Fear extinction as a model for translational neuroscience: ten years of progress

Different protocols of REM sleep deprivation led to controversial effects on OCD- and anxiety-like behaviors and locomotor activity in fear conditioning male and female rats with respect to BDNF expression level

Specific protocols of rapid-eye movement (REM) sleep deprivation (SD) may lead to behavioral phenotypes considered as obsessive-compulsive disorder (OCD)-like behavior and hyperactivity (mania-like behavior). The present study aimed to assess the effects of REM SD on both sexes of control and fear conditioning (FC) rats. REM SD was induced for 1 or 2 or 3 weeks (6 h/d). Freezing, locomotor activity, anxiety-like behavior, grooming and burying marbles (OCD-like behaviors), and brain-derived neurotrophic factor (BDNF) in the hippocampus were evaluated. The results showed 1w REM SD decreased freezing in females, while 2w and 3w REM SD decreased freezing in both sexes. Locomotor activity in 2w REM SD males was increased, while was decreased in 3w group. In females, both 2w and 3w REM SD increased locomotion. REM SD in both sexes increased locomotion in FC rats. All REM SD protocols decreased anxiety in both sexes of FC rats. REM SD in control and FC rats led to OCD-like behaviors. All REM SD protocols decreased BDNF in both sexes, while 3w slightly increased it, suggesting a compensatory mechanism over time. 2w and 3w REM SD increased BDNF in FC rats in both sexes. Pearson correlation test also showed that changes in BDNF levels may be related to some behavioral changes only in females. In conclusion, for the first time, the present study showed sex differences in the effects of REM SD on behavioral functions in control and FC rats, and in the relationship between BDNF levels and behavioral changes.

Developmental differences in threat learning are associated with changes in frontal-central theta activity

Major theories link variations in threat learning to the emergence of anxiety symptoms, especially during adolescence. Despite significant neural maturation of threat learning circuitry during this developmental stage, research on adolescence-specific neural responses during threat learning is limited. This study was the first to examine threat learning mechanisms through neural frequency activity among youth, focusing on activity in the theta (4-7 Hz) and alpha (8-12 Hz) frequency bands. Sixty-three adolescents and 65 adults completed a two-day threat acquisition and extinction procedure, while brain activity was measured using electroencephalography (EEG). Analyses focused on developmental differences in high temporal resolution changes in frequency activity, distinguishing between induced and evoked EEG signals. Developmental differences were mainly observed in frontal-central theta activity. During acquisition, adolescents showed higher induced theta activity to both threat and safety cues than adults. During extinction, adults showed decreased evoked theta activity to the conditioned stimulus, indicating effective inhibition of threat representations; in contrast, adolescents exhibited persistent threat contingencies throughout extinction. Both groups showed consistent alpha suppression towards the threat cue, suggesting sustained vigilance even during late extinction. Frontal-central theta activity is a valuable marker for capturing differences between adolescents and adults in threat learning. These findings add to mechanistic research efforts aiming to uncover factors contributing to anxiety vulnerability during adolescence.

Hippocampal ensembles regulate circuit-induced relapse of extinguished fear

Extinction learning is central to behavioral therapies for post-traumatic stress disorder (PTSD), but relapse poses a major challenge to this approach. Recent work has revealed a critical role for the thalamic nucleus reuniens (RE) in the suppression of extinguished fear memories. Silencing the RE yields a relapse of extinguished fear (i.e., "circuit-induced relapse"). Considerable work suggests that RE may contribute to extinction by inhibiting the retrieval of hippocampal (HPC)-dependent fear memories. To test this hypothesis, we first examined whether undermining the formation of contextual fear memories in the HPC would prevent circuit-induced relapse. Intra-hippocampal infusions of the NMDA receptor antagonist, APV, prior to auditory fear conditioning eliminated contextual fear memory and prevented the subsequent relapse of extinguished fear to the auditory conditioned stimulus (CS). In a second experiment, we used an activity-dependent labeling system (AAV-cFos-tTA; AAV-TRE-hM3Dq-mCherry) to express excitatory DREADDs in HPC neurons during fear conditioning. Chemogenetic reactivation of these ensembles after extinction was sufficient to drive relapse of fear to the extinguished CS. Lastly, in a third experiment, we expressed excitatory DREADDs in HPC ensembles captured during extinction learning and found that chemogenetic reactivation of this ensemble was sufficient to inhibit circuit-induced relapse. These results reveal that HPC-dependent ensembles play a critical role in regulating the expression and relapse of extinguished fear.

Mild Traumatic Brain Injury Impairs Fear Extinction and Network Excitability in the Infralimbic Cortex

Traumatic brain injury (TBI) is a leading cause of morbidity and disability, with mild TBI (concussions) representing over 80% of cases. Although often considered benign, mild TBI is associated with persistent neuropsychiatric conditions, including post-traumatic stress disorder, anxiety, and depression. A hallmark of these conditions is impaired fear extinction (FE), the process by which learned fear responses are inhibited in safe contexts. This dysfunction contributes to maladaptive fear expression and is linked to altered neurocircuitry, particularly in the infralimbic cortex (IL), a key region in FE. Despite extensive evidence of impaired FE in patients with mild TBI and animal models, the specific mechanisms underlying this deficit remain poorly understood. This study aimed to address this gap by combining cued-FE behavior, local field potential recordings, and whole-cell patch-clamp techniques to investigate how mild TBI affects IL network activity and excitability in a mouse model of TBI. Our results demonstrate that mild lateral fluid percussion injury significantly impairs FE memory, as evidenced by an elevated cued-fear response during extinction testing 10 days post-injury. Field potential recordings revealed decreased activation of the IL network in both layers II/III and V, which was consistent with the observed behavioral deficits. Further analysis of synaptic physiology revealed an imbalance in excitatory and inhibitory neurotransmission (E/I imbalance) in the IL, characterized by reduced excitatory input and enhanced inhibitory input to neurons in both layers. Moreover, intrinsic excitability was altered in IL neurons after mild TBI. This study provides novel insights into how mild TBI disrupts the neurocircuitry underlying FE, specifically by suppressing IL excitability. These results highlight the importance of understanding the mechanistic disruptions in IL activity for developing therapeutic strategies to address fear-based disorders in patients with mild TBI.

Expanding the toolset of experimental Psychopathology: The Trier Social Stress Test induces a personally relevant emotional memory

Despite the remarkable progress in developing effective psychological interventions for emotional disorders, our understanding of the mechanisms driving therapeutic change remains strikingly limited. To bridge this gap, we need to refine experimental paradigms with high ecological validity and establish their clinical utility. In this study, we replicate and extend previous findings that the Trier Social Stress Test (TSST) can evoke persistent, sensory rich, and personally meaningful emotional memories. One week after the TSST, a student sample (N = 146) reported greater negative valence, arousal, and lack of control in response to TSST-related versus control cues. Participants reported intrusive memories, the content of which reflects the personal relevance, sensory richness, and emotionality of the TSST memory. Re-imagining the TSST through guided imagery evoked heightened emotional responses (skin conductance, heart rate, and self-report) and participants evaluated themselves more negatively due to the TSST. These effects correlated with trait anxiety. However, comparisons to a naïve sample that only experienced the TSST through guided imagery (N = 38) revealed that some findings, including changes in self-image, were not memory-induced. We conclude with concrete examples of how the paradigm can expand our toolset to further unravel mechanistic underpinnings of memory-focused interventions.

Utilizing rewards to dampen fear and its recovery

Fearful memories can be extinguished by repeated exposure, without aversive outcomes. Fear extinction as the basis for exposure therapy, is a common treatment for anxiety and fear-related disorders, but it can be unpleasant and does not always work. In two independent studies, we investigated whether a novel compound extinction procedure (simultaneous presentation of a rewarded and a feared stimulus, reward-fear deepened extinction) attenuates fear while tracking physiological, neural and subjective changes in pleasantness. The reward-fear deepened extinction showed comparable effects to the fear-fear deepened extinction (two-fear compound extinction) in effectively enhancing fear extinction and protecting against the return of fear 1 week later. Moreover, fear extinction accompanying a reward cue was perceived as more pleasant. On the neural level, we identified a network involving hippocampus and amygdala that underlies the benefit of deepened extinction, where connectivity changes also predicted changes in subjective pleasantness. Our study identifies the effects of deepened extinction in regulating long-term fear recovery and its underlying neural mechanism. We shed light on an innovative method to enhance fear extinction, with high translational potential for therapy.

Mechanisms of alcohol influence on fear conditioning: A computational model

BACKGROUND

A connection between stress-related illnesses and alcohol use disorders is extensively documented. Fear conditioning is a standard procedure used to study stress learning and links it to the activation of amygdala circuitry. However, the connection between the changes in amygdala circuitry and function induced by alcohol and fear conditioning is not well established.

METHODS

We introduce a computational model to test the mechanistic relationship between amygdala functional and circuit adaptations during fear conditioning and the impact of acute vs. repeated alcohol exposure. Using firing rate formalism, the model generates electrophysiological and behavioral responses in fear conditioning protocols via plasticity of amygdala inputs. The influence of alcohol is modeled by accounting for known modulation of connections within amygdala circuits, which consequently affect plasticity. Thus, the model connects the electrophysiological and behavioral experiments. We hypothesize that alterations within amygdala circuitry produced by alcohol cause abnormal plasticity of amygdala inputs such that fear extinction is slower to achieve and less robust.

RESULTS

In accordance with prior experimental results, both acute and prior repeated alcohol decrease the speed and robustness of fear extinction in our simulations. The model predicts that, first, the delay in fear extinction caused by alcohol is mostly induced by greater activation of the basolateral amygdala (BLA) after fear acquisition due to alcohol-induced modulation of synaptic weights. Second, both acute and prior repeated alcohol shift the amygdala network away from the robust extinction regime by inhibiting activity in the central amygdala (CeA). Third, our model predicts that fear memories formed during acute or after chronic alcohol are more connected to the context.

CONCLUSIONS

The model suggests how circuit changes induced by alcohol may affect fear behaviors and provides a framework for investigating the involvement of multiple neuromodulators in this neuroadaptive process.

Prefrontal encoding of an internal model for emotional inference

A key function of brain systems mediating emotion is to learn to anticipate unpleasant experiences. Although organisms readily associate sensory stimuli with aversive outcomes, higher-order forms of emotional learning and memory require inference to extrapolate the circumstances surrounding directly experienced aversive events to other indirectly related sensory patterns that were not part of the original experience. This type of learning requires internal models of emotion, which flexibly track directly experienced and inferred aversive associations. Although the brain mechanisms of simple forms of aversive learning have been well studied in areas such as the amygdala1-4, whether and how the brain forms and represents internal models of emotionally relevant associations are not known5. Here we report that neurons in the rodent dorsomedial prefrontal cortex (dmPFC) encode a flexible internal model of emotion by linking sensory stimuli in the environment with aversive events, whether they were directly or indirectly associated with that experience. These representations form through a multi-step encoding mechanism involving recruitment and stabilization of dmPFC cells that support inference. Although dmPFC population activity encodes all salient associations, dmPFC neurons projecting to the amygdala specifically represent and are required to express inferred associations. Together, these findings reveal how internal models of emotion are encoded in the dmPFC to regulate subcortical systems for recall of inferred emotional memories.

Effects of pregnancy on neuron electrophysiology in prefrontal cortex, hippocampus, and basolateral amygdala of mouse brain

BACKGROUND

Pregnancy affects learning and memory in women. Thus, to investigate the effects of pregnancy, the authors examined the brain electrophysiology of pregnant mice.

METHODS

Using the whole-cell patch-clamp technique on isolated brain slices, we detected and compared the electrophysiological changes in the hippocampal CA1 (HIP CA1) region, medial prefrontal cortex (mPFC), and basolateral amygdala (BLA) among 15 pregnant and 15 nonpregnant mice.

RESULTS

In pregnant mice, there was a trend toward an increase in the frequency of miniature excitatory postsynaptic currents (mEPSCs) (p = 0.092) and a trend toward a decrease in the amplitude of miniature inhibitory postsynaptic currents (mIPSC) (p = 0.071) in the HIP CA1. In the BLA, both the amplitudes of mEPSCs and mIPSCs were significantly reduced (p = 0.004 and 0.042, respectively). In the mPFC, the amplitudes of mEPSCs and hyperpolarization-activated currents (Ih), as well as the frequencies of mIPSCs, were higher compared to nonpregnant mice (p = 0.035, 0.009, and 0.038, respectively).

CONCLUSIONS

In pregnant mice, the electrophysiological change in neurons in the mPFC and BLA might contribute to the cognitive and emotional changes during pregnancy. A trend toward electrophysiological change in the HIP CA1 revealed that the mechanism of cognitive change during pregnancy might differ from that of other conditions.

Effects of ketamine on fear memory extinction: a review of preclinical literature

Introduction

Ketamine, a multimodal dissociative anesthetic, is widely used as a trauma analgesic in emergency situations. Ketamine is also used to treat psychiatric disorders due to its broad application potential, including treatment-resistant major depression. However, its impacts on the development of post-traumatic stress disorder (PTSD) and its potential as a treatment for PTSD are controversial. PTSD is marked by persistent and intrusive memories of traumatic event(s) and re-experiencing of the traumatic memories when exposed to trauma-related stimuli. Individuals with PTSD are often treated with prolonged exposure therapy (PE), in which they are gradually exposed to stimuli that remind them of the previous traumatic memory. If successful, they may learn that the previously traumatic stimuli are no longer threatening, a process known as fear extinction. Although fear extinction can be studied in laboratory animals, previous preclinical literature on the effects of ketamine on fear extinction has been inconsistent.

Methods

Thus, we summarized the existing preclinical literature examining effects of ketamine on fear extinction and its potential molecular mechanisms.

Results

Studies found that ketamine may enhance, impair, have no effect, or have mixed effects on fear extinction. These discrepancies may be attributed to differences in dosage, route, and timing of ketamine administration.

Discussion

We conclude the review with recommendations for future research on ketamine and PTSD such as the inclusion of more female subjects, clinically relevant doses and routes of ketamine administration, and more comprehensive behavioral assays that are relevant to PTSD in humans to enhance translation between preclinical and clinical research.

Culture and Behaviour Management of Children in the Dental Clinic: A Scoping Review

Cultural norms, beliefs, and practices influence parental expectations, children's responses, and the acceptance of behaviour management techniques (BMTs) in paediatric dentistry. Despite this, the existing guidelines often adopt a standardized approach, overlooking critical cultural differences. This scoping review maps the links between culture and behaviour management strategies in paediatric dental settings. A scoping review following PRISMA guidelines was conducted across PubMed, Cochrane Library, Web of Science, Google Scholar, and hand-searched sources from the inception of the databases to 31 January 2025. A total of 671 studies were identified, with 15 meeting the inclusion criteria. Data on the key findings were inductively analyzed to assess cultural influences on parental acceptance, child behavior, and communication. The findings show that non-invasive BMTs such as TellShow-Do and positive reinforcement were the most accepted across cultures, while passive and active restraints were least accepted, especially in Western populations. Parental preferences varied; Jordanian parents were more accepting of passive restraint than German parents, while general anaesthesia was preferred in Bahrain. Cultural norms shaped communication styles-Latino families emphasized warm interpersonal interactions, whereas Pakistani families exhibited limited parental involvement due to language barriers. Black and Hispanic Medicaid-enrolled mothers in the U.S. reported lower satisfaction with pain management, highlighting disparities in culturally competent care. In conclusion, cultural factors significantly influence paediatric behaviour management in dental clinics. Integrating cultural competence into practice can enhance communication, improve patient compliance, and promote equitable care. Further research is needed, particularly in Africa and South America, to inform globally inclusive behaviour management guidelines.

Theta oscillations between the ventromedial prefrontal cortex and amygdala support dynamic representations of threat and safety

The amygdala exhibits distinct different activity patterns to threat and safety stimuli. Animal studies have demonstrated that the fear (i.e., threat) and extinction (i.e., safety) memory are encoded by the amygdala and its interaction with the ventromedial prefrontal cortex (vmPFC). Recent studies in both animals and humans suggest that the inter-regional interaction between amygdala and vmPFC can be supported by theta oscillations during fear processing. However, the mechanism by which the human vmPFC-amygdala pathway dynamically supports neural representations of the same stimulus remains elusive, as it alternatively reflects threat and safety situations. To investigate this phenomenon, we conducted intracranial EEG recordings in drug-resistant epilepsy patients (n = 8) with implanted depth electrodes who performed a fear conditioning and extinction task. This task was designed with a fixed structure whereby specific CS+ stimulus could be either safe (never paired with US) or threatening (possibly paired with US) based on an implicit rule during fear acquisition. Our findings showed that the stimulus embodying potential threat information was accompanied by increased theta activities in amygdala during both fear acquisition and early extinction. Furthermore, the learning of safety information was associated with enhanced theta-related direction from the vmPFC to the amygdala. This study provided directly electrophysiological evidence supporting the dynamic oscillatory modulation of threat and safety representations in the human amygdala-vmPFC circuit, and suggests that amygdala safety processing depends on theta inputs from the vmPFC in both fear acquisition and extinction.

Ready for translation: non-invasive auricular vagus nerve stimulation inhibits psychophysiological indices of stimulus-specific fear and facilitates responding to repeated exposure in phobic individuals

Recent laboratory research showed that vagus nerve stimulation promotes fear extinction, the inhibitory core mechanism of exposure treatment, presumably via activation of the noradrenergic brain system. However, a translation of this stimulation technique to clinical practice is lacking. We therefore investigated the potential of vagal stimulation to inhibit excessive fear responses and facilitate responding to in-vivo and laboratory exposure in individuals with specific phobia. Spider-phobic participants were subjected to three standardized in-vivo exposures towards a living tarantula, complemented by an exposure in vitro (between exposure in vivo I and II). Transcutaneous auricular vagus nerve stimulation (taVNS) was applied during in-vitro exposure, presenting pictures of the exposed tarantula, other spiders and neutral tools in the laboratory. Fear was assessed by self-reports and behavioral avoidance (in-vivo exposures), and amygdala-mediated autonomic and behavioral fear components (exposure in vitro). Vagal stimulation facilitated the reduction of behavioral avoidance across repeated in-vivo exposures. During laboratory exposure, taVNS inhibited fear tachycardia and corrugator muscle activity specifically in response to pictures of the previously exposed tarantula - an effect that became stronger with increasing stimulation duration. Psychophysiological indices of noradrenergic transmission in the basolateral amygdala were elevated during taVNS and correlated to subsequent attenuation of behavioral avoidance. Our results suggest, that taVNS exerts stimulus-specific and dose-dependent inhibition of multiple automatic response components of excessive fear, highlighting taVNS as a valuable adjunct to exposure-based treatment. A translational mechanism of action is supported, proposing that taVNS exhibits its effects by noradrenergic activation of fear extinction circuitry, particularly targeting the basolateral amygdala.

Changes in network centrality of anxiety and depression symptoms associated with childhood trauma among Chinese college students

BACKGROUND

Childhood trauma is strongly linked to anxiety and depression, significantly increasing the risk of negative outcomes in adulthood. This study employed network analysis to investigate the complex interplay of anxiety and depression symptoms among Chinese college students, focusing on identifying the core symptoms most directly affected by childhood trauma and those exerting the greatest influence on others.

METHODS

Data were collected from December 2020 to January 2021 from 2,266 college students at 16 institutions in southwestern and eastern coastal China. Depression, anxiety, and childhood trauma were assessed using the Patient Health Questionnaire-9, Generalized Anxiety Disorder-7, and Childhood Trauma Questionnaire-28, respectively. Separate symptom networks were constructed for participants with and without childhood trauma experiences. Central indices were employed to identify the central symptom within each network. The accuracy and stability of the networks were then evaluated. Finally, a network comparison test was used to analyze differences in network properties between the trauma and non-trauma groups.

RESULTS

Loss of Energy and Worry too much were the central symptoms in the non-trauma group, while anhedonia and nervousness were the central symptoms in the trauma group. There was a significant difference in the global strength of the network between the trauma group and the non-trauma group (pFDR< 0.01), but no significant difference in the distribution of edge weights between the two networks (pFDR =0.14). Anhedonia, Suicide ideation and Feeling afraid in the trauma group showed increased network centrality compared with the non-trauma group.

CONCLUSIONS

This study demonstrates the profound impact of childhood trauma on the central symptoms of anxiety and depression in college students. Further research is warranted to investigate the specific pathways through which these symptoms develop, with the goal of developing targeted interventions for this vulnerable population.

Fear conditioning: Insights into learning, memory and extinction and its relevance to clinical disorders

Fear, whether innate or learned, is an essential emotion required for survival. The learning, and subsequent memory, of fearful events enhances our ability to recognise and respond to threats, aiding adaptation to new, ever-changing environments. Considerable research has leveraged associative learning protocols such as contextual or auditory forms of fear conditioning in rodents, to understand fear learning, memory consolidation and extinction phases of memory. Such assays have led to detailed characterisation of the underlying neurocircuitry and neurobiology supporting fear learning processes. Given fear processing is conserved across rodents and humans, fear conditioning experiments provide translational insights into fundamental memory processes and fear-related pathologies. This review examines associative learning protocols used to measure fear learning, memory and extinction, before providing an overview on the underlying complex neurocircuitry including the amygdala, hippocampus and medial prefrontal cortex. This is followed by an in-depth commentary on the neurobiology, particularly synaptic plasticity mechanisms, which regulate fear learning, memory and extinction. Next, we consider how fear conditioning assays in rodents can inform our understanding of disrupted fear memory in human disorders such as post-traumatic stress disorder (PTSD), anxiety and psychiatric disorders including schizophrenia. Lastly, we critically evaluate fear conditioning protocols, highlighting some of the experimental and theoretical limitations and the considerations required when conducting such assays, alongside recent methodological advancements in the field. Overall, rodent-based fear conditioning assays remain central to making progress in uncovering fundamental memory phenomena and understanding the aetiological mechanisms that underpin fear associated disorders, alongside the development of effective therapeutic strategies.

Infralimbic parvalbumin neural activity facilitates cued threat avoidance

The infralimbic cortex (IL) is essential for flexible behavioral responses to threatening environmental events. Reactive behaviors such as freezing or flight are adaptive in some contexts, but in others a strategic avoidance behavior may be more advantageous. IL has been implicated in avoidance, but the contribution of distinct IL neural subtypes with differing molecular identities and wiring patterns is poorly understood. Here, we study IL parvalbumin (PV) interneurons in mice as they engage in active avoidance behavior, a behavior in which mice must suppress freezing in order to move to safety. We find that activity in inhibitory PV neurons increases during movement to avoid the shock in this behavioral paradigm, and that PV activity during movement emerges after mice have experienced a single shock, prior to learning avoidance. PV neural activity does not change during movement toward cued rewards or during general locomotion in the open field, behavioral paradigms where freezing does not need to be suppressed to enable movement. Optogenetic suppression of PV neurons increases the duration of freezing and delays the onset of avoidance behavior, but does not affect movement toward rewards or general locomotion. These data provide evidence that IL PV neurons support strategic avoidance behavior by suppressing freezing.

Dopamine in the tail of the striatum facilitates avoidance in threat-reward conflicts

Responding appropriately to potential threats before they materialize is critical to avoiding disastrous outcomes. Here we examine how threat-coping behavior is regulated by the tail of the striatum (TS) and its dopamine input. Mice were presented with a potential threat (a moving object) while pursuing rewards. Initially, the mice failed to obtain rewards but gradually improved in later trials. We found that dopamine in TS promoted avoidance of the threat, even at the expense of reward acquisition. Furthermore, the activity of dopamine D1 receptor-expressing neurons promoted threat avoidance and prediction. In contrast, D2 neurons suppressed threat avoidance and facilitated overcoming the potential threat. Dopamine axon activation in TS not only potentiated the responses of dopamine D1 receptor-expressing neurons to novel sensory stimuli but also boosted them acutely. These results demonstrate that an opponent interaction of D1 and D2 neurons in the TS, modulated by dopamine, dynamically regulates avoidance and overcoming potential threats.

Dopamine modulation of basolateral amygdala activity and function

The basolateral amygdala (BLA) is central to emotional processing, fear learning, and memory. Dopamine (DA) significantly influences BLA function, yet its precise effects are not clear. We present a mathematical model exploring how DA modulation of BLA activity depends on the network's current state. Specifically, we model the firing rates of interconnected neural groups in the BLA and their responses to external stimuli and DA modulation. BLA projection neurons are separated into two groups according to their responses-fear and safety. These groups are connected by mutual inhibition though interneurons. We contrast 'differentiated' BLA states, where fear and safety projection neurons exhibit distinct activity levels, with 'non-differentiated' states. We posit that differentiated states support selective responses and short-term emotional memory. On the other hand, non-differentiated states represent either the case in which BLA is disengaged, or the activation of the fear and safety neurons is at a similar moderate or high level. We show that, while DA further disengages BLA in the low activity state, it destabilizes the moderate activity non-differentiated BLA state. We show that in the latter non-differentiated state the BLA is hypersensitive, and the polarity of its responses (fear or safety) to salient stimuli is highly random. We hypothesize that this non-differentiated state is related to anxiety and Post-Traumatic Stress Disorder (PTSD).

The Effect of Suvorexant on Fear Extinction Recall: A Double-Blind Randomised Controlled Pilot Trial in Healthy Individuals

Post-traumatic stress disorder (PTSD) is a highly debilitating condition that develops after trauma exposure. Dysregulation in extinction memory consolidation (i.e., the ability to remember that trauma-related stimuli no longer signal danger) is proposed to underlie PTSD development. Disruptions in rapid eye movement (REM) sleep are thought to be the key contributor to this dysregulation, as REM sleep is suggested to play a vital role in the processing of emotional memories. While previous literature has investigated the role of natural REM sleep variations or REM sleep disruptions on extinction recall capacities, none have attempted to increase REM sleep to improve extinction recall. In this pilot, randomised controlled trial, we investigated the effect of 20 mg suvorexant to increase REM sleep, 20 mg temazepam to decrease REM sleep, and a placebo on extinction recall in 30 healthy adults (age: M = 26.93 years, SD = 7.54). Overall, no difference in REM percentage (p = 0.68, η2 = 0.0.03, small effect), nor in extinction recall (p = 0.58, η2 = 0.04, small effect) was observed between the drug conditions. However, increased REM percentage was associated with decreased conditioned fear response at recall, indicating better extinction recall (β = -0.71, p = 0.03, ηp 2 = 0.10; moderate effect) across the sample. These findings suggest that increasing REM sleep in populations with REM disruptions such as PTSD to optimal levels could improve extinction recall. This underscores the potential of enhancing REM sleep as a therapeutic target for improving PTSD outcomes, warranting further investigation of suvorexant in clinical populations where REM sleep deficits are prevalent.

Person-centered analyses reveal that developmental adversity at moderate levels and neural threat/safety discrimination are associated with lower anxiety in early adulthood

Parsing heterogeneity in the nature of adversity exposure and neurobiological functioning may facilitate better understanding of how adversity shapes individual variation in risk for and resilience against anxiety. One putative mechanism linking adversity exposure with anxiety is disrupted threat and safety learning. Here, we applied a person-centered approach (latent profile analysis) to characterize patterns of adversity exposure at specific developmental stages and threat/safety discrimination in corticolimbic circuitry in 120 young adults. We then compared how the resultant profiles differed in anxiety symptoms. Three latent profiles emerged: (1) a group with lower lifetime adversity, higher neural activation to threat, and lower neural activation to safety; (2) a group with moderate adversity during middle childhood and adolescence, lower neural activation to threat, and higher neural activation to safety; and (3) a group with higher lifetime adversity exposure and minimal neural activation to both threat and safety. Individuals in the second profile had lower anxiety than the other profiles. These findings demonstrate how variability in within-person combinations of adversity exposure and neural threat/safety discrimination can differentially relate to anxiety, and suggest that for some individuals, moderate adversity exposure during middle childhood and adolescence could be associated with processes that foster resilience to future anxiety.

The impact of distal stress on the spontaneous recovery of conditioned defensive responses

Intense and chronic stress strengthens fear memories and increases the risk for mental disorders. Often stressful situations are experienced long before the appearance of the symptoms, but so far, little has been investigated on how distal stress alters fear memories. In a four-day paradigm, 131 healthy individuals were either assigned to the stress-group by means of the socially evaluated cold-pressor test (SECPT) or to the sham-group (control condition). Twenty-four hours later, participants underwent fear acquisition during which two shapes were presented. The first shape (conditioned stimulus, CS+) was associated with an electro-tactile stimulation (unconditioned stimulus, US), whereas the second shape (CS-) were presented alone. During extinction training, both shapes were presented while the US was omitted. To investigate if stress induction alters extinction recall differently depending on the passage of time, participants were tested either one day (recent) or 15 days (remote) after extinction training. Learning was quantified via subjective ratings, startle reflex and skin conductance response. While we found successful acquisition and extinction of the conditioned defensive responses, there was no effect of stress on these learning processes. Stress induction did not alter the spontaneous recovery of the conditioned defensive verbal responses but of the physiological responses as stressed individuals tested two weeks after extinction training showed startle potentiation to CS + vs. CS-. In conclusion, distal stress, even if mild, can strengthen fear memories and weaken extinction memory by the passage of time. This could be a possible mechanism facilitating the onset of stress-related and anxiety disorders.

Intermittent theta burst stimulation to the left prefrontal cortex enhances extinction learning but not extinction recall

BACKGROUND

Non-invasive brain stimulation targeting the left ventromedial prefrontal cortex (vmPFC) has shown potential in enhancing fear extinction. However, optimal stimulation parameters for clinical application remain unclear.

METHODS

This study investigated the effects of intermittent theta burst stimulation (iTBS) on fear extinction using a three-day paradigm. Fifty healthy participants underwent fear acquisition (day 1), extinction learning (day 2), and both a spontaneous recovery and reinstatement test (day 3). Active or sham iTBS was applied before extinction learning to the left posterior PFC (MNI: -56, 2, 40), previously shown to be functionally connected to the vmPFC. Fear responses were measured using skin conductance responses (SCR) during CS+ and CS- presentations, along with arousal, valence, and contingency awareness ratings.

RESULTS

A significant time x group interaction was found for iTBS administered before extinction learning, with the active group showing reduced SCR during extinction learning compared to sham. However, no TMS effects were observed during the spontaneous recovery or reinstatement tests.

CONCLUSION

These findings suggest limited therapeutic potential for iTBS targeting the left posterior PFC in enhancing extinction memory consolidation. Further research is needed to determine optimal stimulation parameters for clinical application.

Chlorpyrifos intermittent exposure enhances cardiovascular but not behavioural responses to contextual fear conditioning in adult rats: Possible involvement of brain oxidative-nitrosative stress

Exposure to organophosphorus compounds (OPs) may cause psychiatric, neurologic, biochemical, and cardiovascular abnormalities. Neurotoxicity of OP compounds is primarily due to irreversibly inhibition of the acetylcholinesterase (AChE) enzyme both centrally and peripherally. Chlorpyrifos (CPF) is a widely used OP classified as moderately toxic. Previously, it has been shown that CPF administration, given every other day to adult rats, impairs spatial memory and prepulse inhibition associated with brain AChE inhibition. Our group also found that intermittent treatment with CPF, simulating occupational exposure, impairs the cardiorespiratory reflexes and causes cardiac hypertrophy. Thereby, we aimed to examine whether subchronic and intermittent administration of CPF would affect the behavioural (freezing) and cardiovascular (mean arterial pressure, MAP; heart rate, HR) responses elicited during contextual fear conditioning (CFC) and extinction. Wistar adult male rats were injected with sublethal and intermittent CPF doses (4 and 7 mg/kg) three times a week for one month. Two days after the last injection, a range of tests were performed to assess depression (sucrose preference), anxiety (elevated plus-maze, EPM), locomotion (open field, OF), and conditioned fear expression and extinction. Separate cohorts of animals were euthanized to measure plasma butyrylcholinesterase (BChE), erythrocyte AChE, brain AChE activity, and markers of oxidative-nitrosative stress. Intermittent CPF treatment did not affect sucrose preference. CPF (4 and 7 mg/kg) reduced open-arms exploration in the EPM, suggesting an anxiogenic effect. The higher dose of CPF decreased the total distance travelled in the OFT, suggesting motor impairment. After a seven-day CPF-free washout period, CPF (7 mg/kg) increased the tachycardic response without affecting freezing behaviour in the CFC extinction session. CPF 7 mg/kg decreased AChE activity in the hippocampus, pre-frontal cortex and brainstem 72 after the last administration whilst transiently increasing oxidative-nitrosative stress specifically in the brainstem. Overall, our results outlined the behavioural, autonomic and biochemical abnormalities caused by an intermittent dosing regimen of CPF that elicits brain AChE inhibition and brain oxidative-nitrosative stress. This paradigm might be valuable in further exploring long-term consequences and mechanisms of OP neurotoxicity as well as comprehensive therapeutic approaches.

Building Resilience: The Stress Response as a Driving Force for Neuroplasticity and Adaptation

People exhibit an extraordinary capacity to adjust to stressful situations. Here, we argue that the acute stress response is a major driving force behind this adaptive process. In addition to immediately freeing energy reserves, facilitating a rapid and robust neurocognitive response, and helping to reinstate homeostasis, the stress response also critically regulates neuroplasticity. Therefore, understanding the healthy acute stress response is crucial for understanding stress resilience-the maintenance or rapid recovery of mental health during and after times of adversity. Contemporary resilience research differentiates between resilience factors and resilience mechanisms. Resilience factors refer to a broad array of social, psychological, or biological variables that are stable but potentially malleable and predict resilient outcomes. In contrast, resilience mechanisms refer to proximate mechanisms activated during acute stress that enable individuals to effectively navigate immediate challenges. In this article, we review literature related to how neurotransmitter and hormonal changes during acute stress regulate the activation of resilience mechanisms. We integrate literature on the timing-dependent and neuromodulator-specific regulation of neurocognition, episodic memory, and behavioral and motivational control, highlighting the distinct and often synergistic roles of catecholamines (dopamine and norepinephrine) and glucocorticoids. We conclude that stress resilience is bolstered by improved future predictions and the success-based reinforcement of effective coping strategies during acute stress. The resulting generalized memories of success, controllability, and safety constitute beneficial plasticity that lastingly improves self-control under stress. Insight into such mechanisms of resilience is critical for the development of novel interventions focused on prevention rather than treatment of stress-related disorders.

Treatment Approaches for Posttraumatic Stress Disorder Derived From Basic Research on Fear Extinction

This brief review article will describe treatment approaches for posttraumatic stress disorder (PTSD) based on findings from basic research. The focus of this review will be fear conditioning and extinction models, which provide a translational model of PTSD that can help translate basic research in nonhuman animals through well-controlled trials confirming the efficacy of treatment approaches in humans with PTSD such as prolonged exposure therapy. Specific cognitive aspects of fear extinction processes, including consolidation and reconsolidation, are reviewed along with behavioral and pharmacological treatment strategies based on basic research in these areas including attempts to prevent the development of PTSD as well as the treatment of chronic PTSD. Pharmacological, behavioral, and device-based augmentation strategies of PTSD treatment based in basic science findings are reviewed, including those that disrupt noradrenergic receptor processes, medications that act on NMDA receptors, physical exercise, cannabinoids, estradiol, dexamethasone, yohimbine, losartan, dopamine, and MDMA, along with the evidence for their efficacy in human clinical samples. While fear extinction provides an exciting translational opportunity to improve PTSD based on basic science findings, we review limitations and challenges of the extant literature as well as future directions.

Effects of intranasal oxytocin on fear extinction learning

Once a threat no longer exists, extinction of conditioned fear becomes adaptive in order to reduce allotted resources towards cues that no longer predict the threat. In anxiety and stress disorders, fear extinction learning may be affected. Animal findings suggest that the administration of oxytocin (OT) modulates extinction learning in a timepoint-dependent manner, facilitating extinction when administered prior to fear conditioning, but impairing it when administered prior to extinction learning. The aim of the present study was to examine if these findings translate into human research. Using a randomized, double-blind, placebo-controlled, 2-day fear conditioning and extinction learning design, behavioral (self-reported anxiety), physiological (skin conductance response), neuronal (task-based and resting-state functional magnetic resonance imaging), and hormonal (cortisol) data were collected from 124 naturally cycling (taking no hormonal contraceptives) healthy females. When administered prior to conditioning (Day 1), OT, similar to rodent findings, did not affect fear conditioning, but modulated the intrinsic functional connectivity of the anterior insula immediately after fear conditioning. In contrast to animal findings, OT impaired, not facilitated, extinction learning on the next day and increased anterior insula activity. When administered prior to extinction learning (day 2), OT increased the activity in the bilateral middle temporal gyrus, and similar to animal findings, reduced extinction learning. The current findings suggest that intranasal OT impedes fear extinction learning in humans regardless of the timepoint of administration, providing new insights and directions for future translational research and clinical applications.

Modulation of Fear Extinction by Non-Invasive Brain Stimulation: Systematic Review and Meta-Analysis

Non-invasive brain stimulation (NIBS) is an emerging treatment for mental disorders that is painlessness and easy to administer. However, its effectiveness for modulating fear extinction requires further elucidation. We searched eight bibliographical databases and identified randomized controlled trials of NIBS and fear extinction in healthy populations. Outcomes were evaluated based on skin conductance responses (SCRs) under three experimental stimuli: threat condition stimulation (CS+), safe condition stimulation (CS-), and their discrimination (CS+ minus CS-). We applied a random-effects model to determine effect sizes (Hedge's g) post-stimulation and assessed article quality using Physiotherapy evidence database (PEDro) scale. Twenty-one studies meeting systematic review criteria were included in this analysis, incorporating 40 independent effect sizes and data from 11 studies (n = 632) in the meta-analysis. Compared with the control group, SCRs in CS+ and discrimination were significantly reducted in the intervention group. Fear extinction was more effective in the 24-h test than immediately after NIBS. In conclusion, NIBS enhanced fear extinction, and the time interval between stimulation and testing may serve as a moderating variable.

Fear and safety learning in anxiety- and stress-related disorders: An updated meta-analysis

Fear learning processes are believed to play a crucial role in the development and maintenance of anxiety and stress-related disorders. To integrate results across different studies, we conducted a systematic meta-analysis following PRISMA guidelines to examine differences in fear conditioning during fear acquisition, extinction, and extinction recall between individuals with anxiety-related or stress-related disorders and healthy participants. This analysis updates the work of Duits et al. (2015) while also refining distinctions between physiological and behavioral outcomes and examining extinction recall. Our meta-analysis encompasses 77 studies published from 1986 to 2022, involving 2052 patients with anxiety disorders, obsessive-compulsive disorder, or post-traumatic stress disorder, and 3258 healthy controls. The results indicate significant differences in fear acquisition, extinction, and recall between the two groups. Specifically, during acquisition patients exhibited heightened physiological and behavioral responses to the CS- and reported increased affect ratings for the CS+ . During extinction and extinction recall, patients continue to show heightened threat expectancy and negative affect ratings towards the CS- and increased affect ratings towards the CS+ . No differences were found in CS+ /CS- differentiation between groups. These findings imply that individuals with anxiety and stress-related disorders may exhibit amplified responses to safety cues and stronger reactions to threat cues during fear conditioning, lasting through extinction and extinction recall. These changes may lead to increased sensitivity in detecting fear and slower extinction process, resulting in more enduring anxiety responses. We discuss these results in the context of existing literature on fear and safety learning and consider potential underlying mechanisms.

The impact of exercise interventions on sleep in adult populations with depression, anxiety, or posttraumatic stress: review of the current evidence and future directions

Consistent evidence suggests that exercise leads to improvements in subjective sleep quality and also objective sleep metrics in non-psychiatric adult populations. However, the degree to which exercise provides sleep benefits for adults with psychiatric disorders is less known, despite the potential benefits given that sleep disturbance is prevalent in these populations. In this narrative review, we synthesize results of randomized controlled trials examining the influence of aerobic and/or resistance exercise interventions on sleep outcomes in adult psychiatric populations. We specifically focus on populations with elevated symptoms or diagnoses of depression, anxiety, or posttraumatic stress disorder. A systematic search through June 2024 yielded 26 relevant trials. Overall, most trials reported improvement of subjective sleep quality after aerobic and/or resistance exercise programs in samples with depression. Similar effects were observed for posttraumatic stress; however, larger trials are needed. Further research is needed to examine the impact of exercise on sleep in anxiety populations as only one trial with mixed results was identified. Results were more equivocal for the subpopulation of adult women with perinatal or postpartum depression, demonstrating the importance of understanding exercise effects on sleep in specific subpopulations. Few studies examined objective sleep outcomes, impact of acute exercise on next day sleep, or the interplay between exercise, sleep, and psychiatric symptom changes, all important areas of future research. Other implications and future directions are discussed, including potential moderators and mechanisms of action that warrant further study to better understand how exercise interventions may optimally target sleep in psychiatric populations.

Slow oscillation-sleep spindle coupling is associated with fear extinction retention in trauma-exposed individuals

Posttraumatic stress disorder (PTSD) can be characterized as a disorder of fear learning and memory, in which there is a failure to retain memory for the extinction of conditioned fear. Sleep has been implicated in successful extinction retention. The coupling of sleep spindles to slow oscillations (SOs) during non-rapid eye movement sleep has been shown to broadly underpin sleep's beneficial effect on memory consolidation. However, the role of this oscillatory coupling in the retention of extinction memories is unknown. In a large sample of 124 trauma-exposed individuals, we investigated SO-spindle coupling in relation to fear extinction memory. We found that participants with a PTSD diagnosis, relative to trauma-exposed controls, showed significantly altered SO-spindle timing, such that PTSD participants exhibited spindle coupling further away from the peak of the SO. Across participants, the amount of coupling significantly predicted extinction retention, with coupled spindles uniquely predicting successful extinction retention compared to uncoupled spindles. These results suggest that SO-spindle coupling is critical for successful retention of extinguished fear, and that SO-spindle coupling dynamics are altered in PTSD. These alterations in the mechanics of sleep may have substantial clinical implications, meriting further investigation.

Transcranial magnetic stimulation for obsessive-compulsive disorder and post-traumatic stress disorder: A comprehensive systematic review and analysis of therapeutic benefits, cortical targets, and psychopathophysiological mechanisms

Transcranial magnetic stimulation (TMS) is a safe non-invasive treatment technique. We systematically reviewed randomised controlled trials (RCTs) applying TMS in obsessive compulsive disorder (OCD) and post-traumatic stress disorder (PTSD) to analyse its therapeutic benefits and explore the relationship between cortical target and psychopathophysiology. We included 47 randomised controlled trials (35 for OCD) and found a 22.7 % symptom improvement for OCD and 29.4 % for PTSD. Eight cortical targets were investigated for OCD and four for PTSD, yielding similar results. Bilateral dlPFC-TMS exhibited the greatest symptom change (32.3 % for OCD, N = 4 studies; 35.7 % for PTSD, N = 1 studies), followed by right dlPFC-TMS (24.4 % for OCD, N = 8; 26.7 % for PTSD, N = 10), and left dlPFC-TMS (22.9 % for OCD, N = 6; 23.1 % for PTSD, N = 1). mPFC-TMS showed promising results, although evidence is limited (N = 2 studies each for OCD and PTSD) and findings for PTSD were conflicting. Despite clinical improvement, reviewed reports lacked a consistent and solid rationale for cortical target selection, revealing a gap in TMS research that complicates the interpretation of findings and hinders TMS development and optimisation. Future research should adopt a hypothesis-driven approach rather than relying solely on correlations from imaging studies, integrating neurobiological processes with affective, behavioural, and cognitive states, thereby doing justice to the complexity of human experience and mental illness.

The power of belief? Evidence of reduced fear extinction learning in Catholic God believers

Religious beliefs can shape how people process fear. Yet the psychophysiological mechanisms underlying this phenomenon remain poorly understood. We investigated fear learning and extinction processes in a group of individuals who professed a belief in God, compared to non-believers. Using a virtual reality Pavlovian fear conditioning/extinction task, we measured neurovegetative activity associated with these forms of associative learning. Our finding shows reduced fear extinction among God believers, compared to non-believers. This suggests that the general mechanism of fear extinction learning is suppressed in these individuals. Importantly, this effect was not explained by state or trait anxiety scores. These findings align with previous evidence linking religiosity and spirituality with the neural circuit of fear and suggest that religiosity may be associated with weaker inhibitory learning processes related to fear.

Current State of the Neuroscience of Fear Extinction and Its Relevance to Anxiety Disorders

The elucidation of the functional neuroanatomy of human fear, or threat, extinction has started in the 2000s by a series of enthusiastically greeted functional magnetic resonance imaging (fMRI) studies that were able to translate findings from rodent research about an involvement of the ventromedial prefrontal cortex (vmPFC) and the hippocampus in fear extinction into human models. Enthusiasm has been painfully dampened by a meta-analysis of human fMRI studies by Fullana and colleagues in 2018 who showed that activation in these areas is inconsistent, sending shock waves through the extinction research community. The present review guides readers from the field (as well as non-specialist readers desiring safe knowledge about human extinction mechanisms) during a series of exposures with corrective information. New information about extinction-related brain activation not considered by Fullana et al. will also be presented. After completion of this exposure-based fear reduction program, readers will trust that the reward learning system, the cerebellum, the vmPFC, the hippocampus, and a wider brain network are involved in human fear extinction, along with the neurotransmitters dopamine and noradrenaline. Specific elements of our exposure program include exploitation of the temporal dynamics of extinction, of the spatial heterogeneity of extinction-related brain activation, of functional connectivity methods, and of large sample sizes. Implications of insights from studies in healthy humans for the understanding and treatment of anxiety-related disorders are discussed.

Efficacy of fluoxetine and (R,S)-ketamine in attenuating conditioned fear behaviors in male mice

Post-traumatic stress disorder (PTSD) is caused by exposure to a traumatic or stressful event. Symptoms related to this disorder include persistent re-experiencing of memories and fear of generalization. Current pharmacological treatments for PTSD are insufficient, with fewer than 30% of patients reporting symptom remission. This study aims to determine the efficacy of acute (R,S)-ketamine and chronic fluoxetine (FLX) in reducing fear memory and fear generalization. In rodents, fear conditioning (FC) is commonly used in the literature to induce behaviors related to symptoms of PTSD, and the open field test (OFT) can assess anxiety and fear generalization behaviors during the exploration of a novel environment. In this study, FC consisted of a white noise cue stimulus and 4 inescapable foot shocks. Treatments began 4 hours after FC. Fear and anxiety behaviors were recorded during re-exposure to the FC stimuli at 24 hours and 2 weeks. The OFT was conducted 1 day before the last FC re-exposure. Results support the combined use of acute ketamine and chronic FLX as a treatment for reducing behaviors indicative of fear memory during re-exposure at 2 weeks, but not behaviors indicative of anxiety and fear generalization in the OFT. FLX alone was most effective in reducing behaviors related to fear generalization. This study contributes to the existing literature on pharmacological treatment for fear and anxiety behaviors relating to fear memory and fear generalization. Continued research is necessary to replicate results, optimize treatment protocols, and investigate the molecular adaptations to trauma and treatment. SIGNIFICANCE STATEMENT: Up to 6% of people in the United States will develop PTSD within their lifetime, and less than half of those individuals will find relief from their symptoms given the current therapeutic options. This study offers preliminary support for the efficacy of ketamine and FLX in reducing PTSD-like behaviors induced by fear-conditioning in mice. Compared with current standard treatments, the results of the current study indicate the potential for a more effective therapeutic option for those with stress-related disorders, such as PTSD.

Fear extinction retention in children, adolescents, and adults

Past results suggest that fear extinction and the return of extinguished fear are compromised in adolescents. However, findings have been inconclusive as there is a lack of fear extinction and extinction retention studies including children, adolescents and adults. In the present study, 36 children (6-9 years), 40 adolescents (13-17 years) and 44 adults (30-40 years), underwent a two-day fear conditioning task. Habituation, acquisition, and extinction were performed on the first day and an extinction retention test > 24 h later. Skin conductance responses were recorded during all phases of fear conditioning and functional magnetic resonance imaging (fMRI) was conducted during the fear retention test. All groups acquired and extinguished fear as measured with SCR, with no group differences in SCR during extinction retention. The groups had largely similar neural fear responses during the retention test, apart from adolescents displaying stronger amygdala fear response than children, with no differences between adolescents and adults. The findings do not support an adolescent extinction dip, and there was only marginal evidence of progressive changes in fear conditioning across development. In contrast to findings in rodents, fear conditioning in humans may elicit similar physiological responses and recruit similar neural networks from childhood to adulthood.

Emotion Regulation Under Stress: A Social Processing and Memory Perspective

Research on emotion regulation often focuses on cognitively effortful self-regulation strategies, but exposure to stress has been shown to interfere with the underlying mechanisms supporting such processes. Understanding alternative strategies that potentially bolster emotion regulation under stress is an important topic of investigation. Two potential alternatives involve everyday occurrences of social processing and memory recall. Social support and past emotional experiences may help in guiding us toward appropriate neurophysiological responses through overlapping circuitry with stress and reward systems, while also buttressing cognitive regulation strategies by expanding one's perspective and allowing multiple opportunities to regulate retrospectively. In recognition that ongoing social and emotional events are often at the beginning of a cascade of both emotion regulation and memory processes, this chapter focuses on the emerging role of social relationships and autobiographical memory recall in regulating emotions under stress, highlighting opportunities and challenges associated with this process.

Meta-analytic connectivity perturbation analysis (MACPA): a new method for enhanced precision in fMRI connectivity analysis

Co-activation of distinct brain areas provides a valuable measure of functional interaction, or connectivity, between them. One well-validated way to investigate the co-activation patterns of a precise area is meta-analytic connectivity modeling (MACM), which performs a seed-based meta-analysis on task-based functional magnetic resonance imaging (task-fMRI) data. While MACM stands as a powerful automated tool for constructing robust models of whole-brain human functional connectivity, its inherent limitation lies in its inability to capture the distinct interrelationships among multiple brain regions. Consequently, the connectivity patterns highlighted through MACM capture the direct relationship of the seed region with third brain regions, but also a (less informative) residual relationship between the third regions themselves. As a consequence of this, this technique does not allow to evaluate to what extent the observed connectivity pattern is really associated with the fact that the seed region is activated, or it just reflects spurious co-activations unrelated with it. In order to overcome this methodological gap, we introduce a meta-analytic Bayesian-based method, called meta-analytic connectivity perturbation analysis (MACPA), that allows to identify the unique contribution of a seed region in shaping whole-brain connectivity. We validate our method by analyzing one of the most complex and dynamic structures of the human brain, the amygdala, indicating that MACPA may be especially useful for delineating region-wise co-activation networks.

C5aR1 inhibition alleviates cranial radiation-induced cognitive decline

Cranial radiation therapy (RT) for brain cancers leads to an irreversible decline in cognitive function without an available remedy. Radiation-induced cognitive deficits (RICD) are a particularly pressing problem for the survivors of pediatric and low grade glioma (LGG) cancers who often live long post-RT lives. Radiation-induced elevated neuroinflammation and gliosis, triggered by the detrimental CNS complement cascade, lead to excessive synaptic and cognitive loss. Using intact and brain cancer-bearing mouse models, we now show that targeting anaphylatoxin complement C5a receptor (C5aR1) is neuroprotective against RICD. We used a genetic knockout, C5aR1 KO mouse, and a pharmacologic approach, employing the orally active, brain penetrant C5aR1 antagonist PMX205 to reverse RICD. Irradiated C5aR1 KO and WT mice receiving PMX205 showed significant neurocognitive improvements in object recognition memory and memory consolidation tasks. Inhibiting C5a/C5aR1 axis reduced microglial activation, astrogliosis, and synaptic loss in the irradiated brain. Importantly, C5aR1 blockage in two syngeneic, orthotopic glioblastoma-bearing mice protected against RICD without interfering with the therapeutic efficacy of RT to reduce tumor volume in vivo . PMX205 clinical trials with healthy individuals and amyotrophic lateral sclerosis (ALS) patients showed no toxicity, drug-related adverse events, or infections. Thus, C5aR1 inhibition is a translationally feasible approach to address RICD, an unmet medical need.

SIGNIFICANCE

Cranial radiotherapy for brain cancers activates CNS complement cascade, leading to cognitive decline. Ablation of the complement C5a/C5aR1 axis alleviates radiation-induced neuroinflammation, synaptic loss, and cognitive dysfunction, providing a novel tractable approach.

P2X7 receptors modulate acquisition of cue fear extinction and contextual background memory generalization in male mice

The purinergic P2X7 receptors (P2X7R) are activated by adenosine triphosphate (ATP) in several brain regions, particularly those involved with emotional control and the regulation of fear-related memories. Here, we investigate the role of P2X7R in fear learning memory, specifically in the acquisition and consolidation phases of the cued fear conditioning paradigm. C57Bl/6 wildtype (WT) male mice that received a single i.p. injection of the selective P2X7R antagonist A438079 prior the conditioning session showed generalization of cued fear memory and impaired fear extinction recall in the test session, while those treated prior the extinction session exhibited a similar behavior profile accompanied by resistance in the extinction learning. However, no effects were observed when this drug was administered immediately after the conditioning, extinction, or before the test session. Our results with P2X7R knockout (P2X7 KO) mice showed a behavioral profile that mirrored the collective effects observed across all pharmacological treatment conditions. This suggests that the P2X7R KO model effectively replicates the behavioral changes induced by the pharmacological interventions, demonstrating that we have successfully isolated the role of P2X7R in the fear and extinction phases of memory. These findings highlight the role of P2X7R in the acquisition and recall of extinction memory and supports P2X7R as a promising candidate for controlling abnormal fear processing, with potential applications for stress exposure-related disorders such as post-traumatic stress disorder (PTSD).

REM disruption and REM vagal activity predict extinction recall in trauma-exposed individuals

BACKGROUND

Accumulating evidence suggests that rapid eye movement sleep (REM) supports the consolidation of extinction memory. REM is disrupted in posttraumatic stress disorder (PTSD), and REM abnormalities after traumatic events increase the risk of developing PTSD. Therefore, it was hypothesized that abnormal REM in trauma-exposed individuals may pave the way for PTSD by interfering with the processing of extinction memory. In addition, PTSD patients display reduced vagal activity. Vagal activity contributes to the strengthening of memories, including fear extinction memory, and recent studies show that the role of vagus in memory processing extends to memory consolidation during sleep. Therefore, it is plausible that reduced vagal activity during sleep in trauma-exposed individuals may be an additional mechanism that impairs extinction memory consolidation. However, to date, the contribution of sleep vagal activity to the consolidation of extinction memory or any emotional memory has not been investigated.

METHODS

Trauma-exposed individuals (n = 113) underwent a 2-day fear conditioning and extinction protocol. Conditioning and extinction learning phases were followed by extinction recall 24 h later. The association of extinction recall with REM characteristics and REM vagal activity (indexed as heart rate variability) during the intervening consolidation night was examined.

RESULTS

Consistent with our hypotheses, REM disruption was associated with poorer physiological and explicit extinction memory. Furthermore, higher vagal activity during REM was associated with better explicit extinction memory, and physiological extinction memory in males.

CONCLUSIONS

These findings support the notion that abnormal REM, including reduced REM vagal activity, may contribute to PTSD by impairing the consolidation of extinction memory.

Handholding reduces the recovery of threat memories and magnifies prefrontal hemodynamic responses

Human touch is a powerful means of social and affective regulation, promoting safety behaviors. Yet, despite its importance across human contexts, it remains unknown how touch can promote the learning of new safety memories and what neural processes underlie such effects. The current study used measures of peripheral physiology and brain activity to examine the effects of interpersonal touch during safety learning (extinction) on the recovery of previously learned threat. We observed that handholding during extinction significantly reduced threat recovery, which was reflected in enhanced prefrontal hemodynamic responses. This effect was absent when learners were instructed to hold a rubber ball, independent of the presence of their partners. Our findings indicate that social touch contributes to safety learning, potentially influencing threat memories via prefrontal circuitry.

The unique face of comorbid anxiety and depression: Increased frontal, insula and cingulate cortex response during Pavlovian fear-conditioning

BACKGROUND

Dysregulation of fear processing through altered sensitivity to threat is thought to contribute to the development of anxiety disorders and major depressive disorder (MDD). However, fewer studies have examined fear processing in MDD than in anxiety disorders. The current study used propensity matching to examine the hypothesis that comorbid MDD and anxiety (AnxMDD) shows greater neural correlates of fear processing than MDD, suggesting that the co-occurrence of AnxMDD is exemplified by exaggerated defense related processes.

METHODS

195 individuals with MDD (N = 65) or AnxMDD (N = 130) were recruited from the community and completed multi-level assessments, including a Pavlovian fear learning task during functional imaging. Visual images paired with threat (conditioned stimuli: CS+) were compared to stimuli not paired with threat (CS-).

RESULTS

MDD and AnxMDD showed significantly different patterns of activation for CS+ vs CS- in the dorsal anterior insula/inferior frontal gyrus (partial eta squared; ηp2 = 0.02), dorsolateral prefrontal cortex (ηp2 = 0.01) and dorsal anterior/mid cingulate cortex (ηp2 = 0.01). These differences were driven by greater activation to the CS+ in AnxMDD versus MDD.

LIMITATIONS

Limitations include the cross-sectional design, a scream US rather than shock and half the number of MDD as AnxMDD participants.

CONCLUSIONS

AnxMDD showed a pattern of increased activation in regions identified with fear processing. Effects were consistently driven by threat, further suggesting fear signaling as the emergent target process. Differences emerged in regions associated with salience processing, attentional orienting/conflict, self-relevant processing and executive functioning in comorbid anxiety and depression, thereby highlighting potential treatment targets for this prevalent and treatment resistant group.

Neuropsychobiology of fear-induced bradycardia in humans: progress and pitfalls

In the last century, the paradigm of fear conditioning has greatly evolved in a variety of scientific fields. The techniques, protocols, and analysis methods now most used have undergone a progressive development, theoretical and technological, improving the quality of scientific productions. Fear-induced bradycardia is among these techniques and represents the temporary deceleration of heart beats in response to negative outcomes. However, it has often been used as a secondary measure to assess defensive responding to threat, along other more popular techniques. In this review, we aim at paving the road for its employment as an additional tool in fear conditioning experiments in humans. After an overview of the studies carried out throughout the last century, we describe more recent evidence up to the most contemporary research insights. Lastly, we provide some guidelines concerning the best practices to adopt in human fear conditioning studies which aim to investigate fear-induced bradycardia.

The effect of gradual extinction training on the renewal of electrodermal conditional responses

Extinction, the repeated presentation of a conditional stimulus (CS) without the unconditional stimulus (US), is the standard paradigm to reduce conditional responding acquired by the repeated pairing of CS and US in acquisition. However, this reduction of conditional responding is prone to relapse. In rodent fear-conditioning, gradual extinction, the fading out of CS-US pairings during extinction, has been shown to reduce the return of fear. The current study replicated the gradual extinction procedure in human fear conditioning and assessed whether it reduced the return of fear due to ABA renewal and reacquisition. During extinction, one group received standard extinction, a second received gradual extinction (increasing the spacing of USs presented after the 1st, 3rd, 6th, 10th, and 15th CS+ trials), and a third received reversed extinction training (decreasing the spacing of USs presented after the 1st, 6th, 10th, 13th, and 15th CS+ trials). Larger renewal and faster reacquisition of differential electrodermal responses to CS+ and CS- were expected after standard and reversed extinction than after gradual extinction training. The results were inconclusive due to the failure to find extinction of differential electrodermal responses and US expectancy ratings in both gradual and reversed extinction groups. Despite successful extinction in group standard, renewal was only observed in US expectancy. Visualization of US expectancy ratings during extinction suggested that potential identification of the US presentation patterns during extinction in the gradual and reversed groups delayed extinction learning.

Intermittent theta burst stimulation over the left prefrontal cortex: no additional effect for virtual reality exposure therapy in acrophobia-a randomized trial

Anxiety disorders are the most prevalent mental health conditions. Besides psycho-pharmacotherapy, cognitive behavioral therapy with an exposure-based approach is considered the gold standard. However, not all patients benefit from this approach. Here, we aimed to translate laboratory findings on enhanced fear extinction with repetitive transcranial magnetic stimulation (TMS) to the clinic. In this double-blind, randomized, placebo-controlled clinical trial, 76 participants with acrophobia received an activating intermittent theta burst stimulation (iTBS) targeting the left posterior prefrontal cortex immediately before two virtual reality exposure therapy sessions. Phobic symptoms were assessed at baseline, post-intervention, and a 6-month follow-up. Results revealed a significant reduction in phobic symptoms from baseline to post-assessment and follow-up and confirmed the efficacy of virtual reality exposure therapy as a treatment for specific phobias. Interestingly, no additional effect was observed for active iTBS compared to sham iTBS. Our post-hoc analyses argue for an individualized TMS application. Further research is needed to determine optimal TMS parameters and validate these results in clinical trials, accounting for methodological and inter- and intra-individual variability, as well as alternative therapeutic processes.

The Organization of Anxiety Symptoms Along the Threat Imminence Continuum

Pathological anxiety is highly prevalent, impairing, and often chronic. Yet, despite considerable research, mechanistic understanding of anxiety and its translation to clinical practice remain limited. Here, we first highlight two foundational complications that contribute to this gap: a reliance on a phenomenology-driven definition of pathological anxiety in neurobiological mechanistic research, and a limited understanding of the chronicity of anxiety symptom expression. We then posit that anxiety symptoms may reflect aberrant expression of otherwise normative defensive responses. Accordingly, we propose that threat imminence, an organizing dimension for normative defensive responses observed across species, may be applied to organize and understand anxiety symptoms along a temporal dimension of expression. Empirical evidence linking distinct anxiety symptoms and the aberrant expression of imminence-dependent defensive responses is reviewed, alongside the neural mechanisms which may underpin these cognitive, physiological, and behavioral responses. Drawing from extensive translational and clinical research, we suggest that understanding anxiety symptoms through this neurobiologically-informed framework may begin to overcome the conceptual complications hindering advancement in mechanistic research and clinical interventions for pathological anxiety.

A preliminary study of threat-anticipatory responding in Latina youth: associations with age, anxiety, and cortical thickness

Variation in prefrontal cortex neuroanatomy has been previously associated with elevated physiological responses to anticipated aversive events. The extent to which such associations extend beyond the specific ecology of treatment-seeking youth from upper-middle socioeconomic backgrounds is unknown. The current study tests the replicability of neuroanatomical correlates of anticipatory responding and the moderating roles of age and anxiety severity in a community sample of Latina girls, a historically underrepresented group exhibiting high levels of untreated anxiety. Forty pre-adolescent Latina girls (MAge = 10.01, s.d. = 1.25, range = 8-12 years) completed a structural magnetic resonance imaging scan. Participants also completed a differential threat and safety learning paradigm, during which skin conductance and subjective fear responding were assessed. Anxiety severity was assessed via the Screen for Child Anxiety Related Emotional Disorders. Ventromedial prefrontal cortex thickness was associated with reduced physiological responsivity to anticipated threat. Age- and anxiety-dependent associations emerged between dorsomedial prefrontal cortex thickness and individual differences in subjective fear responding to anticipated threat. This preliminary study extends work on neuroanatomical contributions to physiological threat responsivity to a community sample of Latina youth and highlights potential considerations for early identification efforts in this population when threat neurocircuitry is still developing.