The amygdala and prioritization of declarative memories

Differential effects of emotional valence on mnemonic performance with greater hippocampal maturity

The hippocampal formation (HF) facilitates declarative memory, with subfields providing unique contributions to memory performance. Maturational differences across subfields facilitate a shift toward increased memory specificity, with peripuberty sitting at the inflection point. Peripuberty is also a sensitive period in the development of anxiety disorders. We believe HF development during puberty is critical to negative overgeneralization, a common feature of anxiety disorders. To investigate this claim, we examined the relationship between mnemonic generalization and a cross-sectional pubertal maturity index (PMI) derived from partial least squares correlation (PLSC) analyses of subfield volumes and structural connectivity from T1-weighted and diffusion-weighted scans, respectively. Participants aged 9-14 yr, from clinical and community sources, performed a recognition task with emotionally valent (positive, negative, and neutral) images. HF volumetric PMI was positively associated with generalization for negative images. Hippocampal-medial prefrontal cortex connectivity PMI evidenced a behavioral relationship similar to that of the HF volumetric approach. These findings reflect a novel developmentally related balance between generalization behavior supported by the hippocampus and its connections with other regions, with maturational differences in this balance potentially contributing to negative overgeneralization during peripuberty.

Sleep fragmentation affects glymphatic system through the different expression of AQP4 in wild type and 5xFAD mouse models

Alzheimer's disease (AD) is characterized by genetic and multifactorial risk factors. Many studies correlate AD to sleep disorders. In this study, we performed and validated a mouse model of AD and sleep fragmentation, which properly mimics a real condition of intermittent awakening. We noticed that sleep fragmentation induces a general acceleration of AD progression in 5xFAD mice, while in wild type mice it affects cognitive behaviors in particular learning and memory. Both these events may be correlated to aquaporin-4 (AQP4) modulation, a crucial player of the glymphatic system activity. In particular, sleep fragmentation differentially affects aquaporin-4 channel (AQP4) expression according to the stage of the disease, with an up-regulation in younger animals, while such change cannot be detected in older ones. Moreover, in wild type mice sleep fragmentation affects cognitive behaviors, in particular learning and memory, by compromising the glymphatic system through the decrease of AQP4. Nevertheless, an in-depth study is needed to better understand the mechanism by which AQP4 is modulated and whether it could be considered a risk factor for the disease development in wild type mice. If our hypotheses are going to be confirmed, AQP4 modulation may represent the convergence point between AD and sleep disorder pathogenic mechanisms.

Neuronal activity in the human amygdala and hippocampus enhances emotional memory encoding

Emotional events comprise our strongest and most valuable memories. Here we examined how the brain prioritizes emotional information for storage using direct brain recording and deep brain stimulation. First, 148 participants undergoing intracranial electroencephalographic (iEEG) recording performed an episodic memory task. Participants were most successful at remembering emotionally arousing stimuli. High-frequency activity (HFA), a correlate of neuronal spiking activity, increased in both the hippocampus and the amygdala when participants successfully encoded emotional stimuli. Next, in a subset of participants (N = 19), we show that applying high-frequency electrical stimulation to the hippocampus selectively diminished memory for emotional stimuli and specifically decreased HFA. Finally, we show that individuals with depression (N = 19) also exhibit diminished emotion-mediated memory and HFA. By demonstrating how direct stimulation and symptoms of depression unlink HFA, emotion and memory, we show the causal and translational potential of neural activity in the amygdalohippocampal circuit for prioritizing emotionally arousing memories.

Independent effects of emotional arousal and reward anticipation on episodic memory formation

Events that elicit emotional arousal or are associated with reward are more likely remembered. Emotional arousal activates the amygdala and the central noradrenergic system, whereas reward anticipation results in an activity in the mesocorticolimbic dopaminergic system. The activation of both pathways enhances memory formation in the hippocampus where their effects are based on similar neural substrates, e.g. tagging of active hippocampal synapses. Moreover, emotional arousal and reward anticipation both enhance attention, which can also affect memory formation. In addition, both neuromodulators interact on the cellular level. Therefore, we tested in the current functional magnetic resonance imaging study whether simultaneously occurring emotional arousal and reward anticipation might have interacting effects on memory formation. We did not find evidence for such an interaction, neither on the behavioral nor on the neural level. Our results further suggest that reward anticipation enhances memory formation rather by an increase in anticipation-related arousal-reflected in activity in the dorsal anterior cingulate cortex-and not dopaminergic midbrain activity. Accompanying behavioral experiments indicated that the effect of reward anticipation on memory is (i) caused at least to some extent by anticipating the speeded response to obtain the reward and not by the valance of the outcome and (ii) can be observed already immediately after encoding, i.e. before consolidation.

Affective Episodic Memory System for Virtual Creatures: The First Step of Emotion-Oriented Memory

Episodic memory and emotions are considered essential functions in human cognition. Both allow us to acquire new knowledge from the environment, ranging from the objects around us to how we feel towards them. These qualities make them crucial functions for systems trying to create human-like behaviour. In the field of cognitive architectures (CAs), there are multiple studies covering memory and emotions. However, most of them treat these subjects in an isolated manner, considering emotions only as a reward signal unrelated to a retrieved experience. To address this lack of direct interaction, we propose a computational model that covers the common processes that are related to memory and emotions. Specifically, this proposal focuses on affective evaluations of episodic memories. Neurosciences and psychology are the bases of this model. That is, the model's components and the processes that they carry out on the information they receive are designed based on evidence from these cognitive sciences. The proposed model is a part of Cuáyóllótl, a cognitive architecture for cybernetic entities such as virtual creatures and robots. Case studies validate our proposal. They show the relevance of the integration of emotions and memory in a virtual creature. The virtual creature endowed with our emotional episodic model improves its learning and modifies its behaviour according to planning and decision-making processes.

Prioritization of social information by the basolateral amygdala in rats

The amygdala is a collection of nuclei that support adaptive social behavior and are implicated in disorders such as autism. The basolateral complex of the amygdala (BLA), a main subdivision of the amygdala, influences fear responses, motivated behavior, and memory of emotional events via its communication with other amygdalar nuclei and with other brain regions such as the prefrontal cortex, striatum, and hippocampus. The specific role of the BLA in responses to social stimuli is less clear. The present study of female rats investigated the role of the BLA in responding to socially-relevant information by asking how inactivation of the BLA with bilateral infusions of the GABA receptor agonist muscimol would affect spontaneous exploration of wood blocks scented either with conspecific male or female urine or with nonsocial odorants. Conspecific urine samples were used because urine conveys information about sex, health, social status, and reproductive state in rodents. The results revealed that BLA inactivation reduced female rats' spontaneous preference for social odors over nonsocial odors, specifically for female urine. However, BLA inactivation did not generally impair rats' ability to distinguish two odors from the same category (e.g., urine odors from two different male rats). The results indicate that the BLA is important for responding to salience of social stimuli but not for discriminating between different individuals, a result that has important implications for amygdalar modulation of downstream attention, motivation, and memory processes for social stimuli.

Cell Adhesion Factors in the Orbitofrontal Cortex Control Cue-Induced Reinstatement of Cocaine Seeking and Amygdala-Dependent Goal Seeking

Repeated cocaine exposure causes dendritic spine loss in the orbitofrontal cortex, which might contribute to poor orbitofrontal cortical function following drug exposure. One challenge, however, has been verifying links between neuronal structural plasticity and behavior, if any. Here we report that cocaine self-administration triggers the loss of dendritic spines on excitatory neurons in the orbitofrontal cortex of male and female mice (as has been reported in rats). To understand functional consequences, we locally ablated neuronal β1-integrins, cell adhesion receptors that adhere cells to the extracellular matrix and thus support dendritic spine stability. Degradation of β1-integrin tone: (1) caused dendritic spine loss, (2) exaggerated cocaine-seeking responses in a cue-induced reinstatement test, and (3) impaired the ability of mice to integrate new learning into familiar routines, a key function of the orbitofrontal cortex. Stimulating Abl-related gene kinase, overexpressing Proline-rich tyrosine kinase, and inhibiting Rho-associated coiled-coil containing kinase corrected response strategies, uncovering a β1-integrin-mediated signaling axis that controls orbitofrontal cortical function. Finally, use of a combinatorial gene silencing/chemogenetic strategy revealed that β1-integrins support the ability of mice to integrate new information into established behaviors by sustaining orbitofrontal cortical connections with the basolateral amygdala.SIGNIFICANCE STATEMENT Cocaine degenerates dendritic spines in the orbitofrontal cortex, a region of the brain involved in interlacing new information into established behaviors. One challenge has been verifying links between cellular structural stability and behavior, if any. In this second of two related investigations, we study integrin family receptors, which adhere cells to the extracellular matrix and thereby stabilize dendritic spines (see also DePoy et al., 2019). We reveal that β1-integrins in the orbitofrontal cortex control food- and cocaine-seeking behaviors. For instance, β1-integrin loss amplifies cocaine-seeking behavior and impairs the ability of mice to integrate new learning into familiar routines. We identify likely intracellular signaling partners by which β1-integrins support orbitofrontal cortical function and connectivity with the basolateral amygdala.

Optogenetic stimulation of the basolateral amygdala accelerates acquisition of object-context associations

The basolateral complex of the amygdala (BLA) is capable of modulating memory and is thought to do so via projections to regions such as the hippocampus. The present study used optogenetic stimulation of glutamatergic projection neurons in the BLA as rats learned object-context associations during a well-studied hippocampus-dependent memory task. Relative to a control condition, optogenetic BLA stimulation resulted in the accelerated acquisition of when stimulation was delivered following correct choices but not when it was delivered during the intertrial interval. These results extend prior examples of amygdala-mediated memory enhancement to a canonical example of hippocampus-dependent memory and provide an opportunity for future dissection of amygdalar modulation of object-context associative memory. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Test-retest reliability of the emotional enhancement of memory

Emotionally arousing stimuli are usually better remembered than neutral ones. This effect can be observed immediately after encoding and becomes more robust after a period of consolidation. The magnitude of this effect in an individual has been treated in various research contexts implicitly as reliable and temporally stable. However, we recently observed in 69 participants that an individual's memory advantage for negative over neutral stimuli, whether immediate or delayed, was very weakly correlated with the advantage measured after 3.5 years, albeit with slightly different memory paradigms. In the current study, we tested whether the test-retest reliability of these emotional memory effects might be larger if the temporal lapse between tests was shorter (10 weeks) and more similar memory tests were used. We observed that the better memory for emotional stimuli is highly replicable on the group level. However, the retest reliability on the individual level was very low. We replicated these findings by re-analysing data from a previous study where female participants took emotional memory tests at two different points of their menstrual cycle. We conclude, therefore, that the individual emotional enhancement of memory is not stable or that it cannot be measured reliably with the standard emotional memory paradigm.

Optogenetic Stimulation of the Basolateral Amygdala Increased Theta-Modulated Gamma Oscillations in the Hippocampus

The amygdala can modulate declarative memory. For example, previous research in rats and humans showed that brief electrical stimulation to the basolateral complex of the amygdala (BLA) prioritized specific objects to be consolidated into long term memory in the absence of emotional stimuli and without awareness of stimulation. The capacity of the BLA to influence memory depends on its substantial projections to many other brain regions, including the hippocampus. Nevertheless, how activation of the BLA influences ongoing neuronal activity in other regions is poorly understood. The current study used optogenetic stimulation of putative glutamatergic neurons in the BLA of freely exploring rats to determine whether brief activation of the BLA could increase in the hippocampus gamma oscillations for which the amplitude was modulated by the phase of theta oscillations, an oscillatory state previously reported to correlate with good memory. BLA neurons were stimulated in 1-s bouts with pulse frequencies that included the theta range (8 Hz), the gamma range (50 Hz), or a combination of both ranges (eight 50-Hz bursts). Local field potentials were recorded in the BLA and in the pyramidal layer of CA1 in the intermediate hippocampus. A key question was whether BLA stimulation at either theta or gamma frequencies could combine with ongoing hippocampal oscillations to result in theta-modulated gamma or whether BLA stimulation that included both theta and gamma frequencies would be necessary to increase theta–gamma comodulation in the hippocampus. All stimulation conditions elicited robust responses in BLA and CA1, but theta-modulated gamma oscillations increased in CA1 only when BLA stimulation included both theta and gamma frequencies. Longer bouts (5-s) of BLA stimulation resulted in hippocampal activity that evolved away from the initial oscillatory states and toward those characterized more by prominent low-frequency oscillations. The current results indicated that one mechanism by which the amygdala might influence declarative memory is by eliciting neuronal oscillatory states in the hippocampus that benefit memory.

Shared Mechanisms May Support Mnemonic Benefits from Self-Referencing and Emotion

The literatures on episodic memory for self-referential and emotional information have proceeded relatively independently, and most studies examining the effects of age on these memory processes have been interpreted within domain-specific frameworks. However, there is increasing evidence for shared mechanisms that contribute to episodic memory benefits in these two domains. We review this evidence and propose a model that incorporates overlapping as well as domain-specific contributions to episodic memory encoding of self-referential and emotional material. We discuss the implications for understanding the relatively intact memory of older adults for these classes of stimuli, and conclude with suggestions for future research to test key tenets and extensions of this shared-process model.

Dissociable contributions of the amygdala to the immediate and delayed effects of emotional arousal on memory

Emotional arousal enhances memory encoding and consolidation leading to better immediate and delayed memory. Although the central noradrenergic system and the amygdala play critical roles in both effects of emotional arousal, we have recently shown that these effects are at least partly independent of each other, suggesting distinct underlying neural mechanisms. Here we aim to dissociate the neural substrates of both effects in 70 female participants using an emotional memory paradigm to investigate how neural activity, as measured by fMRI, and a polymorphism in the α_2B-noradrenoceptor vary for these effects. To also test whether the immediate and delayed effects of emotional arousal on memory are stable traits, we invited back participants who were a part of a large-scale behavioral memory study ∼3.5 yr ago. We replicated the low correlation of the immediate and delayed emotional enhancement of memory across participants (r = 0.16) and observed, moreover, that only the delayed effect was, to some degree, stable over time (r = 0.23). Bilateral amygdala activity, as well as its coupling with the visual cortex and the fusiform gyrus, was related to the preferential encoding of emotional stimuli, which is consistent with affect-biased attention. Moreover, the adrenoceptor genotype modulated the bilateral amygdala activity associated with this effect. The left amygdala and its coupling with the hippocampus was specifically associated with the more efficient consolidation of emotional stimuli, which is consistent with amygdalar modulation of hippocampal consolidation.

Direct electrical stimulation of the amygdala enhances declarative memory in humans

Emotional events are often remembered better than neutral events, a benefit that many studies have hypothesized to depend on the amygdala's interactions with memory systems. These studies have indicated that the amygdala can modulate memory-consolidation processes in other brain regions such as the hippocampus and perirhinal cortex. Indeed, rodent studies have demonstrated that direct activation of the amygdala can enhance memory consolidation even during nonemotional events. However, the premise that the amygdala causally enhances declarative memory has not been directly tested in humans. Here we tested whether brief electrical stimulation to the amygdala could enhance declarative memory for specific images of neutral objects without eliciting a subjective emotional response. Fourteen epilepsy patients undergoing monitoring of seizures via intracranial depth electrodes viewed a series of neutral object images, half of which were immediately followed by brief, low-amplitude electrical stimulation to the amygdala. Amygdala stimulation elicited no subjective emotional response but led to reliably improved memory compared with control images when patients were given a recognition-memory test the next day. Neuronal oscillations in the amygdala, hippocampus, and perirhinal cortex during this next-day memory test indicated that a neural correlate of the memory enhancement was increased theta and gamma oscillatory interactions between these regions, consistent with the idea that the amygdala prioritizes consolidation by engaging other memory regions. These results show that the amygdala can initiate endogenous memory prioritization processes in the absence of emotional input, addressing a fundamental question and opening a path to future therapies.

Effects of lesions in different nuclei of the amygdala on conditioned taste aversion

Conditioned taste aversion (CTA) is an adaptive learning that depends on brain mechanisms not completely identified. The amygdala is one of the structures that make up these mechanisms, but the involvement of its nuclei in the acquisition of CTA is unclear. Lesion studies suggest that the basolateral complex of the amygdala, including the basolateral and lateral amygdala, could be involved in CTA. The central amygdala has also been considered as an important nucleus for the acquisition of CTA in some studies. However, to the best of our knowledge, the effect of lesions of the basolateral complex of the amygdala on the acquisition of CTA has not been directly compared with the effect of lesions of the central and medial nuclei of the amygdala. The aim of this study is to compare the effect of lesions of different nuclei of the amygdala (the central and medial amygdala and the basolateral complex) on the acquisition of taste aversion in male Wistar rats. The results indicate that lesions of the basolateral complex of the amygdala reduce the magnitude of the CTA when compared with lesions of the other nuclei and with animals without lesions. These findings suggest that the involvement of the amygdala in the acquisition of CTA seems to depend particularly on the integrity of the basolateral complex of the amygdala.

PTSD in Court II: Risk factors, endophenotypes, and biological underpinnings in PTSD

The second article in the series of three for the journal on "PTSD in Court" especially concerns the biological bases that have been found to be associated with PTSD (posttraumatic stress disorder). The cohering concepts in this section relate to risk factors; candidate genes; polygenetics; "gene×environment" interactions; epigenetics; endophenotypes; biomarkers; and connective networks both structurally and functionally (in terms of intrinsic connectivity networks, ICNs, including the DMN, SN, and CEN; that is, default mode, salience, and central executive networks, respectively). Risk factors related to PTSD include pre-event, event- and post-event ones. Some of the genes related to PTSD include: FKBP5, 5-HTTLPR, and COMT (which are, respectively, FK506-binding protein 5 gene, serotonin-transporter linked polymorphic region, catechol-O-methyl-transferase). These genetic findings give an estimate of 30% for the genetic influence on PTSD. The typical brain regions involved in PTSD include the amygdala, hippocampus, and prefrontal cortex, along with the insula. Causal models of behavior are multifactorial and biopsychosocial, and these types of models apply to PTSD, as well. The paper presents a multilevel systems model of psychopathology, including PTSD, which involves three levels - a top-down psychological construct one, a bottom-up symptom connection one, and a middle one involving symptom appraisal. Legally, causality refers to the event at issue needing to meet the bar of being materially contributory to the outcome. Finally, this section of the article reviews empirically-supported therapies for PTSD and the dangers of not receiving treatment for it.