Encoding of fear learning and memory in distributed neuronal circuits

Dynamical prefrontal population coding during defensive behaviours

Coping with threatening situations requires both identifying stimuli that predict danger and selecting adaptive behavioural responses to survive¹. The dorsomedial prefrontal cortex (dmPFC) is a critical structure that is involved in the regulation of threat-related behaviour^2-4. However, it is unclear how threat-predicting stimuli and defensive behaviours are associated within prefrontal networks to successfully drive adaptive responses. Here we used a combination of extracellular recordings, neuronal decoding approaches, pharmacological and optogenetic manipulations to show that, in mice, threat representations and the initiation of avoidance behaviour are dynamically encoded in the overall population activity of dmPFC neurons. Our data indicate that although dmPFC population activity at stimulus onset encodes sustained threat representations driven by the amygdala, it does not predict action outcome. By contrast, transient dmPFC population activity before the initiation of action reliably predicts avoided from non-avoided trials. Accordingly, optogenetic inhibition of prefrontal activity constrained the selection of adaptive defensive responses in a time-dependent manner. These results reveal that the adaptive selection of defensive responses relies on a dynamic process of information linking threats with defensive actions, unfolding within prefrontal networks.

The parabrachial-to-amygdala pathway provides aversive information to induce avoidance behavior in mice

The neuronal circuitry for pain signals has been intensively studied for decades. The external lateral parabrachial nucleus (PB) was shown to play a crucial role in nociceptive information processing. Previous work, including ours, has demonstrated that stimulating the neuronal pathway from the PB to the central region of the amygdala (CeA) can substitute for an actual pain signal to drive an associative form of threat/fear memory formation. However, it is still unknown whether activation of the PB-CeA pathway can directly drive avoidance behavior, escape behavior, or only acts as strategic freezing behavior for later memory retrieval. To directly address this issue, we have developed a real-time Y-maze conditioning behavioral paradigm to examine avoidance behavior induced by optogenetic stimulation of the PB-CeA pathway. In this current study, we have demonstrated that the PB-CeA pathway carries aversive information that can directly trigger avoidance behavior and thereby serve as an alarm signal to induce adaptive behaviors for later decision-making.

The lesser evil: Pavlovian-instrumental transfer & aversive motivation

While our understanding of appetitive motivation includes accounts of rich cognitive phenomena, such as choice, sensory-specificity and outcome valuation, the same is not true in aversive processes. A highly sophisticated picture has emerged of Pavlovian fear conditioning and extinction, but progress in aversive motivation has been somewhat limited to these fundamental behaviors. Many differences between appetitive and aversive stimuli permit different kinds of analyses; a widely used procedure in appetitive studies that can expand the scope of aversive motivation is Pavlovian-instrumental transfer (PIT). Recently, this motivational transfer effect has been used to examine issues pertaining to sensory-specificity and the nature of defensive control in avoidance learning. Given enduring controversies and unresolved criticisms surrounding avoidance research, PIT offers a valuable, well-controlled procedure with which to similarly probe this form of motivation. Furthermore, while avoidance itself can be criticized as artificial, PIT can be an effective model for how skills learned through avoidance can be practically applied to encounters with threatening or fearful stimuli and stress. Despite sensory-related challenges presented by the limited aversive unconditioned stimuli typically used in research, transfer testing can nevertheless provide valuable information on the psychological nature of this historically controversial phenomenon.

Involvement of Cerebellar Neural Circuits in Active Avoidance Conditioning in Zebrafish

When animals repeatedly receive a combination of neutral conditional stimulus (CS) and aversive unconditional stimulus (US), they learn the relationship between CS and US, and show conditioned fear responses after CS. They show passive responses such as freezing or panic movements (classical or Pavlovian fear conditioning), or active behavioral responses to avoid aversive stimuli (active avoidance). Previous studies suggested the roles of the cerebellum in classical fear conditioning but it remains elusive whether the cerebellum is involved in active avoidance conditioning. In this study, we analyzed the roles of cerebellar neural circuits during active avoidance in adult zebrafish. When pairs of CS (light) and US (electric shock) were administered to wild-type zebrafish, about half of them displayed active avoidance. The expression of botulinum toxin, which inhibits the release of neurotransmitters, in cerebellar granule cells (GCs) or Purkinje cells (PCs) did not affect conditioning-independent swimming behaviors, but did inhibit active avoidance conditioning. Nitroreductase (NTR)-mediated ablation of PCs in adult zebrafish also impaired active avoidance. Furthermore, the inhibited transmission of GCs or PCs resulted in reduced fear-conditioned Pavlovian fear responses. Our findings suggest that the zebrafish cerebellum plays an active role in active avoidance conditioning.

Midbrain dopaminergic inputs gate amygdala intercalated cell clusters by distinct and cooperative mechanisms in male mice

Dopaminergic signaling plays an important role in associative learning, including fear and extinction learning. Dopaminergic midbrain neurons encode prediction error-like signals when threats differ from expectations. Within the amygdala, GABAergic intercalated cell (ITC) clusters receive one of the densest dopaminergic projections, but their physiological consequences are incompletely understood. ITCs are important for fear extinction, a function thought to be supported by activation of ventromedial ITCs that inhibit central amygdala fear output. In mice, we reveal two distinct novel mechanisms by which mesencephalic dopaminergic afferents control ITCs. Firstly, they co-release GABA to mediate rapid, direct inhibition. Secondly, dopamine suppresses inhibitory interactions between distinct ITC clusters via presynaptic D1 receptors. Early extinction training augments both GABA co-release onto dorsomedial ITCs and dopamine-mediated suppression of dorso- to ventromedial inhibition between ITC clusters. These findings provide novel insights into dopaminergic mechanisms shaping the activity balance between distinct ITC clusters that could support their opposing roles in fear behavior.

Time-Dependent Recruitment of Prelimbic Prefrontal Circuits for Retrieval of Fear Memory

The long-lasting nature of fear memories is essential for survival, but the neural circuitry for retrieval of these associations changes with the passage of time. We previously reported a time-dependent shift from prefrontal-amygdalar circuits to prefrontal-thalamic circuits for the retrieval of auditory fear conditioning. However, little is known about the time-dependent changes in the originating site, the prefrontal cortex. Here we monitored the responses of prelimbic (PL) prefrontal neurons to conditioned tones at early (2 h) vs. late (4 days) timepoints following training. Using c-Fos, we find that PL neurons projecting to the amygdala are activated early after learning, but not later, whereas PL neurons projecting to the paraventricular thalamus (PVT) show the opposite pattern. Using unit recording, we find that PL neurons in layer V (the origin of projections to amygdala) showed cue-induced excitation at earlier but not later timepoints, whereas PL neurons in Layer VI (the origin of projections to PVT) showed cue-induced inhibition at later, but not earlier, timepoints, along with an increase in spontaneous firing rate. Thus, soon after conditioning, there are conditioned excitatory responses in PL layer V which influence the amygdala. With the passage of time, however, retrieval of fear memories shifts to inhibitory responses in PL layer VI which influence the midline thalamus.

Amygdala Circuit Substrates for Stress Adaptation and Adversity

Brain systems that promote maintenance of homeostasis in the face of stress have significant adaptive value. A growing body of work across species demonstrates a critical role for the amygdala in promoting homeostasis by regulating physiological and behavioral responses to stress. This review focuses on an emerging body of evidence that has begun to delineate the contribution of specific long-range amygdala circuits in mediating the effects of stress. After summarizing the major anatomical features of the amygdala and its connectivity to other limbic structures, we discuss recent findings from rodents showing how stress causes structural and functional remodeling of amygdala neuronal outputs to defined cortical and subcortical target regions. We also consider some of the environmental and genetic factors that have been found to moderate how the amygdala responds to stress and relate the emerging preclinical literature to the current understanding of the pathophysiology and treatment of stress-related neuropsychiatric disorders. Future effort to translate these findings to clinics may help to develop valuable tools for prevention, diagnosis, and treatment of these diseases.

Single cell plasticity and population coding stability in auditory thalamus upon associative learning

Cortical and limbic brain areas are regarded as centres for learning. However, how thalamic sensory relays participate in plasticity upon associative learning, yet support stable long-term sensory coding remains unknown. Using a miniature microscope imaging approach, we monitor the activity of populations of auditory thalamus (medial geniculate body) neurons in freely moving mice upon fear conditioning. We find that single cells exhibit mixed selectivity and heterogeneous plasticity patterns to auditory and aversive stimuli upon learning, which is conserved in amygdala-projecting medial geniculate body neurons. Activity in auditory thalamus to amygdala-projecting neurons stabilizes single cell plasticity in the total medial geniculate body population and is necessary for fear memory consolidation. In contrast to individual cells, population level encoding of auditory stimuli remained stable across days. Our data identifies auditory thalamus as a site for complex neuronal plasticity in fear learning upstream of the amygdala that is in an ideal position to drive plasticity in cortical and limbic brain areas. These findings suggest that medial geniculate body's role goes beyond a sole relay function by balancing experience-dependent, diverse single cell plasticity with consistent ensemble level representations of the sensory environment to support stable auditory perception with minimal affective bias.

BEHAVIORAL AND NEUROBIOLOGICAL MECHANISMS OF PAVLOVIAN AND INSTRUMENTAL EXTINCTION LEARNING

This article reviews the behavioral neuroscience of extinction, the phenomenon in which a behavior that has been acquired through Pavlovian or instrumental (operant) learning decreases in strength when the outcome that reinforced it is removed. Behavioral research indicates that neither Pavlovian nor operant extinction depends substantially on erasure of the original learning but instead depends on new inhibitory learning that is primarily expressed in the context in which it is learned, as exemplified by the renewal effect. Although the nature of the inhibition may differ in Pavlovian and operant extinction, in either case the decline in responding may depend on both generalization decrement and the correction of prediction error. At the neural level, Pavlovian extinction requires a tripartite neural circuit involving the amygdala, prefrontal cortex, and hippocampus. Synaptic plasticity in the amygdala is essential for extinction learning, and prefrontal cortical inhibition of amygdala neurons encoding fear memories is involved in extinction retrieval. Hippocampal-prefrontal circuits mediate fear relapse phenomena, including renewal. Instrumental extinction involves distinct ensembles in corticostriatal, striatopallidal, and striatohypothalamic circuits as well as their thalamic returns for inhibitory (extinction) and excitatory (renewal and other relapse phenomena) control over operant responding. The field has made significant progress in recent decades, although a fully integrated biobehavioral understanding still awaits.

Vortioxetine attenuates the effects of early-life stress on depression-like behaviors and monoamine transporters in female mice

Major depressive disorder is a major psychiatric disorder and a leading cause of disability around the world. Females have about twice as high an incidence of depression as males. However, preclinical animal models of depression have seldom investigated the molecular alterations associated with higher depression risk in females. In this study, adopting the early-life stress (ELS) paradigm of limited bedding and nesting material, we found that ELS induced depression-like behaviors only in adult female mice, as evaluated by sucrose preference and tail suspension tests. We then examined the ELS effects on monoamine neurotransmission (transporters for monoamine reuptake and release) in depression-related brain regions in female mice. We found that ELS resulted in widespread changes of the expression levels of these transporters in four brain regions. Moreover, systemic 21-day treatment with vortioxetine, a novel multimodal antidepressant, successfully reversed depression-like behaviors and normalized some molecular changes, including that of the norepinephrine transporter in the medial prefrontal cortex, vesicular monoamine transporter 2 in nucleus accumbens core, and serotonin transporter in amygdala. Collectively, these results provide evidence for the validity of using the limited bedding and nesting material paradigm to investigate sex differences in depression and demonstrate that the region-specific alterations of monoamine neurotransmission may be associated with depression-like behaviors in female mice. This article is part of the special issue on 'Stress, Addiction and Plasticity'.

The social dilemma: prefrontal control of mammalian sociability

Mammalian social interactions are orchestrated by a wide array of neural circuits. While some aspects of social behaviors are driven by subcortical circuits, and are considered to be highly conserved and hard-wired, others require dynamic and context-dependent modulation that integrates current state, past experience and goal-driven action selection. These cognitive social processes are known to be dependent on the integrity of the prefrontal cortex. However, the circuit mechanisms through which the prefrontal cortex supports complex social functions are still largely unknown, and it is unclear if and how they diverge from prefrontal control of behavior outside of the social domain. Here we review recent studies exploring the role of prefrontal circuits in mammalian social functions, and attempt to synthesize these findings to a holistic view of prefrontal control of sociability.

A review of decreased sound tolerance in autism: Definitions, phenomenology, and potential mechanisms

Atypical behavioral responses to environmental sounds are common in autistic children and adults, with 50-70 % of this population exhibiting decreased sound tolerance (DST) at some point in their lives. This symptom is a source of significant distress and impairment across the lifespan, contributing to anxiety, challenging behaviors, reduced community participation, and school/workplace difficulties. However, relatively little is known about its phenomenology or neurocognitive underpinnings. The present article synthesizes a large body of literature on the phenomenology and pathophysiology of DST-related conditions to generate a comprehensive theoretical account of DST in autism. Notably, we argue against conceptualizing DST as a unified construct, suggesting that it be separated into three phenomenologically distinct conditions: hyperacusis (the perception of everyday sounds as excessively loud or painful), misophonia (an acquired aversive reaction to specific sounds), and phonophobia (a specific phobia of sound), each responsible for a portion of observed DST behaviors. We further elaborate our framework by proposing preliminary neurocognitive models of hyperacusis, misophonia, and phonophobia that incorporate neurophysiologic findings from studies of autism.

Neural Computations of Threat

A host of learning, memory, and decision-making processes form the individual's response to threat and may be disrupted in anxiety and post-trauma psychopathology. Here we review the neural computations of threat, from the first encounter with a dangerous situation, through learning, storing, and updating cues that predict it, to making decisions about the optimal course of action. The overview highlights the interconnected nature of these processes and their reliance on shared neural and computational mechanisms. We propose an integrative approach to the study of threat-related processes, in which specific computations are studied across the various stages of threat experience rather than in isolation. This approach can generate new insights about the evolution, diagnosis, and treatment of threat-related psychopathology.

Human cerebral organoids establish subcortical projections in the mouse brain after transplantation

Numerous studies have used human pluripotent stem cell-derived cerebral organoids to elucidate the mystery of human brain development and model neurological diseases in vitro, but the potential for grafted organoid-based therapy in vivo remains unknown. Here, we optimized a culturing protocol capable of efficiently generating small human cerebral organoids. After transplantation into the mouse medial prefrontal cortex, the grafted human cerebral organoids survived and extended projections over 4.5 mm in length to basal brain regions within 1 month. The transplanted cerebral organoids generated human glutamatergic neurons that acquired electrophysiological maturity in the mouse brain. Importantly, the grafted human cerebral organoids functionally integrated into pre-existing neural circuits by forming bidirectional synaptic connections with the mouse host neurons. Furthermore, compared to control mice, the mice transplanted with cerebral organoids showed an increase in freezing time in response to auditory conditioned stimuli, suggesting the potentiation of the startle fear response. Our study showed that subcortical projections can be established by microtransplantation and may provide crucial insights into the therapeutic potential of human cerebral organoids for neurological diseases.

Distributed coding in auditory thalamus and basolateral amygdala upon associative fear learning

Associative fear learning is a fundamental learning mechanism that is crucial for an animal's survival. The amygdala's role in fear memory formation has been studied extensively and molecular, cell type and circuit-specific learning mechanisms as well as population level encoding of threatful stimuli within the amygdala are at the core of fear learning. Nevertheless, increasing evidence suggests that fear memories are acquired, stored and modulated by a distributed neuronal network across many brain areas. Here we review recent studies that particularly re-assessed the role of auditory/lateral thalamus, which is one synapse upstream of the lateral amygdala, required for fear learning and exhibits a striking functional resemblance and plasticity pattern to downstream amygdala neurons on the single cell level, yet distinct population level coding.

Deep brain stimulation modulates directional limbic connectivity in obsessive-compulsive disorder

Deep brain stimulation is effective for patients with treatment-refractory obsessive-compulsive disorder. Deep brain stimulation of the ventral anterior limb of the internal capsule rapidly improves mood and anxiety with optimal stimulation parameters. To understand these rapid effects, we studied functional interactions within the affective amygdala circuit. We compared resting state functional MRI data during chronic stimulation versus 1 week of stimulation discontinuation in patients, and obtained two resting state scans from matched healthy volunteers to account for test-retest effects. Imaging data were analysed using functional connectivity analysis and dynamic causal modelling. Improvement in mood and anxiety following deep brain stimulation was associated with reduced amygdala-insula functional connectivity. Directional connectivity analysis revealed that deep brain stimulation increased the impact of the ventromedial prefrontal cortex on the amygdala, and decreased the impact of the amygdala on the insula. These results highlight the importance of the amygdala circuit in the pathophysiology of obsessive-compulsive disorder, and suggest a neural systems model through which negative mood and anxiety are modulated by stimulation of the ventral anterior limb of the internal capsule for obsessive-compulsive disorder and possibly other psychiatric disorders.

Hierarchical models of pain: Inference, information-seeking, and adaptive control

Computational models of pain consider how the brain processes nociceptive information and allow mapping neural circuits and networks to cognition and behaviour. To date, they have generally have assumed two largely independent processes: perceptual inference, typically modelled as an approximate Bayesian process, and action control, typically modelled as a reinforcement learning process. However, inference and control are intertwined in complex ways, challenging the clarity of this distinction. Here, we consider how they may comprise a parallel hierarchical architecture that combines inference, information-seeking, and adaptive value-based control. This sheds light on the complex neural architecture of the pain system, and takes us closer to understanding from where pain 'arises' in the brain.

Motivational factors underlying aversive Pavlovian-instrumental transfer

While interest in active avoidance has recently been resurgent, many concerns relating to the nature of this form of learning remain unresolved. By separating stimulus and response acquisition, aversive Pavlovian-instrumental transfer can be used to measure the effect of avoidance learning on threat processing with more control than typical avoidance procedures. However, the motivational substrates that contribute to the aversive transfer effect have not been thoroughly examined. In three studies using rodents, the impact of a variety of aversive signals on shock-avoidance responding (i.e., two-way shuttling) was evaluated. Fox urine, as well as a tone paired with the delivery of the predator odor were insufficient modulatory stimuli for the avoidance response. Similarly, a signal for the absence of food did not generate appropriate aversive motivation to enhance shuttling. Only conditioned Pavlovian stimuli that had been paired with unconditioned threats were capable of augmenting shock-avoidance responding. This was true whether the signaled outcome was the same (e.g., shock) or different (e.g., klaxon) from the avoidance outcome (i.e., shock). These findings help to characterize the aversive transfer effect and provide a more thorough analysis of its generalization to warning signals for different kinds of threats. This feature of aversive motivation has not been demonstrated using conventional avoidance procedures and could be potentially useful for applying avoidance in treatment settings.

A Central Amygdala-Globus Pallidus Circuit Conveys Unconditioned Stimulus-Related Information and Controls Fear Learning

The central amygdala (CeA) is critically involved in a range of adaptive behaviors, including defensive behaviors. Neurons in the CeA send long-range projections to a number of extra-amygdala targets, but the functions of these projections remain elusive. Here, we report that a previously neglected CeA-to-globus pallidus external segment (GPe) circuit plays an essential role in classical fear conditioning. By anatomic tracing, in situ hybridization and channelrhodopsin (ChR2)-assisted circuit mapping in both male and female mice, we found that a subset of CeA neurons send projections to the GPe, and the majority of these GPe-projecting CeA neurons express the neuropeptide somatostatin. Notably, chronic inhibition of GPe-projecting CeA neurons with the tetanus toxin light chain (TeLC) completely blocks auditory fear conditioning. In vivo fiber photometry revealed that these neurons are selectively excited by the unconditioned stimulus (US) during fear conditioning. Furthermore, transient optogenetic inactivation or activation of these neurons selectively during US presentation impairs or promotes, respectively, fear learning. Our results suggest that a major function of GPe-projecting CeA neurons is to represent and convey US-related information through the CeA-GPe circuit, thereby regulating learning in fear conditioning.SIGNIFICANCE STATEMENT The central amygdala (CeA) has been implicated in the establishment of defensive behaviors toward threats, but the underlying circuit mechanisms remain unclear. Here, we found that a subpopulation of neurons in the CeA, which are mainly those that express the neuropeptide somatostatin, send projections to the globus pallidus external segment (GPe), and this CeA-GPe circuit conveys unconditioned stimulus (US)-related information during classical fear conditioning, thereby having an indispensable role in learning. Our results reveal a previously unknown circuit mechanism for fear learning.

Bidirectional control of fear memories by cerebellar neurons projecting to the ventrolateral periaqueductal grey

Fear conditioning is a form of associative learning that is known to involve different brain areas, notably the amygdala, the prefrontal cortex and the periaqueductal grey (PAG). Here, we describe the functional role of pathways that link the cerebellum with the fear network. We found that the cerebellar fastigial nucleus (FN) sends glutamatergic projections to vlPAG that synapse onto glutamatergic and GABAergic vlPAG neurons. Chemogenetic and optogenetic manipulations revealed that the FN-vlPAG pathway controls bi-directionally the strength of the fear memories, indicating an important role in the association of the conditioned and unconditioned stimuli, a function consistent with vlPAG encoding of fear prediction error. Moreover, FN-vlPAG projections also modulate extinction learning. We also found a FN-parafascicular thalamus pathway, which may relay cerebellar influence to the amygdala and modulates anxiety behaviors. Overall, our results reveal multiple contributions of the cerebellum to the emotional system.

The cerebellum has a role in motor control, but may also contribute to other functions. Here the authors demonstrate a role for the cerebellar fastigial nucleus projection onto ventrolateral periaqueductal grey neurons during fear acquisition.

Sex Differences in the Development of the Rodent Corticolimbic System

In recent years, a growing body of research has shown sex differences in the prevalence and symptomatology of psychopathologies, such as depression, anxiety, and fear-related disorders, all of which show high incidence rates in early life. This has highlighted the importance of including female subjects in animal studies, as well as delineating sex differences in neural processing across development. Of particular interest is the corticolimbic system, comprising the hippocampus, amygdala, and medial prefrontal cortex. In rodents, these corticolimbic regions undergo dynamic changes in early life, and disruption to their normative development is believed to underlie the age and sex-dependent effects of stress on affective processing. In this review, we consolidate research on sex differences in the hippocampus, amygdala, and medial prefrontal cortex across early development. First, we briefly introduce current principles on sexual differentiation of the rodent brain. We then showcase corticolimbic regional sex differences in volume, morphology, synaptic organization, cell proliferation, microglia, and GABAergic signaling, and explain how these differences are influenced by perinatal and pubertal gonadal hormones. In compiling this research, we outline evidence of what and when sex differences emerge in the developing corticolimbic system, and illustrate how temporal dynamics of its maturational trajectory may differ in male and female rodents. This will help provide insight into potential neural mechanisms underlying sex-specific critical windows for stress susceptibility and behavioral emergence.

Shared yet dissociable neural codes across eye gaze, valence and expectation

The direction of the eye gaze of others is a prominent social cue in primates and is important for communication^1-11. Although gaze can signal threat and elicit anxiety^6,12,13, it remains unclear whether it shares neural circuitry with stimulus value. Notably, gaze not only has valence, but can also serve as a predictor of the outcome of a social encounter, which can be either negative or positive^2,8,12,13. Here we show that the neural codes for gaze and valence overlap in primates and that they involve two different mechanisms: one for the outcome and another for its expectation. Monkeys participated in the human intruder test^13,14, in which a human participant had either a direct or averted gaze, interleaved with blocks of aversive and appetitive conditioning. We find that single neurons in the amygdala encode gaze¹⁵, whereas neurons in the anterior cingulate cortex encode the social context¹⁶, but not gaze. We identify a shared population in the amygdala for which the neural responses to direct and averted gaze parallel the responses to aversive and appetitive stimulus, respectively. Furthermore, we distinguish between two neural mechanisms-an overall-activity scheme that is used for gaze and the unconditioned stimulus, and a correlated-selectivity scheme that is used for gaze and the conditioned stimulus. These findings provide insights into the origins of the neural mechanisms that underlie the computations of both social interactions and valence, and could help to shed light on mechanisms that underlie social anxiety and the comorbidity between anxiety and impaired social interactions.

Individual differences in fear acquisition: multivariate analyses of different emotional negativity scales, physiological responding, subjective measures, and neural activation

Negative emotionality is a well-established and stable risk factor for affective disorders. Individual differences in negative emotionality have been linked to associative learning processes which can be captured experimentally by computing CS-discrimination values in fear conditioning paradigms. Literature suffers from underpowered samples, suboptimal methods, and an isolated focus on single questionnaires and single outcome measures. First, the specific and shared variance across three commonly employed questionnaires [STAI-T, NEO-FFI-Neuroticism, Intolerance of Uncertainty (IU) Scale] in relation to CS-discrimination during fear-acquisition in multiple analysis units (ratings, skin conductance, startle) is addressed (NStudy1 = 356). A specific significant negative association between STAI-T and CS-discrimination in SCRs and between IU and CS-discrimination in startle responding was identified in multimodal and dimensional analyses, but also between latent factors negative emotionality and fear learning, which capture shared variance across questionnaires/scales and across outcome measures. Second, STAI-T was positively associated with CS-discrimination in a number of brain areas linked to conditioned fear (amygdala, putamen, thalamus), but not to SCRs or ratings (NStudy2 = 113). Importantly, we replicate potential sampling biases between fMRI and behavioral studies regarding anxiety levels. Future studies are needed to target wide sampling distributions for STAI-T and verify whether current findings are generalizable to other samples.

Kainate Receptor Auxiliary Subunit NETO2-Related Cued Fear Conditioning Impairments Associate with Defects in Amygdala Development and Excitability

NETO2 is an auxiliary subunit for kainate-type glutamate receptors that mediate normal cued fear expression and extinction. Since the amygdala is critical for these functions, we asked whether Neto2 ^-/- mice have compromised amygdala function. We measured the abundance of molecular markers of neuronal maturation and plasticity, parvalbumin-positive (PV⁺), perineuronal net-positive (PNN⁺), and double positive (PV⁺PNN⁺) cells in the Neto2 ^-/- amygdala. We found that Neto2 ^-/- adult, but not postnatal day (P)23, mice had 7.5% reduction in the fraction of PV⁺PNN⁺ cells within the total PNN⁺ population, and 23.1% reduction in PV staining intensity compared with Neto2 ^+/+ mice, suggesting that PV interneurons in the adult Neto2 ^-/- amygdala remain in an immature state. An immature PV inhibitory network would be predicted to lead to stronger amygdalar excitation. In the amygdala of adult Neto2 ^-/- mice, we identified increased glutamatergic and reduced GABAergic transmission using whole-cell patch-clamp recordings. This was accompanied by increased spine density of thin dendrites in the basal amygdala (BA) compared with Neto2 ^+/+ mice, indicating stronger glutamatergic synapses. Moreover, after fear acquisition Neto2 ^-/- mice had a higher number of c-Fos-positive cells than Neto2 ^+/+ mice in the lateral amygdala (LA), BA, and central amygdala (CE). Altogether, our findings indicate that Neto2 is involved in the maturation of the amygdala PV interneuron network. Our data suggest that this defect, together with other processes influencing amygdala principal neurons, contribute to increased amygdalar excitability, higher fear expression, and delayed extinction in cued fear conditioning, phenotypes that are common in fear-related disorders, including the posttraumatic stress disorder (PTSD).

Neurotrophin signalling in amygdala-dependent cued fear learning

The amygdala is a central hub for fear learning assessed by Pavlovian fear conditioning. Indeed, the prevailing hypothesis that learning and memory are mediated by changes in synaptic strength was shown most convincingly at thalamic and cortical afferents to the lateral amygdala. The neurotrophin brain-derived neurotrophic factor (BDNF) is known to regulate synaptic plasticity and memory formation in many areas of the mammalian brain including the amygdala, where BDNF signalling via tropomyosin-related kinase B (TrkB) receptors is prominently involved in fear learning. This review updates the current understanding of BDNF/TrkB signalling in the amygdala related to fear learning and extinction. In addition, actions of proBDNF/p75NTR and NGF/TrkA as well as NT-3/TrkC signalling in the amygdala are introduced.

Affective Cortical Asymmetry at the Early Developmental Emergence of Emotional Expression

Emotions have an important survival function. Vast amounts of research have demonstrated how affect-related changes in physiology promote survival by effecting short-term and long-term changes in adaptive behavior. However, if emotions truly serve such an inherent function, they should be pervasive across species and be established early in life. Here, using electroencephalographic (EEG) brain activity we sought to characterize core neurophysiological features underlying affective function at the emergence of emotional expression [i.e., at the developmental age when human infants start to show reliable stimulus-elicited emotional states (4–6 months)]. Using an approach that eschews traditional EEG frequency band delineations (like theta, alpha), we demonstrate that negative emotional states induce a strong right hemispheric increase in the prominence of the resonant frequency (∼5–6 Hz) in the infant frontal EEG. Increased rightward asymmetry was strongly correlated with increased heart rate responses to emotionally negative states compared with neutral states. We conclude that functional frontal asymmetry is a key component of emotional processing and suggest that the rightward asymmetry in prominence of the resonant frequency during negative emotional states might reflect functional asymmetry in the central representation of anatomically driven asymmetry in the autonomic nervous system. Our findings indicate that the specific mode hallmarking emotional processing in the frontal cortex is established in parallel with the emergence of stable emotional states very early during development, despite the well known protracted maturation of frontal cortex.

Predicting susceptibility and resilience in an animal model of post-traumatic stress disorder (PTSD)

Post-traumatic stress disorder (PTSD) is a psychiatric disorder whose pathogenesis relies on a maladaptive expression of the memory for a life-threatening experience, characterized by over-consolidation, generalization, and impaired extinction, which are responsible of dramatic changes in arousal, mood, anxiety, and social behavior. Even if subjects experiencing a traumatic event during lifetime all show an acute response to the trauma, only a subset of them (susceptible) ultimately develops PTSD, meanwhile the others (resilient) fully recover after the first acute response. However, the dynamic relationships between the interacting brain circuits that might potentially link trauma-related experiences to the emergence of susceptible and resilient PTSD phenotypes in individuals is not well understood. Toward the first step to reach this goal, we have implemented our experimental PTSD model previously developed, making it suitable to differentiate between susceptible (high responders, HR) and resilient (low responders, LR) rats in terms of over-consolidation, impaired extinction, and social impairment long after trauma. Rats were exposed to five footshocks paired with social isolation. One week after trauma but before extinction, animals were tested in the Open Field and Social Interaction tasks for the identification of a predictive variable to identify susceptible and resilient animals before the possible appearance of a PTSD-like phenotype. Our findings show that exploratory activity after trauma in a novel environment is a very robust variable to predict susceptibility towards a PTSD-like phenotype. This experimental model is thus able to screen and differentiate, before extinction learning and potential therapeutic intervention, susceptible and resilient PTSD-like rats.

Contextual fear memory retrieval by correlated ensembles of ventral CA1 neurons

Ventral hippocampal CA1 (vCA1) projections to the amygdala are necessary for contextual fear memory. Here we used in vivo Ca2+ imaging in mice to assess the temporal dynamics by which ensembles of vCA1 neurons mediate encoding and retrieval of contextual fear memories. We found that a subset of vCA1 neurons were responsive to the aversive shock during context conditioning, their activity was necessary for memory encoding, and these shock-responsive neurons were enriched in the vCA1 projection to the amygdala. During memory retrieval, a population of vCA1 neurons became correlated with shock-encoding neurons, and the magnitude of synchronized activity within this population was proportional to memory strength. The emergence of these correlated networks was disrupted by inhibiting vCA1 shock responses during memory encoding. Thus, our findings suggest that networks of cells that become correlated with shock-responsive neurons in vCA1 are essential components of contextual fear memory ensembles.

Learning-related population dynamics in the auditory thalamus

Learning to associate sensory stimuli with a chosen action involves a dynamic interplay between cortical and thalamic circuits. While the cortex has been widely studied in this respect, how the thalamus encodes learning-related information is still largely unknown. We studied learning-related activity in the medial geniculate body (MGB; Auditory thalamus), targeting mainly the dorsal and medial regions. Using fiber photometry, we continuously imaged population calcium dynamics as mice learned a go/no-go auditory discrimination task. The MGB was tuned to frequency and responded to cognitive features like the choice of the mouse within several hundred milliseconds. Encoding of choice in the MGB increased with learning, and was highly correlated with the learning curves of the mice. MGB also encoded motor parameters of the mouse during the task. These results provide evidence that the MGB encodes task- motor- and learning-related information.

General anesthetics activate a potent central pain-suppression circuit in the amygdala

General anesthesia (GA) can produce analgesia (loss of pain) independent of inducing loss of consciousness, but the underlying mechanisms remain unclear. We hypothesized that GA suppresses pain in part by activating supraspinal analgesic circuits. We discovered a distinct population of GABAergic neurons activated by GA in the mouse central amygdala (CeA_GA neurons). In vivo calcium imaging revealed that different GA drugs activate a shared ensemble of CeA_GA neurons. CeA_GA neurons also possess basal activity that mostly reflects animals' internal state rather than external stimuli. Optogenetic activation of CeA_GA potently suppressed both pain-elicited reflexive and self-recuperating behaviors across sensory modalities and abolished neuropathic pain-induced mechanical (hyper-)sensitivity. Conversely, inhibition of CeA_GA activity exacerbated pain, produced strong aversion and canceled the analgesic effect of low-dose ketamine. CeA_GA neurons have widespread inhibitory projections to many affective pain-processing centers. Our study points to CeA_GA as a potential powerful therapeutic target for alleviating chronic pain.

Anticipatory Threat Responding: Associations With Anxiety, Development, and Brain Structure

BACKGROUND

While translational theories link neurodevelopmental changes in threat learning to pathological anxiety, findings from studies in patients inconsistently support these theories. This inconsistency may reflect difficulties in studying large patient samples with wide age ranges using consistent methods. A dearth of imaging data in patients further limits translational advances. We address these gaps through a psychophysiology and structural brain imaging study in a large sample of patients across the lifespan.

METHODS

A total of 351 participants (8-50 years of age; 209 female subjects; 195 healthy participants and 156 medication-free, treatment-seeking patients with anxiety) completed a differential threat conditioning and extinction paradigm that has been validated in pediatric and adult populations. Skin conductance response indexed psychophysiological response to conditioned (CS+, CS-) and unconditioned threat stimuli. Structural magnetic resonance imaging data were available for 250 participants. Analyses tested anxiety and age associations with psychophysiological response in addition to associations between psychophysiology and brain structure.

RESULTS

Regardless of age, patients and healthy comparison subjects demonstrated comparable differential threat conditioning and extinction. The magnitude of skin conductance response to both conditioned stimulus types differentiated patients from comparison subjects and covaried with dorsal prefrontal cortical thickness; structure-response associations were moderated by anxiety and age in several regions. Unconditioned responding was unrelated to anxiety and brain structure.

CONCLUSIONS

Rather than impaired threat learning, pathological anxiety involves heightened skin conductance response to potential but not immediately present threats; this anxiety-related potentiation of anticipatory responding also relates to variation in brain structure. These findings inform theoretical considerations by highlighting anticipatory response to potential threat in anxiety.

Beyond Freezing: Temporal Expectancy of an Aversive Event Engages the Amygdalo–Prefronto–Dorsostriatal Network

During Pavlovian aversive conditioning, a neutral conditioned stimulus (CS) becomes predictive of the time of arrival of an aversive unconditioned stimulus (US). Using a paradigm where animals had to discriminate between a CS+ (associated with a footshock) and a CS− (never associated with a footshock), we show that, early in training, dynamics of neuronal oscillations in an amygdalo–prefronto–striatal network are modified during the CS+ in a manner related to the CS–US time interval (30 or 10 s). This is the case despite a generalized high level of freezing to both CS+ and CS−. The local field potential oscillatory power was decreased between 12 and 30 Hz in the dorsomedial striatum (DMS) and increased between 55 and 95 Hz in the prelimbic cortex (PL), while the coherence between DMS, PL, and the basolateral amygdala was increased in the 3–6 Hz frequency range up to the expected time of US arrival only for the CS+ and not for the CS−. Changing the CS–US interval from 30 to 10 s shifted these changes in activity toward the newly learned duration. The results suggest a functional role of the amygdalo–prefronto–dorsostriatal network in encoding temporal information of Pavlovian associations independently of the behavioral output.

Thalamic, cortical, and amygdala involvement in the processing of a natural sound cue of danger

Animals use auditory cues generated by defensive responses of others to detect impending danger. Here we identify a neural circuit in rats involved in the detection of one such auditory cue, the cessation of movement-evoked sound resulting from freezing. This circuit comprises the dorsal subnucleus of the medial geniculate body (MGD) and downstream areas, the ventral area of the auditory cortex (VA), and the lateral amygdala (LA). This study suggests a role for the auditory offset pathway in processing a natural sound cue of threat.

A VTA to Basal Amygdala Dopamine Projection Contributes to Signal Salient Somatosensory Events during Fear Learning

The amygdala is a brain area critical for the formation of fear memories. However, the nature of the teaching signal(s) that drive plasticity in the amygdala are still under debate. Here, we use optogenetic methods to investigate the contribution of ventral tegmental area (VTA) dopamine neurons to auditory-cued fear learning in male mice. Using anterograde and retrograde labeling, we found that a sparse and relatively evenly distributed population of VTA neurons projects to the basal amygdala (BA). In vivo optrode recordings in behaving mice showed that many VTA neurons, among them putative dopamine neurons, are excited by footshocks, and acquire a response to auditory stimuli during fear learning. Combined cfos imaging and retrograde labeling in dopamine transporter (DAT) Cre mice revealed that a large majority of BA projectors (>95%) are dopamine neurons, and that BA projectors become activated by the tone-footshock pairing of fear learning protocols. Finally, silencing VTA dopamine neurons, or their axon terminals in the BA during the footshock, reduced the strength of fear memory as tested 1 d later, whereas silencing the VTA-central amygdala (CeA) projection had no effect. Thus, VTA dopamine neurons projecting to the BA contribute to fear memory formation, by coding for the saliency of the footshock event and by signaling such events to the basal amygdala.SIGNIFICANCE STATEMENT Powerful mechanisms of fear learning have evolved in animals and humans to enable survival. During fear conditioning, a sensory cue, such as a tone (the conditioned stimulus), comes to predict an innately aversive stimulus, such as a mild footshock (the unconditioned stimulus). A brain representation of the unconditioned stimulus must act as a teaching signal to instruct plasticity of the conditioned stimulus representation in fear-related brain areas. Here we show that dopamine neurons in the VTA that project to the basal amygdala contribute to such a teaching signal for plasticity, thereby facilitating the formation of fear memories. Knowledge about the role of dopamine in aversively motivated plasticity might allow further insights into maladaptive plasticities that underlie anxiety and post-traumatic stress disorders in humans.

Kainate receptors regulate development of glutamatergic synaptic circuitry in the rodent amygdala

Perturbed information processing in the amygdala has been implicated in developmentally originating neuropsychiatric disorders. However, little is known on the mechanisms that guide formation and refinement of intrinsic connections between amygdaloid nuclei. We demonstrate that in rodents the glutamatergic connection from basolateral to central amygdala (BLA-CeA) develops rapidly during the first 10 postnatal days, before external inputs underlying amygdala-dependent behaviors emerge. During this restricted period of synaptic development, kainate-type of ionotropic glutamate receptors (KARs) are highly expressed in the BLA and tonically activated to regulate glutamate release via a G-protein-dependent mechanism. Genetic manipulation of this endogenous KAR activity locally in the newborn LA perturbed development of glutamatergic input to CeA, identifying KARs as a physiological mechanism regulating formation of the glutamatergic circuitry in the amygdala.

Role of lateral amygdala calstabin2 in regulation of fear memory

Calstabin2, also named FK506 binding protein 12.6 (FKBP12.6), is a subunit of ryanodine receptor subtype 2 (RyR2) macromolecular complex, an intracellular calcium channel. Studies from our and other's lab have shown that hippocampal calstabin2 regulates spatial memory. Calstabin2 and RyR2 are widely distributed in the brain, including the amygdala, a key brain area involved in the regulation of emotion including fear. Little is known about the role of calstabin2 in fear memory. Here, we found that genetic deletion of calstabin2 impaired long-term memory in cued fear conditioning test. Knockdown calstabin2 in the lateral amygdala (LA) by viral vector also impaired long-term cued fear memory expression. Furthermore, calstabin2 knockout reduced long-term potentiation (LTP) at both cortical and thalamic inputs to the LA. In conclusion, our present data indicate that calstabin2 in the LA plays a crucial role in the regulating of emotional memory.

Visuocortical tuning to a threat-related feature persists after extinction and consolidation of conditioned fear

Neurons in the visual cortex sharpen their orientation tuning as humans learn aversive contingencies. A stimulus orientation (CS+) that reliably predicts an aversive noise (unconditioned stimulus: US) is selectively enhanced in lower-tier visual cortex, while similar unpaired orientations (CS-) are inhibited. Here, we examine in male volunteers how sharpened visual processing is affected by fear extinction learning (where no US is presented), and how fear and extinction memory undergo consolidation one day after the original learning episode. Using steady-state visually evoked potentials from electroencephalography in a fear generalization task, we found that extinction learning prompted rapid changes in orientation tuning: Both conditioned visuocortical and skin conductance responses to the CS+ were strongly reduced. Next-day re-testing (delayed recall) revealed a brief but precise return-of-tuning to the CS+ in visual cortex accompanied by a brief, more generalized return-of-fear in skin conductance. Explorative analyses also showed persistent tuning to the threat cue in higher visual areas, 24 h after successful extinction, outlasting peripheral responding. Together, experience-based changes in the sensitivity of visual neurons show response patterns consistent with memory consolidation and spontaneous recovery, the hallmarks of long-term neural plasticity.

Phasic signaling in the bed nucleus of the stria terminalis during fear learning predicts within- and across-session cued fear expression

While results from many past studies have implicated the bed nucleus of the stria terminalis (BNST) in mediating the expression of sustained negative affect, recent studies have highlighted a more complex role for BNST that includes aspects of fear learning in addition to defensive responding. As BNST is thought to encode ambiguous or unpredictable threat, it seems plausible that it may be involved in encoding early cued fear learning, especially immediately following a first tone-shock pairing when the conditioned stimulus–unconditioned stimulus (CS–US) contingency is not fully apparent. To investigate this, we conducted in vivo electrophysiological recording studies to examine neural dynamics of BNST units during cued fear acquisition and recall. We identified two functionally distinct subpopulations of BNST neurons that encode the intertrial interval (ITI) and may contribute to within- and across-session fear learning. “Ramping” cell activity during cued fear acquisition parallels the increase in freezing expression as mice learn the CS–US contingency, while “Phasic” cells encode postshock (US_post) periods (30 sec following encounter with footshock) only during early trials. Importantly, the magnitude of Phasic unit responsivity to the first US_post period predicted not only freezing expression in response to the subsequent CS during acquisition, but also CS freezing evoked 24 h later during CS retrieval. These findings suggest for the first time that BNST activity may serve as an instructive signal during cued fear learning.

Basolateral Amygdala Connectivity With Subgenual Anterior Cingulate Cortex Represents Enhanced Fear-Related Memory Encoding in Anxious Humans

BACKGROUND

The amygdala can enhance emotional memory encoding as well as anxiogenesis via corticotropin-releasing factor neurons. However, the amygdala's explicit role in emotional encoding remains unclarified in humans. We examined how functional connectivity (FC) of amygdala subnuclei affects emotional encoding, considering its mechanism in which anxiety, attention, and cortisol conceivably participate.

METHODS

A total of 65 healthy humans underwent resting-state functional magnetic resonance imaging scans and saliva collection at 10 points in time over 2 days. FC analysis was performed for basolateral amygdala subnucleus (BLA) and centromedial amygdala subnucleus. We assessed attentional control via an emotional Stroop task and assessed emotional encoding via a facial identification task that examines how strongly a neutral face is memorized when accompanied by an emotional face (fearful, sad, or happy). FC and task performance were compared between high-anxious and non-high-anxious groups classified by anxious personality scores.

RESULTS

BLA connected with subgenual anterior cingulate cortex (sgACC) in proportion to the strength of fear-related encoding, whereas centromedial subnucleus connected with caudate nucleus for happy-related encoding. The high-anxious group showed more enhanced fear-related encoding but impaired happy-related encoding compared with the non-high-anxious group. BLA-sgACC FC was more intensified in the high-anxious group than in the non-high-anxious group; however, centromedial-caudate FC did not differ between them. Although emotional encoding was uncorrelated with either attentional control or cortisol, BLA-sgACC was positively correlated with cortisol increase after awakening.

CONCLUSIONS

The study revealed that neural interactions of BLA, specifically with sgACC, might play a critical role in fear-related memory encoding, depending on the individual's level of anxiety. These findings aid in understanding the complicated mechanisms of emotional memory in anxiety disorders.

A brainstem-central amygdala circuit underlies defensive responses to learned threats

Norepinephrine (NE) plays a central role in the acquisition of aversive learning via actions in the lateral nucleus of the amygdala (LA) [1, 2]. However, the function of NE in expression of aversively-conditioned responses has not been established. Given the role of the central nucleus of the amygdala (CeA) in the expression of such behaviors [3-5], and the presence of NE axons projections in this brain nucleus [6], we assessed the effects of NE activity in the CeA on behavioral expression using receptor-specific pharmacology and cell- and projection-specific chemogenetic manipulations. We found that inhibition and activation of locus coeruleus (LC) neurons decreases and increases freezing to aversively conditioned cues, respectively. We then show that locally inhibiting or activating LC terminals in CeA is sufficient to achieve this bidirectional modulation of defensive reactions. These findings support the hypothesis that LC projections to CeA are critical for the expression of defensive responses elicited by conditioned threats.

Amygdala GluN2B-NMDAR dysfunction is critical in abnormal aggression of neurodevelopmental origin induced by St8sia2 deficiency

Aggression is frequently observed in neurodevelopmental psychiatric disorders such as schizophrenia, autism, and bipolar disorder. Due to a lack of understanding of its underlying mechanisms, effective treatments for abnormal aggression are still missing. Recently, genetic variations in Sialyltransferase 2 (St8sia2) have been linked to these disorders and aggression. Here we identify abnormal aggressive behaviors and concomitant blunted fear learning in St8sia2 knockout (-/-) mice. It is worth noting that the amygdala of St8sia2-/- mice shows diminished threat-induced activation, as well as alterations in synaptic structure and function, including impaired GluN2B-containing NMDA receptor-mediated synaptic transmission and plasticity. Pharmacological rescue of NMDA receptor activity in the amygdala of St8sia2-/- mice with the partial agonist D-cycloserine restores synaptic plasticity and normalizes behavioral aberrations. Pathological aggression and associated traits were recapitulated by specific amygdala neonatal St8sia2 silencing. Our results establish a developmental link between St8sia2 deficiency and a pathological aggression syndrome, specify synaptic targets for therapeutic developments, and highlight D-cycloserine as a plausible treatment.

The neural processes of acquiring placebo effects through observation

Learning through social observation is critical for humans. The present study investigates the neural processes underlying the acquisition of placebo effects through observational learning. We created a new functional magnetic resonance imaging (fMRI) paradigm where participants (n ​= ​38, healthy, both sexes) observed a demonstrator experiencing pain relief by a placebo treatment cream and experiencing pain without a treatment (control cream), and subsequently performed the same procedure themselves. Participants demonstrated placebo hypoalgesia while they performed the procedure themselves, confirming that observational learning can lead to placebo effects. During the observational learning phase, fMRI analysis showed a modulation of the amygdalae, periaqueductal grey, temporoparietal junctions (TPJ), and dorsolateral prefrontal cortex (DLPFC). Connectivity between the DLPFC and TPJ during the observational learning task was modulated by the placebo treatment and predicted subsequent placebo effects. Mediation analysis further confirmed that the DLPFC-TPJ connectivity formally mediated the effect of the observed treatment condition on subsequent placebo effects. Additionally, pre-recorded resting state connectivity between the DLPFC and TPJ also predicted observationally-learned placebo effects. Our findings provide an understanding of the neural processes during the acquisition of placebo effects through observation and indicate a critical role for DLPFC-TPJ integration processes during observational learning of therapeutic outcomes.

Prefrontal somatostatin interneurons encode fear memory

Theories stipulate that memories are encoded within networks of cortical projection neurons. Conversely, GABAergic interneurons are thought to function primarily to inhibit projection neurons and thereby impose network gain control, an important but purely modulatory role. Here we show in male mice that associative fear learning potentiates synaptic transmission and cue-specific activity of medial prefrontal cortex somatostatin (SST) interneurons and that activation of these cells controls both memory encoding and expression. Furthermore, the synaptic organization of SST and parvalbumin interneurons provides a potential circuit basis for SST interneuron-evoked disinhibition of medial prefrontal cortex output neurons and recruitment of remote brain regions associated with defensive behavior. These data suggest that, rather than constrain mnemonic processing, potentiation of SST interneuron activity represents an important causal mechanism for conditioned fear.

Does case-based blended-learning expedite the transfer of declarative knowledge to procedural knowledge in practice?

BACKGROUND

Case-Based Learning (CBL) has seen widespread implementation in undergraduate education since the early 1920s. Ample data has shown CBL to be an enjoyable and motivational didactic tool, and effective in assisting the expansion of declarative and procedural knowledge in academia. Although a plethora of studies apply multiple choice questions (MCQs) in their investigation, few studies measure CBL or case-based blended learning (CBBL)-mediated changes in students' procedural knowledge in practice or employ comparison or control groups in isolating causal relationships.

METHODS

Utilizing the flexibilities of an e-learning platform, a CBBL framework consisting of a) anonymized patient cases, b) case-related textbook material and online e-CBL modules, and c) simulated patient (SP) contact seminars, was developed and implemented in multiple medical fields for undergraduate medical education. Additionally, other fields saw a solo implementation of e-CBL in the same format. E- cases were constructed according to the criteria of Bloom's taxonomy. In this study, Objective Structured Clinical Examination (OSCE) results from 1886 medical students were analyzed in total, stratified into the following groups: medical students in 2013 (n = 619) before CBBL implementation, and after CBBL implementation in 2015 (n = 624) and 2016 (n = 643).

RESULTS

A significant improvement (adjusted p = .002) of the mean OSCE score by 1.02 points was seen between 2013 and 2015 (min = 0, max = 25).

CONCLUSION

E-Case-Based Learning is an effective tool in improving performance outcomes and may provide a sustainable learning platform for many fields of medicine in future.