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

Active exploration of an environment drives the activation of the hippocampus-amygdala complex of domestic chicks

In birds, like in mammals, the hippocampus critically mediates spatial navigation through the formation of a spatial map. This study investigates the impact of active exploration of an environment on the hippocampus of young domestic chicks. Chicks that were free to actively explore the environment exhibited a significantly higher neural activation (measured by c-Fos expression), compared to those that passively observed the same environment from a restricted area. The difference was limited to the anterior and the dorsolateral parts of the intermediate hippocampus. Furthermore, the nucleus taeniae of the amygdala showed a higher c-Fos expression in the active exploration group than the passive observation group. In both brain regions, brain activation correlated with the number of locations that chicks visited during the test. This suggest that the increase of c-Fos expression in the hippocampus is related to increased firing rates of spatially coding neurons. Furthermore, our study indicates a functional linkage of the hippocampus and nucleus taeniae of the amygdala in processing spatial information. Overall, with the present study, we confirm that, in birds like in mammals, hippocampus and amygdala functions are linked and likely related to spatial representations.

Response Flexibility: The Role of the Lateral Habenula

The ability to make appropriate decisions that result in an optimal outcome is critical for survival. This process involves assessing the environment as well as integrating prior knowledge about the environment with information about one's current internal state. There are many neural structures that play critical roles in mediating these processes, but it is not yet known how such information coalesces to influence behavioral output. The lateral habenula (LHb) has often been cited as a structure critical for adaptive and flexible responding when environmental contexts and internal state changes. A challenge, however, has been understanding how LHb promotes response flexibility. In this review, we hypothesize that the LHb enables flexible responding following the integration of context memory and internal state information by signaling downstream brainstem structures known to drive hippocampal theta. In this way, animals respond more flexibly in a task situation not because the LHb selects a particular action, but rather because LHb enhances a hippocampal neural state that is often associated with greater attention, arousal, and exploration. In freely navigating animals, these are essential conditions that are needed to discover and implement appropriate alternative choices and behaviors. As a corollary to our hypothesis, we describe short- and intermediate-term functions of the LHb. Finally, we discuss the effects on the behavior of LHb dysfunction in short- and intermediate-timescales, and then suggest that new therapies may act on the LHb to alleviate the behavioral impairments following long-term LHb disruption.

Functional coupling between CA3 and laterobasal amygdala supports schema dependent memory formation

The medial temporal lobe drives semantic congruence dependent memory formation. However, the exact roles of hippocampal subfields and surrounding brain regions remain unclear. Here, we used an established paradigm and high-resolution functional magnetic resonance imaging of the medial temporal lobe together with cytoarchitectonic probability estimates in healthy humans. Behaviorally, robust congruence effects emerged in young and older adults, indicating that schema dependent learning is unimpaired during healthy aging. Within the medial temporal lobe, semantic congruence was associated with hemodynamic activity in the subiculum, CA1, CA3 and dentate gyrus, as well as the entorhinal cortex and laterobasal amygdala. Importantly, a subsequent memory analysis showed increased activity for later remembered vs. later forgotten congruent items specifically within CA3, and this subfield showed enhanced functional connectivity to the laterobasal amygdala. As such, our findings extend current models on schema dependent learning by pinpointing the functional properties of subregions within the medial temporal lobe.

Control of parallel hippocampal output pathways by amygdalar long-range inhibition

Projections from the basal amygdala (BA) to the ventral hippocampus (vH) are proposed to provide information about the rewarding or threatening nature of learned associations to support appropriate goal-directed and anxiety-like behaviour. Such behaviour occurs via the differential activity of multiple, parallel populations of pyramidal neurons in vH that project to distinct downstream targets, but the nature of BA input and how it connects with these populations is unclear. Using channelrhodopsin-2-assisted circuit mapping in mice, we show that BA input to vH consists of both excitatory and inhibitory projections. Excitatory input specifically targets BA- and nucleus accumbens-projecting vH neurons and avoids prefrontal cortex-projecting vH neurons, while inhibitory input preferentially targets BA-projecting neurons. Through this specific connectivity, BA inhibitory projections gate place-value associations by controlling the activity of nucleus accumbens-projecting vH neurons. Our results define a parallel excitatory and inhibitory projection from BA to vH that can support goal-directed behaviour.

Noradrenergic circuits in the forebrain control affective responses to novelty

RATIONALE

In rodents, exposure to novel environments elicits initial anxiety-like behavior (neophobia) followed by intense exploration (neophilia) that gradually subsides as the environment becomes familiar. Thus, innate novelty-induced behaviors are useful indices of anxiety and motivation in animal models of psychiatric disease. Noradrenergic neurons are activated by novelty and implicated in exploratory and anxiety-like responses, but the role of norepinephrine (NE) in neophobia has not been clearly delineated.

OBJECTIVE

We sought to define the role of central NE transmission in neophilic and neophobic behaviors.

METHODS

We assessed dopamine β-hydroxylase knockout (Dbh -/-) mice lacking NE and their NE-competent (Dbh +/-) littermate controls in neophilic (novelty-induced locomotion; NIL) and neophobic (novelty-suppressed feeding; NSF) behavioral tests with subsequent quantification of brain-wide c-fos induction. We complimented the gene knockout approach with pharmacological interventions.

RESULTS

Dbh -/- mice exhibited blunted locomotor responses in the NIL task and completely lacked neophobia in the NSF test. Neophobia was rescued in Dbh -/- mice by acute pharmacological restoration of central NE with the synthetic precursor L-3,4-dihydroxyphenylserine (DOPS), and attenuated in control mice by the inhibitory α2-adrenergic autoreceptor agonist guanfacine. Following either NSF or NIL, Dbh -/- mice demonstrated reduced c-fos in the anterior cingulate cortex, medial septum, ventral hippocampus, bed nucleus of the stria terminalis, and basolateral amygdala.

CONCLUSION

These findings indicate that central NE signaling is required for the expression of both neophilic and neophobic behaviors. Further, we describe a putative noradrenergic novelty network as a potential therapeutic target for treating anxiety and substance abuse disorders.

The effect of monocular occlusion on hippocampal c-Fos expression in domestic chicks (Gallus gallus)

In birds, like in mammals, the hippocampus is particularly sensitive to exposure to novel environments, a function that is based on visual input. Chicks' eyes are placed laterally and their optic fibers project mainly to the contralateral brain hemispheres, with only little direct interhemispheric coupling. Thus, monocular occlusion has been frequently used in chicks to document functional specialization of the two hemispheres. However, we do not know whether monocular occlusion influences hippocampal activation. The aim of the present work was to fill this gap by directly testing this hypothesis. To induce hippocampal activation, chicks were exposed to a novel environment with their left or right eye occluded, or in conditions of binocular vision. Their hippocampal expression of c-Fos (neural activity marker) was compared to a baseline group that remained in a familiar environment. Interestingly, while the hippocampal activation in the two monocular groups was not different from the baseline, it was significantly higher in the binocular group exposed to the novel environment. This suggest that the representation of environmental novelty in the hippocampus of domestic chicks involves strong binocular integration.

Abnormal Subcortical Volumes and Cortical Thickness in Parkinson's Disease with Impulse Control Disorders

Background

The occurrence of impulse control disorders (ICDs) in Parkinson's disease (PD) is frequently attributed to dopamine replacement therapy. However, not all patients who receive medication develop ICDs. Recent imaging studies have suggested specific neuroanatomical abnormalities in patients with PD and ICD.

Objectives

This study aims to identify changes in volumes of subcortical structures and cortical thickness specific to patients with PD and ICDs.

Methodology

A total of 11 patients with PD and ICD (PD_ICD(+)), 15 patients with PD without ICD (PD_ICD(-)), and 15 healthy controls were analyzed in this study. ICDs were diagnosed and quantified using the Questionnaire for Impulsive-Compulsive Disorders in PD-Rating Scale (QUIP-RS). Structural imaging was performed on a 3T scanner; volumes of subcortical structures and cortical thickness were obtained using first in FSL and FreeSurfer.

Results

Significant volume loss of the nucleus accumbens was observed in the PD_ICD(+) group. Several areas of significant cortical thinning were observed in the PD_ICD(+) group in comparison PD_ICD(-) group. Thinning of the left middle temporal gyrus, transverse temporal gyrus, and bilateral temporal poles was observed in the PD_ICD(+) group. No correlations were observed between QUIP-RS scores and areas of cortical thinning.

Conclusions

The PD_ICD(+) group has specific neuroanatomical variations in the nucleus accumbens and temporal lobes, which may contribute to the development of ICD and perhaps predispose a patient to ICDs on exposure to dopamine replacement therapy.

Adrenergic β receptor activation in the basolateral amygdala, which is intracellular Zn2+-dependent, rescues amyloid β1-42-induced attenuation of dentate gyrus LTP

On the basis of the evidence that the basolateral amygdala (BLA) modulates hippocampal memory processes via synaptic plasticity, here we report that adrenergic β receptor activation in the BLA rescues amyloid β_1-42 (Aβ_1-42)-induced attenuation of long-term potentiation (LTP) at perforant pathway-dentate granule cell (DGC) synapses. When 500 μM isoproterenol (2 μl), an adrenergic β receptor agonist, was injected into the BLA 20 min before LTP induction, LTP was enhanced. Isoproterenol-mediated enhancement of LTP was blocked by co-injection with 100 μM ZnAF-2DA, an intracellular Zn²⁺ chelator, suggesting that intracellular Zn²⁺ is required for the intracellular signaling cascade after adrenergic β receptor activation in the BLA. Aβ_1-42-induced attenuation of LTP, which was induced by Aβ_1-42 injection into the dentate gyrus 60 min before LTP induction, was rescued by isoproterenol injection into the BLA 20 min before LTP induction, but not by 500 μM phenylephrine (2 μl), an adrenergic α₁ receptor agonist, injection into the BLA, which did not enhance LTP unlike the case of isoproterenol injection. Interestingly, Aβ_1-42-induced attenuation of LTP was also rescued by 100 μM isoproterenol injection into the BLA 20 min before LTP induction, which did not enhance LTP. The present study demonstrates that adrenergic β receptor activation in the BLA, which is linked with intracellular Zn²⁺ signaling, rescues Aβ_1-42-induced attenuation of dentate gyrus LTP. It is likely that adrenergic β receptor activation in the BLA is a strategy for rescuing Aβ_1-42-induced cognitive decline that is associated with hippocampal synaptic plasticity.

Experience-dependent shaping of hippocampal CA1 intracellular activity in novel and familiar environments

The hippocampus is critical for producing stable representations of familiar spaces. How these representations arise is poorly understood, largely because changes to hippocampal inputs have not been measured during spatial learning. Here, using intracellular recording, we monitored inputs and plasticity-inducing complex spikes (CSs) in CA1 neurons while mice explored novel and familiar virtual environments. Inputs driving place field spiking increased in amplitude – often suddenly – during novel environment exploration. However, these increases were not sustained in familiar environments. Rather, the spatial tuning of inputs became increasingly similar across repeated traversals of the environment with experience – both within fields and throughout the whole environment. In novel environments, CSs were not necessary for place field formation. Our findings support a model in which initial inhomogeneities in inputs are amplified to produce robust place field activity, then plasticity refines this representation into one with less strongly modulated, but more stable, inputs for long-term storage.

DOI:http://dx.doi.org/10.7554/eLife.23040.001

Dysfunctional long term habituation to exogeneous tinnitus-matched sounds in patients with high tinnitus distress

During the last years, the demand of accurate diagnostic tools for individualized tinnitus treatment gradually increased. Today several different psychometric instruments for the estimation of the patients degree of decompensation with clinical relevance have emerged. All of these tools are questionnaires for a subjective self-assessment and have deficits in comparability due to severe differences in their factor structure in the anamnesis. Those questionnaires thus they are only of limited value in the design of an individualized therapeutic approach. Objective diagnostic tools for the categorization of the patients' distress level are lacking in clinical routine. Scientific approaches yet demonstrated the feasibility of individual distress assessment by objective markers in the EEG. In this article we present the preliminary results of our study of a use of habituation correlates as objective indicator for the decompensation degree in high-distress tinnitus patients.

Failing as doorman and disc jockey at the same time: Amygdalar dysfunction in Parkinson's disease

In Braak's model of ascending degeneration in Parkinson's disease (PD), involvement of the amygdala occurs simultaneously with substantia nigra degeneration. However, the clinical manifestations of amygdalar involvement in PD have not been fully delineated. Considered a multitask manager, the amygdala is a densely connected "hub," coordinating and integrating tasks ranging from prompt, multisensorial emotion recognition to adequate emotional responses and emotional tuning of memories. Although phylogenetically predisposed to handle fear, the amygdala handles both aversive and positive emotional inputs. In PD, neuropathological and in vivo studies suggest primarily amygdalar hypofunction. However, as dopamine acts as an inverted U-shaped amygdalar modulator, medication-induced hyperactivity of the amygdala can occur. We propose that amygdalar (network) dysfunction contributes to reduced recognition of negative emotional face expressions, impaired theory of mind, reactive hypomimia, and impaired decision making. Similarly, impulse control disorders in predisposed individuals, hallucinations, anxiety, and panic attacks may be related to amygdalar dysfunction. When available, we discuss amygdala-independent trigger mechanisms of these symptoms. Although dopaminergic agents have mostly an activation effect on amygdalar function, adaptive and compensatory network changes may occur as well, but these have not been sufficiently explored. In conclusion, our model of amygdalar involvement brings together several elements of Parkinson's disease phenomenology heretofore left unexplained and provides a framework for testable hypotheses in patients during life and in autopsy analyses.

Impaired spatial working memory after anterior thalamic lesions: recovery with cerebrolysin and enrichment

Lesions to the anterior thalamic nuclei (ATN) in rats produce robust spatial memory deficits that reflect their influence as part of an extended hippocampal system. Recovery of spatial working memory after ATN lesions was examined using a 30-day administration of the neurotrophin cerebrolysin and/or an enriched housing environment. As expected, ATN lesions in standard-housed rats given saline produced severely impaired reinforced spatial alternation when compared to standard-housed rats with sham lesions. Both cerebrolysin and enrichment substantially improved this working memory deficit, including accuracy on trials that required attention to distal cues for successful performance. The combination of cerebrolysin and enrichment was more effective than either treatment alone when the delay between successive runs in a trial was increased to 40 s. Compared to the intact rats, ATN lesions in standard-housed groups produced substantial reduction in c-Fos expression in the retrosplenial cortex, which remained low after cerebrolysin and enrichment treatments. Evidence that multiple treatment strategies restore some memory functions in the current lesion model reinforces the prospect for treatments in human diencephalic amnesia.

Patterns of cortical thickness associated with impulse control disorders in Parkinson's disease

Previous functional neuroimaging studies in Parkinson's disease (PD) patients with impulse control disorders (ICDs) demonstrated dysfunction of the reward network, although the extent of anatomical changes is unclear. The aim of this study was to measure brain cortical thickness and subcortical volumes, and to assess their relationship with presence and severity of symptoms, in PD patients with and without ICDs. We studied 110 PD patients (N=58 with ICDs) and 33 healthy controls (all negative for ICDs) who underwent an extensive neurological, neuropsychological, and behavioral assessment as well as structural 1.5 Tesla magnetic resonance imaging (MRI). Between-group differences in brain cortical thickness and subcortical volumes, assessed with the FreeSurfer 5.1 tool, were analyzed. In patients with ICDs, we found significant cortical thinning in fronto-striatal circuitry, specifically in the right superior orbitofrontal, left rostral middle frontal, bilateral caudal middle frontal region, and corpus callosum, as well as volume reduction in the right accumbens and increase in the left amygdala. Finally, we observed a positive association relationship between severity of impulsive symptoms and left rostral middle frontal, inferior parietal, and supramarginal areas. These results support the involvement of both reward and response inhibition networks in PD patients with ICDs. Moreover, their severity is associated with alterations in brain regions linked with reward and top-down control networks. Increased understanding of the mechanisms underlying impulsive and compulsive behaviors might help improve therapeutic strategies for these important disorders.

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.

Neonatal alcohol exposure and the hippocampus in developing male rats: effects on behaviorally induced CA1 c-Fos expression, CA1 pyramidal cell number, and contextual fear conditioning

Rats exposed to a high binge-like dose of alcohol over postnatal days (PD) 4-9 show reductions in CA1 pyramidal cells and impairments on behavioral tasks that depend on the hippocampus. We first examined hippocampal c-Fos expression as a marker of neuronal activity in normally developing rats following different phases of the context preexposure facilitation effect (CPFE) paradigm (Experiment 1). During the CPFE, preexposure to the training context facilitates contextual conditioning to an immediate shock given on a subsequent occasion. We then examined the relationship between CPFE impairment, hippocampal cell loss, and c-Fos expression in rats exposed to alcohol over PD 4-9 (Experiment 2). Normally developing (Experiment 1), sham-intubated control (SI), and PD 4-9 alcohol-exposed (4.00 g and 5.25 g/kg/d; Experiment 2) juvenile male rats were trained on the CPFE. The CPFE occurs over three phases separated by 24 h. Starting on PD 31, rats were preexposed to Context A or Context B for 5 min. After 24 h, all rats received an immediate 1.5-mA foot shock in Context A. Finally, rats were tested for contextual conditioning in Context A on PD 33. Normally developing and SI rats preexposed to Context A showed enhanced contextual fear compared with those preexposed to Context B (Experiment 1) or alcohol-exposed rats preexposed to Context A (Experiment 2). Rats were sacrificed 2 h following different phases of the CPFE and processed for c-Fos immunohistochemistry (Experiments 1 and 2) and CA1 pyramidal cell quantification (Experiment 2). In Experiment 1, c-Fos positive (c-Fos+) cells in the dentate gyrus (DG) were consistently high among rats preexposed to Context A (Pre), Context B (No Pre), or sacrificed directly from their home cage (Home) and did not differ across CPFE phases. CA3 and CA1 c-Fos+ cells were highest during preexposure and decreased across training phases, with Group No Pre showing greater numbers of c-Fos+ cells during training than Group Pre and Controls. In Experiment 2, SI rats had greater numbers of CA1 c-Fos+ cells compared with alcohol-exposed rats, differing significantly from rats exposed to the high alcohol dose (5.25 g) over PD 4-9. Experiment 2 also revealed a linear decline in CA1 pyramidal cells across treatment groups, again with rats from the high-alcohol dose group showing significantly fewer CA1 pyramidal cells compared with SI. Our results reveal that context novelty may be a significant contributor to differential hippocampal c-Fos expression following different phases of the CPFE. In addition, lower levels of c-Fos+ cells in alcohol-exposed rats following preexposure may be related to general reductions in the number of CA1 pyramidal cells in these rats. The significant CPFE impairments in rats exposed to the lower alcohol dose (4.00 g), who show a 15% reduction in CA1 pyramidal cells compared with SI rats, highlight the sensitivity of the CPFE to hippocampal insult.

Neurofunctional model of large-scale correlates of selective attention governed by stimulus-novelty

Multiple studies demonstrate the influence of the limbic system on the processing of sensory events and attentional guidance. But the mechanisms involved therein are yet not entirely clear. The close connection of handling incoming sensory information and memory retrieval, like in the case of habituation towards insignificant stimuli, suggests a crucial impact of the hippocampus on the direction of attention. In this paper we thus present a neurofunctional forward model of a hippocampal comparator function based on the theory of theta-regulated attention. Subsequently we integrated this comparator model into a multiscale framework for the simulation of evoked responses. The results of our simulations were compared to experimental data on electroencephalographic (EEG) correlates of habituation towards familiar stimuli using time-scale analysis. In consequence we are able to present additional evidence for limbic influences on the direction of attention driven by stimulus novelty and a systems neuroscience framework for the statements given in the theta-regulated attention hypothesis.

Electrical synapses control hippocampal contributions to fear learning and memory

The role of electrical synapses in synchronizing neuronal assemblies in the adult mammalian brain is well documented. However, their role in learning and memory processes remains unclear. By combining Pavlovian fear conditioning, activity-dependent immediate early gene expression, and in vivo electrophysiology, we discovered that blocking neuronal gap junctions within the dorsal hippocampus impaired context-dependent fear learning, memory, and extinction. Theta rhythms in freely moving rats were also disrupted. Our results show that gap junction-mediated neuronal transmission is a prominent feature underlying emotional memories.

Excessive novelty-induced c-Fos expression and altered neurogenesis in the hippocampus of GluA1 knockout mice

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA1 subunit-deficient (GluA1-/-) mice display novelty-induced hyperactivity, cognitive and social defects and may model psychiatric disorders, such as schizophrenia and depression/mania. We used c-Fos expression in GluA1-/- mice to identify brain regions responsible for novelty-induced hyperlocomotion. Exposure to a novel cage for 2 h significantly increased c-Fos expression in many brain regions in both wild-type and knockout mice. Interestingly, the clearest genotype effect was observed in the hippocampus and its main input region, the entorhinal cortex, where the novelty-induced c-Fos expression was more strongly enhanced in GluA1-/- mice. Their novelty-induced hyperlocomotion partly depended on the activity of AMPA receptors, as it was diminished by the AMPA receptor antagonist 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulphonamide (NBQX) and unaffected by the AMPA receptor potentiator 2,3-dihydro-1,4-benzodioxin-6-yl-1-piperidinylmethanone (CX546). The hyperlocomotion of GluA1-/- mice was normalised to the level of wild-type mice within 5-6 h, after which their locomotion followed normal circadian rhythm and was not affected by acute or chronic treatments with the selective serotonin reuptake inhibitor escitalopram. We propose that hippocampal dysfunction, as evidenced by the excessive c-Fos response to novelty, is the major contributor to novelty-induced hyperlocomotion in GluA1-/- mice. Hippocampal dysfunction was also indicated by changes in proliferation and survival of adult-born dentate gyrus cells in the knockout mice. These results suggest focusing on the functions of hippocampal formation, such as novelty detection, when using the GluA1-/- mouse line as a model for neuropsychiatric and cognitive disorders.

Molecular specificity of multiple hippocampal processes governing fear extinction

Over many years, fear extinction has been conceptualized as one dominant process, new inhibitory learning, which serves to dampen previously acquired fear. Here we present an alternative view, that brain region-specific processing of representations, expectations and emotional attributes of the fear-provoking event, recruits unique mechanisms that interdependently contribute to the conditioning and extinction of fear. The co-occurrence of these mechanisms within the fear circuit can thus be tracked and differentiated at a molecular and cellular level. Among others, the transcriptional regulators cFos, cAMP-dependent response element binding protein (CREB), Zif268, and extracellular signal-regulated kinases (Erk) stand out as hippocampal nuclear markers signaling novelty, arousal, retrieval, and prediction error, respectively. Consistent with evidence from human studies, these findings indicate that, beyond inhibitory learning, fear extinction requires modification of the emotional attributes and expectations that define the threatening context. Given the likely dysregulation of one or more of these processes in anxiety disorders, a key research challenge for the future is the identification and enhancement of individual extinction mechanisms to target the specific components of fear. Environmental stimuli lacking affective properties (conditioned stimuli, CS) rapidly become threatening if presented with stressful events (unconditioned stimuli, US). Consequently, based on a CS-US association, the presentation of the CS triggers species-specific fear responses until the US consistently stops occurring. At that point, new learning takes place and the fear response declines, a phenomenon termed extinction. The view that extinction occurs because a new, inhibitory CS-noUS association gains control over behavior, has remained dominant in the field. The implications of impaired fear regulation in the development of anxiety disorders have stimulated intense research in this area. Rodent studies identified the circuits involved in the conditioning and extinction of fear of salient cues, generating data that were confirmed in humans with brain imaging approaches. Nevertheless, research with experimental animals has not fully taken advantage of human data in order to better interpret extinction mechanisms in the framework of learning, expectation and emotion governing fear-motivated behavior. The present article aims to summarize recent molecular evidence on fear extinction, focusing on hippocampal mechanisms and experimental models of contextual fear, and compare the results with other relevant fear paradigms and human imaging studies. Instead of conceptualizing extinction learning as one process, such as CS-noUS association or inhibitory learning, we propose that fear extinction reflects the behavioral output of several region-specific learning processes that modify different components of the conditioning memory. The significance of these findings is discussed in the framework of fear regulation and anxiety disorders.

Assessment of aversive stimuli dependent attentional binding by the N170 VEP component

For social species nonverbal communication by assessment of emotion expression is crucial for building up and maintaining social structures. In humans, body language not only includes gestures but also a variety of facial expressions. Negative associated facial expressions, e.g. disgust, fear, anger call for a higher attentional binding due their evolutionary background, denoting directly personal dangers for the receptive individual. In a number of psychiatric disorders such as schizophrenia or autism spectrum diseases, the assessment of emotions in faces is disturbed, leading to even more pronounced social cuts. In this article we present a new methodology for monitoring the attentional binding to emotion-tinged stimuli in a face recognition task. We were able to demonstrate a significant difference in habituation behavior to neutral and negative associated faces respectively. In future, this methodology might provide a fast and reliable scheme for the detection of psychiatric disorders comprising dysfunction of limbic structures.

Modeling limbic influences on habituation deficits in chronic tinnitus aurium

About 93% of healthy subjects suffer from tinnituslike symptoms when deprived of auditory stimuli, e.g., in a sound-proof chamber. This suggests an underlying physiological mechanism causing auditory sensations during absence of an external sound source. Grossberg suggested a mechanism by which hallucinations arise from mechanisms of learning, attention and volition. According to this mechanism notch-like hearing deficits are sufficient for experiencing auditory hallucinations, while their chronification is attributed to reorganization processes. In tinnitus sufferers the auditory sensation is accompanied by the inability to habituate to this endogenous sound. This disability might originate from a coactivation of brain areas that are only indirectly involved in cognitive processing such as areas belonging to the limbic system. Moreover subjective loudness of the tinnitus sensation is likely to depend on the amount of selective attention assigned to the tinnitus stream. Here we propose a functional model of pure-tone tinnitus in which exogenous and endogenous input into processing modules is represented as streams. We model the selection of the tinnitus stream at the subthalamic level according to its weighting. Then we propose a mechanism for the inability to habituate to this stream due to limbic coactivation and amplification by mechanisms of attentional guidance, and by the influence corticofugal projections on lower auditory processing stages. The model is able to replicate the phase stability of auditory evoked potentials as seen in tinnitus sufferers and controls.

Categories of Novelty and States of Uncertainty

The concept of novelty has acquired a large number of diverse referents over the past quarter-century as a result of new methods that permit measurement of a variety of biological and behavioral reactions to novel incentives in both humans and animals. As a result, the term has acquired varied meanings. This analysis of novelty makes four claims. First, the specific state of uncertainty that a novel event creates depends on its origin. Second, unexpected events that alter the immediate stimulus surround (called stimulus novelty) should be distinguished from those that are inconsistent with an agent's long term knowledge (called conceptual novelty). Third, the critical features that render an event novel can vary with the agent's intention to classify or to act on an object and the balance between these two frames changes with development. Finally, the state of uncertainty created when an agent must choose one response from two or more alternatives differs from the states provoked by stimulus and conceptual novelty.

Corticotropin-releasing factor (CRF) sensitization of ethanol withdrawal-induced anxiety-like behavior is brain site specific and mediated by CRF-1 receptors: relation to stress-induced sensitization

In abstinent alcoholics, stress induces negative affect-a response linked to craving and relapse. In rats, repeated stresses at weekly intervals before 5-day ethanol diet sensitize withdrawal-induced anxiety-like behavior ("anxiety") that is blocked by a corticotrophin-releasing factor 1 (CRF-1)-receptor antagonist. Current experiments were performed to identify brain sites that support CRF involvement in stress sensitization of ethanol withdrawal-induced anxiety-like behavior. First, different doses of CRF microinjected weekly into the central amygdala (CeA) before ethanol exposure produced a dose-related sensitization of anxiety during ethanol withdrawal. Subsequently, CRF microinjection into the basolateral amygdala, dorsal raphe nucleus (DRN), or dorsal bed nucleus of the stria terminalis (d-BNST) also sensitized ethanol withdrawal-induced anxiety. In contrast, sensitization of ethanol withdrawal-induced anxiety was not observed after weekly CRF administration into the ventral-BNST, CA1-hippocampal region, or hypothalamic-paraventricular nucleus. Then, experiments documented the CRF receptor subtype responsible for CRF and stress sensitization of withdrawal-induced anxiety. Systemic administration of a CRF-1 receptor antagonist before CRF microinjection into the CeA, DRN, or d-BNST prevented CRF-induced sensitization of anxiety during ethanol withdrawal. Furthermore, repeated microinjections of urocortin-3, a CRF-2 receptor agonist, into the CRF-positive sites did not sensitize anxiety after withdrawal from ethanol. Finally, microinjection of a CRF-1 receptor antagonist into the CeA, DRN, or d-BNST before stress blocked sensitization of anxiety-like behavior induced by the repeated stress/ethanol withdrawal protocol. These results indicate that CRF released by stress acts on CRF-1 receptors within specific brain regions to produce a cumulative adaptation that sensitizes anxiety-like behavior during withdrawal from chronic ethanol exposure.

Connectivity-based segregation of the human striatum predicts personality characteristics

We found that personality characteristics are linked to dissociable connectivity streams in the human brain. Whereas fiber tracts between a subcortical network, including the hippocampus and amygdala, and the ventral striatum predicted individual differences in novelty seeking, tracts between prefrontal cortex and the striatum predicted individual differences in reward dependence. These findings suggest that the strength of limbic-striatal connectivity may, in part, underlie human personality traits.

Parallel memory processing by the CA1 region of the dorsal hippocampus and the basolateral amygdala

There is abundant literature on the role of the basolateral amygdala (BLA) and the CA1 region of the hippocampus in memory formation of inhibitory avoidance (IA) and other behaviorally arousing tasks. Here, we investigate molecular correlates of IA consolidation in the two structures and their relation to NMDA receptors (NMDArs) and beta-adrenergic receptors (beta-ADrs). The separate posttraining administration of antagonists of NMDAr and beta-ADr to BLA and CA1 is amnesic. IA training is followed by an increase of the phosphorylation of calcium and calmodulin-dependent protein kinase II (CaMKII) and ERK2 in CA1 but only an increase of the phosphorylation of ERK2 in BLA. The changes are blocked by NMDAr antagonists but not beta-ADr antagonists in CA1, and they are blocked by beta-ADr but not NMDAr antagonists in BLA. In addition, the changes are accompanied by increased phosphorylation of tyrosine hydroxylase in BLA but not in CA1, suggesting that beta-AD modulation results from local catecholamine synthesis in the former but not in the latter structure. NMDAr blockers in CA1 do not alter the learning-induced neurochemical changes in BLA, and beta-ADr blockade in BLA does not hinder those in CA1. When put together with other data from the literature, the present findings suggest that CA1 and BLA play a role in consolidation, but they operate to an extent in parallel, suggesting that each is probably involved with different aspects of the task studied.