain on society and address current pitfalls of its definition and clinical management. Second, we examine pain mechanisms via nociceptive information transmission cephalad and its impact and interaction with the cortex. Third, we present recent discoveries on the active role of the cortex in chronic pain, with findings indicating that the human cortex continuously reorganizes as it lives in chronic pain. We also introduce data emphasizing that distinct chronic pain conditions impact on the cortex in unique patterns. Fourth, animal studies regarding nociceptive transmission, recent evidence for supraspinal reorganization during pain, the necessity of descending modulation for maintenance of neuropathic behavior, and the impact of cortical manipulations on neuropathic pain is also reviewed. We further expound on the notion that chronic pain can be reformulated within the context of learning and memory, and demonstrate the relevance of the idea in the design of novel pharmacotherapies. Lastly, we integrate the human and animal data into a unified working model outlining the mechanism by which acute pain transitions into a chronic state. It incorporates knowledge of underlying brain structures and their reorganization, and also includes specific variations as a function of pain persistence and injury type, thereby providing mechanistic descriptions of several unique chronic pain conditions within a single model.

Neural correlates of associative memory: the effects of negative emotion

We explored brain activation associated with negative emotionality, during an associative memory task that involved the encoding and retrieval of word pairs. Participants were instructed to memorize word pairs and subsequently retrieve them. The word pairs consisted of either emotional or neutral words. Significant hippocampal activation was observed during both encoding and retrieval of the neutral word pairs, and was correlated with correct response rates during retrieval. However, the negative word pairs activated the left middle temporal gyrus during both encoding and retrieval. These results suggest that hippocampal activation is involved in both the encoding and retrieval of word pairs. However, negative emotionality does not necessarily enhance hippocampal activity and memory performance.

Remembering the Details: Effects of Emotion

Though emotion conveys memory benefits, it does not enhance memory equally for all aspects of an experience nor for all types of emotional events. In this review, I outline the behavioral evidence for arousal's focal enhancements of memory and describe the neural processes that may support those focal enhancements. I also present behavioral evidence to suggest that these focal enhancements occur more often for negative experiences than for positive ones. This effect of valence appears to arise because of valence-dependent effects on the neural processes recruited during episodic encoding and retrieval, with negative affect associated with increased engagement of sensory processes and positive affect leading to enhanced recruitment of conceptual processes.

A developmental examination of amygdala response to facial expressions

Several lines of evidence implicate the amygdala in face-emotion processing, particularly for fearful facial expressions. Related findings suggest that face-emotion processing engages the amygdala within an interconnected circuitry that can be studied using a functional-connectivity approach. Past work also underscores important functional changes in the amygdala during development. Taken together, prior research on amygdala function and development reveals a need for more work examining developmental changes in the amygdala's response to fearful faces and in amygdala functional connectivity during face processing. The present study used event-related functional magnetic resonance imaging to compare 31 adolescents (9-17 years old) and 30 adults (21-40 years old) on activation to fearful faces in the amygdala and other regions implicated in face processing. Moreover, these data were used to compare patterns of amygdala functional connectivity in adolescents and adults. During passive viewing, adolescents demonstrated greater amygdala and fusiform activation to fearful faces than did adults. Functional connectivity analysis revealed stronger connectivity between the amygdala and the hippocampus in adults than in adolescents. Within each group, variability in age did not correlate with amygdala response, and sex-related developmental differences in amygdala response were not found. Eye movement data collected outside of the magnetic resonance imaging scanner using the same task suggested that developmental differences in amygdala activation were not attributable to differences in eye-gaze patterns. Amygdala hyperactivation in response to fearful faces may explain increased vulnerability to affective disorders in adolescence; stronger amygdala-hippocampus connectivity in adults than adolescents may reflect maturation in learning or habituation to facial expressions.

Emotional memory in schizophrenia

Emotional memories play an important role in our day-to-day experience, informing many of our minute-to-minute decisions (eg, where to go for dinner, what are the likely consequences of not attending a meeting), as well as our long-term goal setting. Individuals with schizophrenia appear to be impaired in memory for emotional experiences, particularly over longer delay periods, which may contribute to deficits in goal-related behavior and symptoms of amotivation and anhedonia. This article reviews factors that are known to influence emotional memory in healthy subjects, applies these factors to results from emotional memory studies with individuals with schizophrenia, and then uses extant neurobiological models of emotional memory formation to develop hypotheses about biological processes that might particularly contribute to emotional memory impairment in schizophrenia.

Prefrontal social cognition network dysfunction underlying face encoding and social anxiety in fragile X syndrome

Individuals with fragile X syndrome (FXS) commonly display characteristics of social anxiety, including gaze aversion, increased time to initiate social interaction, and difficulty forming meaningful peer relationships. While neural correlates of face processing, an important component of social interaction, are altered in FXS, studies have not examined whether social anxiety in this population is related to higher cognitive processes, such as memory. This study aimed to determine whether the neural circuitry involved in face encoding was disrupted in individuals with FXS, and whether brain activity during face encoding was related to levels of social anxiety. A group of 11 individuals with FXS (5 M) and 11 age- and gender-matched control participants underwent fMRI scanning while performing a face encoding task with online eye-tracking. Results indicate that compared to the control group, individuals with FXS exhibited decreased activation of prefrontal regions associated with complex social cognition, including the medial and superior frontal cortex, during successful face encoding. Further, the FXS and control groups showed significantly different relationships between measures of social anxiety (including gaze-fixation) and brain activity during face encoding. These data indicate that social anxiety in FXS may be related to the inability to successfully recruit higher level social cognition regions during the initial phases of memory formation.

Preoperative amygdala fMRI in temporal lobe epilepsy

Purpose:

Anterior temporal lobe resections (ATLR) benefit 70% of patients with refractory mesial temporal lobe epilepsy (TLE), but may be complicated by emotional disturbances. We used functional magnetic resonance imaging (fMRI) to investigate the role of the amygdala in processing emotions in TLE and whether this may be a potential preoperative predictive marker for emotional disturbances following surgery.

Methods:

We studied 54 patients with refractory mesial TLE due to hippocampal sclerosis (28 right, 26 left) and 21 healthy controls using a memory encoding fMRI paradigm, which included viewing fearful and neutral faces. Twenty-one TLE patients (10 left, 11 right) subsequently underwent ATLR. Anxiety and depression were assessed preoperatively and 4 months postoperatively using the Hospital Anxiety and Depression Scale.

Results:

On viewing fearful faces, healthy controls demonstrated left lateralized, while right TLE patients showed bilateral amygdala activation. Left TLE patients had significantly reduced activation in left and right amygdalae compared to controls and right TLE patients. In right TLE patients, left and right amygdala activation was significantly related to preoperative anxiety and depression levels, and preoperative right amygdala activation correlated significantly with postoperative change of anxiety and depression scores, characterized by greater increases in anxiety and depression in patients with greater preoperative activation. No such correlations were seen for left TLE patients.

Discussion:

The fearful face fMRI paradigm is a reliable method for visualizing amygdala activation in controls and patients with mesial TLE. Activation of the right amygdala preoperatively was predictive of emotional disturbances following right ATLR.

Effects of semantic relatedness on recall of stimuli preceding emotional oddballs

Semantic and episodic memory networks function as highly interconnected systems, both relying on the hippocampal/medial temporal lobe complex (HC/MTL). Episodic memory encoding triggers the retrieval of semantic information, serving to incorporate contextual relationships between the newly acquired memory and existing semantic representations. While emotional material augments episodic memory encoding at the time of stimulus presentation, interactions between emotion and semantic memory that contribute to subsequent episodic recall are not well understood. Using a modified oddball task, we examined the modulatory effects of negative emotion on semantic interactions with episodic memory by measuring the free-recall of serially presented neutral or negative words varying in semantic relatedness. We found increased free-recall for words related to and preceding emotionally negative oddballs, suggesting that negative emotion can indirectly facilitate episodic free-recall by enhancing semantic contributions during encoding. Our findings demonstrate the ability of emotion and semantic memory to interact to mutually enhance free-recall.

The influence of personality on neural mechanisms of observational fear and reward learning

Fear and reward learning can occur through direct experience or observation. Both channels can enhance survival or create maladaptive behavior. We used fMRI to isolate neural mechanisms of observational fear and reward learning and investigate whether neural response varied according to individual differences in neuroticism and extraversion. Participants learned object-emotion associations by observing a woman respond with fearful (or neutral) and happy (or neutral) facial expressions to novel objects. The amygdala-hippocampal complex was active when learning the object-fear association, and the hippocampus was active when learning the object-happy association. After learning, objects were presented alone; amygdala activity was greater for the fear (vs. neutral) and happy (vs. neutral) associated object. Importantly, greater amygdala-hippocampal activity during fear (vs. neutral) learning predicted better recognition of learned objects on a subsequent memory test. Furthermore, personality modulated neural mechanisms of learning. Neuroticism positively correlated with neural activity in the amygdala and hippocampus during fear (vs. neutral) learning. Low extraversion/high introversion was related to faster behavioral predictions of the fearful and neutral expressions during fear learning. In addition, low extraversion/high introversion was related to greater amygdala activity during happy (vs. neutral) learning, happy (vs. neutral) object recognition, and faster reaction times for predicting happy and neutral expressions during reward learning. These findings suggest that neuroticism is associated with an increased sensitivity in the neural mechanism for fear learning which leads to enhanced encoding of fear associations, and that low extraversion/high introversion is related to enhanced conditionability for both fear and reward learning.

MDMA induces EPSP-Spike potentiation in rat ventral hippocampus in vitro via serotonin and noradrenaline release and coactivation of 5-HT4 and beta1 receptors

It is well documented that N-methyl-3,4-methylenedioxyamphetamine (MDMA, ecstasy) releases brain serotonin (5-HT; 5-hydroxytryptamine), noradrenaline (NE; norepinephrine), and dopamine, but the consequent effect on brain functioning remains elusive. In this study, we characterized the effects of MDMA on electrically evoked responses in the ventral CA1 region of a rat hippocampal slice preparation. Superfusion with MDMA (10 microM, 30 min) increased the population spike amplitude (PSA) by 48.9+/-31.2% and decreased population spike latency (PSL) by 103+/-139 mus (both: mean+/-SD, n=123; p<0.0001, Wilcoxon test), without affecting field excitatory postsynaptic potential (fEPSP). This effect persisted for at least 1 h after MDMA washout; we have called this EPSP-spike potentiation (ESP) by MDMA, ESP MDMA. Antagonism of GABAergic transmission did not prevent ESP MDMA, suggesting that an increase in excitability of pyramidal cells underlies this MDMA action. Block of serotonin transporter (SERT) with citalopram or 5-HT depletion with (+/-)-p-chlorophenylalanine pretreatment partially inhibited the ESP MDMA. Block of both SERT and NE transporter prevented ESP MDMA, indicating its dependence on release of both 5-HT and NE. ESP MDMA is produced by simultaneous activation of 5-HT4 and beta1 receptors, with a predominant role of 5-HT4 receptors. Block of both 5-HT4 and beta1 receptors revealed an inhibitory component of the MDMA action mediated by 5-HT1A receptor. The concentration range of MDMA which produced ESP MDMA (1-30 microM) corresponds to that commonly reached in human plasma following the ingestion of psychoactive MDMA doses, suggesting that release of both 5-HT and NE, and consequent ESP MDMA may underlie some of the psychoactive effects of MDMA in humans.

Emotional perception modulated by an opioid and a cholecystokinin agonist

RATIONALE

The cholecystokinin (CCK) and opioid neuromodulatory systems work in an antagonistic fashion and can modulate emotional states and noxious input in opposite directions. In this behavioral study, we generalize this idea and suggest that CCK and opioids can modulate the processing of other external signals, e.g., visual stimuli rather than only noxious input.

OBJECTIVES

The objective of this study was to determine whether CCK and an opioid agonist could modulate the emotional experience of visual stimuli.

MATERIALS AND METHODS

Thirteen healthy male volunteers viewed standardized pictures with either neutral or unpleasant content. Simultaneously, one of three treatments was administered in a randomized, double-blind crossover design: the CCKb receptor agonist pentagastrin (0.1 microg/kg), the mu-opioid receptor agonist remifentanil (0.0625 microg/kg), or saline. Self-ratings of the emotional experience of pictures and drugs were sampled together with psychological tests and recording of heart rate.

RESULTS

Pentagastrin treatment increased the rating of unpleasantness for both neutral and unpleasant pictures, while it decreased the rating of pleasantness for the neutral pictures. These effects did not correlate with the degree of general unpleasantness induced by the drug. Remifentanil treatment increased the pleasantness for the neutral pictures. While pentagastrin treatment induced a heart rate increase, unpleasant pictures induced a heart rate decrease, and the magnitude of change in heart rate correlated positively for these conditions.

CONCLUSIONS

This study shows that the CCK and the opioid system modulate how external stimuli are emotionally perceived, suggesting a possible involvement in affective disorders.

Role of amygdala connectivity in the persistence of emotional memories over time: an event-related FMRI investigation

According to the consolidation hypothesis, enhanced memory for emotional information reflects the modulatory effect of the amygdala on the medial temporal lobe (MTL) memory system during consolidation. Although there is evidence that amygdala-MTL connectivity enhances memory for emotional stimuli, it remains unclear whether this enhancement increases over time, as consolidation processes unfold. To investigate this, we used functional magnetic resonance imaging to measure encoding activity predicting memory for emotionally negative and neutral pictures after short (20-min) versus long (1-week) delays. Memory measures distinguished between vivid remembering (recollection) and feelings of knowing (familiarity). Consistent with the consolidation hypothesis, the persistence of recollection over time (long divided by short) was greater for emotional than neutral pictures. Activity in the amygdala predicted subsequent memory to a greater extent for emotional than neutral pictures. Although this advantage did not vary with delay, the contribution of amygdala-MTL connectivity to subsequent memory for emotional items increased over time. Moreover, both this increase in connectivity and amygdala activity itself were correlated with individual differences in recollection persistence for emotional but not neutral pictures. These results suggest that the amygdala and its connectivity with the MTL are critical to sustaining emotional memories over time, consistent with the consolidation hypothesis.

Immediate memory consequences of the effect of emotion on attention to pictures

Emotionally arousing stimuli are at once both highly attention grabbing and memorable. We examined whether emotional enhancement of memory (EEM) reflects an indirect effect of emotion on memory, mediated by enhanced attention to emotional items during encoding. We tested a critical prediction of the mediation hypothesis-that regions conjointly activated by emotion and attention would correlate with subsequent EEM. Participants were scanned with fMRI while they watched emotional or neutral pictures under instructions to attend to them a lot or a little, and were then given an immediate recognition test. A region in the left fusiform gyrus was activated by emotion, voluntary attention, and subsequent EEM. A functional network, different for each attention condition, connected this region and the amygdala, which was associated with emotion and EEM, but not with voluntary attention. These findings support an indirect cortical mediation account of immediate EEM that may complement a direct modulation model.

The amygdala modulates neuronal activation in the hippocampus in response to spatial novelty

Emerging evidence indicates that the amygdala and the hippocampus play an important role in the pathophysiology of major psychotic disorders. Consistent with this evidence, and with data indicating amygdala modulation of hippocampal activity, animal model investigations have shown that a disruption of amygdala activity induces neurochemical changes in the hippocampus that are similar to those detected in subjects with schizophrenia. With the present study, we used induction of the immediate early gene Fos, to test the hypothesis that the amygdala may affect neuronal activation of the hippocampus in response to different spatial environments (familiar, modified, and novel). Exploratory and anxiety related behaviors were also assessed. In vehicle-treated rats, exposure to a modified version of the familiar environment was associated with an increase of numerical densities of Fos-immunoreactive nuclei in sectors CA1 and CA2, while exposure to a completely novel environment was associated with an increase in sectors CA1, CA4, and DG, compared with the familiar environment. Pharmacological disruption of amygdala activity resulted in a failure to increase Fos induction in the hippocampus in response to these environments. Exploratory behavior in response to the different environments was not altered by manipulation of amygdala activity. These findings support the idea that the amygdala modulates spatial information processing in the hippocampus and may affect encoding of specific environmental features, while complex behavioral responses to environment may be the result of broader neural circuits. These findings also raise the possibility that amygdala abnormalities may contribute to impairments in cognitive information processing in subjects with major psychoses.

Noradrenergic-glucocorticoid mechanisms in emotion-induced amnesia: from adaptation to disease

DISCUSSIONS

The interaction of emotion and episodic encoding has costs and benefits. These costs and benefits have been characterized in oddball experiments, where a violation of prevailing neutral context through aversive oddballs is associated with subsequent hypermnesia for the aversive oddball and peri-emotional amnesia for the neutral context. Both hypermnesia and peri-emotional amnesia are amygdala-dependent and vary as a function of noradrenergic-glucocorticoid input to the amygdala during emotional episodic encoding. Pharmacological enhancement of this input allows to model the maladaptive effects of emotion on episodic encoding. Extrapolation of these findings to conditions of emotional trauma suggests that disinhibited noradrenergic-glucocorticoid signaling could serve as a crucial etiological contributor to the pathogenesis of peri-traumatic amnesia (PTA) and post-traumatic stress disorder (PTSD).

CONCLUSIONS

Immediate pharmacological blockade of noradrenergic-glucocorticoid signaling might prove effective in the secondary prevention of PTA and PTSD.

Emotional memory function, personality structure and psychopathology: a neural system approach to the identification of vulnerability markers

It is well established that emotional events are ingrained stronger into memory relative to neutral events. Facilitated emotional memory is highly variable between individuals within the normal population and is particularly exacerbated in those diagnosed with mood and anxiety disorders. In order to elucidate how variation of enhanced emotional memory within the normal population may manifest into psychopathological states, we explored the convergence between studies investigating the neural systems engaged in emotional memory facilitation and studies investigating how these systems differ from person to person. Converging evidence highlights the roles of three neural systems (1. Amygdala function and attention, 2. Neuroendocrine function, 3. Interactive effects with mood) that all govern emotional memory facilitation and are highly variable between individuals as a function of personality. We applied this neural system approach to models of vulnerability of three forms of psychopathology that are particularly characterized by atypical emotional memory function (depression, generalized anxiety disorder and post-traumatic stress disorder). This application suggests that the incorporation of known vulnerability markers across psychological, neuroimaging and neuroendocrinological domains is cardinal to how susceptibility is conceptualized and assessed in these disorders.

Steroid abnormalities and the developing brain: declarative memory for emotionally arousing and neutral material in children with congenital adrenal hyperplasia

Steroid hormones modulate memory in animals and human adults. Little is known on the developmental effects of these hormones on the neural networks underlying memory. Using Congenital adrenal hyperplasia (CAH) as a naturalistic model of early steroid abnormalities, this study examines the consequences of CAH on memory and its neural correlates for emotionally arousing and neutral material in children. Seventeen patients with CAH and 17 age- and sex-matched healthy children (ages 12-14 years) completed the study. Subjects were presented positive, negative and neutral pictures. Memory recall occurred about 30min after viewing the pictures. Children with CAH showed memory deficits for negative pictures compared to healthy children (p<0.01). There were no group differences on memory performance for either positive or neutral pictures (p>0.1). In patients, 24h urinary-free cortisol levels (reflecting glucocorticoid replacement therapy) and testosterone levels were not associated with memory performance. These findings suggest that early steroid imbalances affect memory for negative material in children with CAH. Such memory impairments may result from abnormal brain organization and function following hormonal dysfunction during critical periods of development.

EphB receptors regulate stem/progenitor cell proliferation, migration, and polarity during hippocampal neurogenesis

The adult brain maintains two regions of neurogenesis from which new neurons are born, migrate to their appropriate location, and become incorporated into the circuitry of the CNS. One of these, the subgranular zone of the hippocampal dentate gyrus, is of primary interest because of the role of this region in learning and memory. We show that mice lacking EphB1, and more profoundly EphB1 and EphB2, have significantly fewer neural progenitors in the hippocampus. Furthermore, other aspects of neurogenesis, such as polarity, cell positioning, and proliferation are disrupted in animals lacking the EphB1 receptor or its cognate ephrin-B3 ligand. Our data strongly suggest that EphB1 and ephrin-B3 cooperatively regulate the proliferation and migration of neural progenitors in the hippocampus and should be added to a short list of candidate target molecules for modulating the production and integration of new neurons as a treatment for neurodegenerative diseases or brain injury.

How progesterone impairs memory for biologically salient stimuli in healthy young women

Progesterone, or rather its neuroactive metabolite allopregnanolone, modulates amygdala activity and thereby influences anxiety. Cognition and, in particular, memory are also altered by allopregnanolone. In the present study, we investigated whether allopregnanolone modulates memory for biologically salient stimuli by influencing amygdala activity, which in turn may affect neural processes in other brain regions. A single progesterone dose was administered orally to healthy young women in a double-blind, placebo-controlled, crossover design, and participants were asked to memorize and recognize faces while undergoing functional magnetic resonance imaging. Progesterone decreased recognition accuracy without affecting reaction times. The imaging results show that the amygdala, hippocampus, and fusiform gyrus supported memory formation. Importantly, progesterone decreased responses to faces in the amygdala and fusiform gyrus during memory encoding, whereas it increased hippocampal responses. The progesterone-induced decrease in neural activity in the amygdala and fusiform gyrus predicted the decrease in memory performance across subjects. However, progesterone did not modulate the differential activation between subsequently remembered and subsequently forgotten faces in these areas. A similar pattern of results was observed in the fusiform gyrus and prefrontal cortex during memory retrieval. These results suggest that allopregnanolone impairs memory by reducing the recruitment of those brain regions that support memory formation and retrieval. Given the important role of the amygdala in the modulation of memory, these results suggest that allopregnanolone alters memory by influencing amygdala activity, which in turn may affect memory processes in other brain regions.

A functional MRI study of happy and sad affective states induced by classical music

The present study investigated the functional neuroanatomy of transient mood changes in response to Western classical music. In a pilot experiment, 53 healthy volunteers (mean age: 32.0; SD = 9.6) evaluated their emotional responses to 60 classical musical pieces using a visual analogue scale (VAS) ranging from 0 (sad) through 50 (neutral) to 100 (happy). Twenty pieces were found to accurately induce the intended emotional states with good reliability, consisting of 5 happy, 5 sad, and 10 emotionally unevocative, neutral musical pieces. In a subsequent functional magnetic resonance imaging (fMRI) study, the blood oxygenation level dependent (BOLD) signal contrast was measured in response to the mood state induced by each musical stimulus in a separate group of 16 healthy participants (mean age: 29.5; SD = 5.5). Mood state ratings during scanning were made by a VAS, which confirmed the emotional valence of the selected stimuli. Increased BOLD signal contrast during presentation of happy music was found in the ventral and dorsal striatum, anterior cingulate, parahippocampal gyrus, and auditory association areas. With sad music, increased BOLD signal responses were noted in the hippocampus/amygdala and auditory association areas. Presentation of neutral music was associated with increased BOLD signal responses in the insula and auditory association areas. Our findings suggest that an emotion processing network in response to music integrates the ventral and dorsal striatum, areas involved in reward experience and movement; the anterior cingulate, which is important for targeting attention; and medial temporal areas, traditionally found in the appraisal and processing of emotions.

How emotion strengthens the recollective experience: a time-dependent hippocampal process

Emotion significantly strengthens the subjective recollective experience even when objective accuracy of the memory is not improved. Here, we examine if this modulation is related to the effect of emotion on hippocampal-dependent memory consolidation. Two critical predictions follow from this hypothesis. First, since consolidation is assumed to take time, the enhancement in the recollective experience for emotional compared to neutral memories should become more apparent following a delay. Second, if the emotion advantage is critically dependent on the hippocampus, then the effects should be reduced in amnesic patients with hippocampal damage. To test these predictions we examined the recollective experience for emotional and neutral photos at two retention intervals (Experiment 1), and in amnesics and controls (Experiment 2). Emotional memories were associated with an enhancement in the recollective experience that was greatest after a delay, whereas familiarity was not influenced by emotion. In amnesics with hippocampal damage the emotion effect on recollective experience was reduced. Surprisingly, however, these patients still showed a general memory advantage for emotional compared to neutral items, but this effect was manifest primarily as a facilitation of familiarity. The results support the consolidation hypothesis of recollective experience, but suggest that the effects of emotion on episodic memory are not exclusively hippocampally mediated. Rather, emotion may enhance recognition by facilitating familiarity when recollection is impaired due to hippocampal damage.

The coupling of emotion and cognition in the eye: Introducing the pupil old/new effect

The study presented here investigated the effects of emotional valence on the memory for words by assessing both memory performance and pupillary responses during a recognition memory task. Participants had to make speeded judgments on whether a word presented in the test phase of the experiment had already been presented ("old") or not ("new"). An emotion-induced recognition bias was observed: Words with emotional content not only produced a higher amount of hits, but also elicited more false alarms than neutral words. Further, we found a distinct pupil old/new effect characterized as an elevated pupillary response to hits as opposed to correct rejections. Interestingly, this pupil old/new effect was clearly diminished for emotional words. We therefore argue that the pupil old/new effect is not only able to mirror memory retrieval processes, but also reflects modulation by an emotion-induced recognition bias.

Gamma oscillations coordinate amygdalo-rhinal interactions during learning

The rhinal cortices contribute to memory formation by integrating and transferring neocortical information to the hippocampus. Rhinal contributions to memory are likely influenced by the amygdala because strong reciprocal connections exist between these structures. In light of previous data showing that oscillations regulate neuronal activity during memory formation and recall, we tested the possibility that coherent oscillations serve to coordinate amygdalo-rhinal activity during learning. To this end, we performed simultaneous extracellular recordings of basolateral amygdala (BLA), perirhinal, and entorhinal activity. We first tested whether there are correlated fluctuations in the power of BLA and rhinal field activity during the waking state. Correlated power fluctuations were most pronounced in the 35-45 Hz band. Within each structure, firing probability fluctuated rhythmically with the fast oscillations, indicating that they were not volume conducted. To test whether fast oscillations coordinate BLA and rhinal activity during learning, animals were trained on a trace-conditioning task in which a visual conditioned stimulus (CS) predicted a food reward after a delay. The predictive value of the CS was learned gradually over 9 d. As learning progressed, the 35-45 Hz power increased in the BLA and rhinal cortices, particularly during the late part of the CS and delay. Moreover, the firing of BLA and rhinal neurons became rhythmically entrained by BLA oscillations at that time. Thus, our data suggest that neuronal interactions are coordinated by fast oscillations in the BLA-rhinal network. By telescoping the periods of effective neuronal interactions in short recurring time windows, these fast oscillations may facilitate rhinal interactions and synaptic plasticity.

Physiology and neurobiology of stress and adaptation: central role of the brain

The brain is the key organ of the response to stress because it determines what is threatening and, therefore, potentially stressful, as well as the physiological and behavioral responses which can be either adaptive or damaging. Stress involves two-way communication between the brain and the cardiovascular, immune, and other systems via neural and endocrine mechanisms. Beyond the "flight-or-fight" response to acute stress, there are events in daily life that produce a type of chronic stress and lead over time to wear and tear on the body ("allostatic load"). Yet, hormones associated with stress protect the body in the short-run and promote adaptation ("allostasis"). The brain is a target of stress, and the hippocampus was the first brain region, besides the hypothalamus, to be recognized as a target of glucocorticoids. Stress and stress hormones produce both adaptive and maladaptive effects on this brain region throughout the life course. Early life events influence life-long patterns of emotionality and stress responsiveness and alter the rate of brain and body aging. The hippocampus, amygdala, and prefrontal cortex undergo stress-induced structural remodeling, which alters behavioral and physiological responses. As an adjunct to pharmaceutical therapy, social and behavioral interventions such as regular physical activity and social support reduce the chronic stress burden and benefit brain and body health and resilience.

Alcohol: effects on neurobehavioral functions and the brain

Alcoholism results from an interplay between genetic and environmental factors, and is linked to brain defects and associated cognitive, emotional, and behavioral impairments. A confluence of findings from neuroimaging, physiological, neuropathological, and neuropsychological studies of alcoholics indicate that the frontal lobes, limbic system, and cerebellum are particularly vulnerable to damage and dysfunction. An integrative approach employing a variety of neuroscientific technologies is essential for recognizing the interconnectivity of the different functional systems affected by alcoholism. In that way, relevant experimental techniques can be applied to assist in determining the degree to which abstinence and treatment contribute to the reversal of atrophy and dysfunction.

Enhanced emotion-induced amnesia in borderline personality disorder

BACKGROUND

Current biological concepts of borderline personality disorder (BPD) emphasize the interference of emotional hyperarousal and cognitive functions. A prototypical example is episodic memory. Pre-clinical investigations of emotion-episodic memory interactions have shown specific retrograde and anterograde episodic memory changes in response to emotional stimuli. These changes are amygdala dependent and vary as a function of emotional arousal and valence.

METHOD

To determine whether there is amygdala hyper-responsiveness to emotional stimuli as the underlying pathological substrate of cognitive dysfunction in BPD, 16 unmedicated female patients with BPD were tested on the behavioural indices of emotion-induced amnesia and hypermnesia established in 16 healthy controls.

RESULTS

BPD patients displayed enhanced retrograde and anterograde amnesia in response to presentation of negative stimuli, while positive stimuli elicited no episodic memory-modulating effects.

CONCLUSION

These findings suggest that an amygdala hyper-responsiveness to negative stimuli may serve as a crucial aetiological contributor to emotion-induced cognitive dysfunction in BPD.

Genetic architecture of fear conditioning in chromosome substitution strains: relationship to measures of innate (unlearned) anxiety-like behavior

We measured fear conditioning (FC) in a panel of chromosome substitution strains (CSS) created using the C57BL/6J (B6) and A/J (AJ) inbred strains. Mice were trained to associate a specific context and tone with a foot shock. FC was measured by observing freezing behavior during re-exposure to the context and tone. Freezing to context was more than twofold greater in the AJ strain relative to the B6 strain. Among the CSS we identified four strains with higher (CSS-6, -10, -11, and -18) and two strains with lower (CSS-7 and -14) freezing to context. CSS-10 and -18 also showed higher freezing to tone, while CSS-12 showed less freezing to tone. CSS-1 has been implicated in open-field (OF) and light-dark box (LDB); we observed significant activity differences prior to training but no differences in FC. Chromosomes 6 and 10 have been associated with differences in anxiety-like behaviors, suggesting the existence of pleiotropic alleles that influence both learned and innate fear. By utilizing a genetic reference population, we have identified chromosomes that pleiotropically influence multiple phenotypes hypothesized to reflect a common ethologic construct that has been termed emotionality. The CSS provide a straightforward means of isolating the underlying genetic factors.

Cross-validating the Berlin Affective Word List

We introduce the Berlin Affective Word List (BAWL) in order to provide researchers with a German database containing both emotional valence and imageability ratings for more than 2,200 German words. The BAWL was cross-validated using a forced choice valence decision task in which two distinct valence categories (negative or positive) had to be assigned to a highly controlled selection of 360 words according to varying emotional content (negative, neutral, or positive). The reaction time (RT) results corroborated the valence categories: Words that had been rated as "neutral" in the norms yielded maximum RTs. The BAWL is intended to help researchers create stimulus materials for a wide range of experiments dealing with the emotional processing of words.

D-cycloserine reduces neuropathic pain behavior through limbic NMDA-mediated circuitry

Human brain imaging studies suggest that chronic neuropathic pain has a strong emotional component that is mediated by medial prefrontal cortex (mPFC) activity; in rodents, the mPFC is involved in emotional and cognitive aspects of behavior, including the extinction of Pavlovian fear conditioning. Together, these findings suggest that the cortex may modulate the memory trace of pain. As D-cycloserine (DCS), a partial agonist of the NMDA receptor, can enhance learning and potentiate the extinction of acquired fear, in the present study we tested its efficacy in neuropathic pain behavior. In rats with spared nerve injury (SNI), repeated daily oral administration of DCS reduced mechanical sensitivity of the injured limb in a dose-dependent manner; this effect continued for weeks after the cessation of DCS treatment. In addition, re-exposure to DCS further enhanced antinociceptive behavior. Repeated oral DCS administration also reduced cancer chemotherapy drug-induced neuropathic pain behavior. Infusions of DCS directly into the mPFC (especially within prelimbic cortex) or the amygdala (but not into thalamus, insula, or occipital cortex) acutely induced antinociception in SNI rats. The antinociceptive effect of intra-mPFC DCS infusions was mimicked by NMDA and glycine, and blocked by HA 966. In the mPFC of SNI rats, NR2B expression was down-regulated; however, this effect was reversed with repeated oral DCS. Lastly, infusions of DCS into mPFC reversed place avoidance behavior induced by mechanical stimulation of the injured paw in SNI rats. These findings indicate that limbic NMDA-mediated circuitry is involved in long-term reduction in neuropathic pain behavior.

Dissociated theta phase synchronization in amygdalo- hippocampal circuits during various stages of fear memory

The amygdala and the hippocampus are critically involved in the formation and retention of fear memories. However, their precise contribution to, and their interplay during, fear memory formation are not fully understood. In the present study we investigated network activities in the amygdalo-hippocampal system of freely behaving mice at different stages of fear memory consolidation and retention. Our data show enhanced theta phase synchronization in this pathway during the retrieval of fear memory at long-term (24 h post-training), but not short-term (2 min, 30 min and 2 h post-training) stages, following both contextual and auditory cued conditioning. However, retrieval of remotely conditioned fear (30 days post-training) failed to induce an increase in synchronization despite there still being memory retention. Thus, our data indicate that the amygdalo-hippocampal interaction reflects a dynamic interaction of ensemble activities related to various stages of fear memory consolidation and/or retention, and support the notion that recent and remote memories are organized through different network principles.