Fear Renewal Research Articles

GluA1 phosphorylation at serine 831 in the lateral amygdala is required for fear renewal

Fear renewal, a widely pursued model of post-traumatic stress disorder and phobias, refers to the context-specific relapse of conditioned fear after extinction. However, its molecular mechanisms are largely unknown. We found that renewal-inducing stimuli, generally believed to be insufficient to induce synaptic plasticity, enhanced excitatory synaptic strength, activity of synaptic GluA2-lacking AMPA receptors and Ser831 phosphorylation of synaptic surface GluA1 in the lateral nucleus of the amygdala (LAn) of fear-extinguished rats. Consistently, the induction threshold for LAn synaptic potentiation was considerably lowered after extinction, and renewal occluded this low-threshold potentiation. The low-threshold potentiation (a potential cellular substrate for renewal), but not long-term potentiation, was attenuated by dialysis into LAn neurons of a GluA1-derived peptide that competes with Ser831-phosphorylated GluA1. Microinjections of the same peptide into the LAn attenuated fear renewal, but not fear learning. Our findings suggest that GluA1 phosphorylation constitutes a promising target for clinical treatment of aberrant fear-related disorders.

Fear of the unexpected: Hippocampus mediates novelty-induced return of extinguished fear in rats

Several lines of evidence indicate an important role for the hippocampus in the recovery of fear memory after extinction. For example, hippocampal inactivation prevents the renewal of fear to an extinguished conditioned stimulus (CS) when it is presented outside the extinction context. Renewal of extinguished responding is accompanied by associative novelty (an unexpected occurrence of a familiar CS in a familiar place), the detection of which may require the hippocampus. We therefore examined whether the hippocampus also mediates the recovery of extinguished fear caused by other unexpected events, including presenting a familiar CS in a novel context or presenting a novel cue with the CS in a familiar context (e.g., external disinhibition). Rats underwent Pavlovian fear conditioning and extinction using an auditory CS and freezing behavior served as the index of conditioned fear. In Experiment 1, conditioned freezing to the extinguished CS was renewed in a novel context and this was eliminated by intra-hippocampal infusions of the GABAA agonist, muscimol, prior to the test. In Experiment 2, muscimol inactivation of the hippocampus reduced the external disinhibition of conditioned freezing that occurred when a novel white noise accompanied the extinguished tone CS. Collectively, these results suggest that the hippocampus mediates the return of fear when extinguished CSs are unexpected, or when unexpected stimuli accompany CS presentation. Ultimately, a violation of expectations about when, where, and with what other stimuli an extinguished CS will occur may form the basis of spontaneous recovery, renewal, and external disinhibition.

Prefrontal microcircuit underlies contextual learning after hippocampal loss

Specific brain circuits have been classically linked to dedicated functions. However, compensation following brain damage suggests that these circuits are capable of dynamic adaptation. Such compensation is exemplified by Pavlovian fear conditioning following damage to the dorsal hippocampus (DH). Although the DH normally underlies contextual fear and fear renewal after extinction, both can be learned in the absence of the DH, although the mechanisms and nature of this compensation are currently unknown. Here, we report that recruitment of alternate structures, specifically the infralimbic and prelimbic prefrontal cortices, is required for compensation following damage to the hippocampus. Disconnection of these cortices in DH-compromised animals and immediate early gene induction profiles for amygdala-projecting prefrontal cells revealed that communication and dynamic rebalancing within this prefrontal microcircuit is critical. Additionally, the infralimbic cortex normally plays a role in limiting generalization of contextual fear. These discoveries reveal that plasticity through recruitment of alternate circuits allows the brain to compensate following damage, offering promise for targeted treatment of memory disorders.

Ventral Hippocampal Kappa Opioid Receptors Mediate the Renewal of Fear following Extinction in the Rat

The hippocampus is part of a neural network which regulates the renewal of fear following extinction. Both the ventral (VH) and dorsal (DH) hippocampus have been shown to be necessary for renewal, however the critical receptors and neurotransmitters mediating these contributions are poorly understood. One candidate mechanism is the kappa opioid receptor (KOR) system, which has been implicated in fear learning and anxiety. Here we examined the effect of the KOR antagonist norbinaltorphamine hydrochloride (norBNI), infused into either the VH or DH, on the renewal of extinguished fear. We found that an infusion of norBNI into the VH significantly reduced the relapse of fear on test compared to that seen in saline controls (Experiment 1), while similar infusions of norBNI into the DH had no effect on renewal (Experiment 2). These findings show that hippocampal KORs are involved in fear renewal and also identify a dissociation in the contribution of VH and DH KORs to the expression of renewed fear.

The effect of a retrieval cue on the return of spider fear

Background and objectivesExposure therapy is often used as treatment for anxiety disorders. However, a change in context after exposure can result in fear renewal. This renewal can be attenuated by using retrieval cues stemming from the exposure context. The present study investigated the effect of such a cue in spider-fearful persons. MethodsThirty-three participants underwent an in vivo exposure session while wearing a bracelet (retrieval cue). After exposure, half of the participants continued to wear the bracelet at home until follow-up (cue groups); the other half handed over the bracelet after exposure (no cue groups). Half of the participants in each group received the follow-up in the exposure context (AAcue and AAnocue); for the other half follow-up was conducted in a novel environment (ABcue and ABnocue). ResultsA switch in context at follow-up resulted in more self-reported anxiety and arousal compared to no switch. However, the retrieval cue did not attenuate this renewed responding. LimitationsThe number of participant per condition was limited, which might have obscured possible retrieval cue effects due to a lack of power. Additionally, information about the retrieval cue was provided after exposure, which might have weakened the association between the cue and exposure therapy. Furthermore, no autonomic measures were incorporated, restricting the effect to self-report measures. For future studies we would recommend to explicitly link the retrieval cue before onset of the exposure session and to incorporate autonomic measures. ConclusionsOur findings indicate that a switch in context resulted in more self-reported anxiety and arousal, but that a cue stemming from the exposure context did not attenuate this renewal.

Acute early-life stress results in premature emergence of adult-like fear retention and extinction relapse in infant rats.

Recent studies have shown that chronic early life stress results in precocious expression of the adult-like phenotype of fear retention and inhibition. However, it is unknown whether the experience of acute early trauma has the same effects as exposure to chronic early stress. In the present study, a 24-hr period of maternal deprivation on postnatal day (P) 9 was used as an acute early life stressor. In infancy (P16-17), maternally deprived and standard-reared rats were conditioned to fear a noise paired with shock. In Experiments 1 and 2, fear to the noise was then extinguished before rats were tested for context-mediated fear renewal or stress-induced fear reinstatement. In Experiments 3a and 3b, conditioned rats were tested for fear retention 1, 7, or 14 days after training. Whereas standard-reared infants exhibited relapse-resistant extinction and infantile amnesia (i.e., behaviors typical of their age), maternally deprived infants exhibited the renewal and reinstatement effects (i.e., relapse-prone extinction) and showed good retention of fear over the 7- and 14-day intervals (i.e., infantile amnesia was reduced). In other words, similar to rats exposed to chronic early life stress, rats exposed to acute early stress expressed an adult-like profile of fear retention and inhibition during infancy. These findings suggest that similar mechanisms might be involved in the effects of acute and chronic stress on emotional development, and may have implications for our understanding and treatment of emotional disorders associated with early adversity.

Extinction of reinstated or ABC renewed fear responses renders them resistant to subsequent ABA renewal.

Three experiments used an ABA renewal paradigm to study deepening of response loss produced by extinction of reinstated or ABC renewed fear responses. In Experiment 1, rats were trained with two stimuli, S1 and S2, in context A and extinguished to S1 in context B and S2 in context C, shocked in B but not in C, and subjected to additional extinction of S1 in B and S2 in C. Rats froze less to S1 than S2 when subsequently tested in A. In Experiments 2 and 3, following training of S1 and S2 in A, one group received extinction of S1 in B and S2 in C followed by extinction of S1 in C and S2 in B. This group froze less to S1 in A or to S2 in a novel context, D, than a group always extinguished to S1 in B and S2 in C or a group extinguished to both S1 and S2 in B and C. These results show that additional extinction of a conditioned stimulus (conditional stimulus [CS]) exhibiting either reinstatement or ABC renewal renders that CS resistant to ABA renewal. They are consistent with theories that allow a role for context in extinction learning and that use error-correction mechanisms to update this learning.

Effect of multiple context exposure on renewal in spider phobia

BackgroundRenewal of fear is one form of relapse that occurs after successful exposure therapy as a result of an encounter with a feared object in a context different from the exposure context. The current study is the first to examine whether virtual reality (VR) exposure conducted in multiple contexts reduces the likelihood of renewal. MethodThirty spider-phobic patients were randomly allocated to one of two groups that were exposed to a virtual spider four times either in a single context or in multiple contexts. All participants completed a renewal test in a novel virtual context, and an in-vivo behavior avoidance test with a real spider before and after exposure. ResultsAs reflected in the ratings, skin conductance level, and behavioral measures, the fear of spiders decreased significantly in both groups within and between the exposure trials and from pre to post exposure. Importantly, extinction in multiple contexts was able to significantly reduce renewal compared to extinction in a single context. ConclusionsBased on highly controlled context manipulations using VR, this study was able to successfully transfer animal work to phobic patients. These findings strongly suggest that exposure in multiple contexts improves the generalizability of exposure to a new context. Consequently, we recommend the application of multiple context exposures in a clinical setting to reduce the likelihood of renewal. In addition, virtual reality was demonstrated to be a helpful tool for inducing contextual shifts during the exposures.

Correlations between psychological tests and physiological responses during fear conditioning and renewal

BackgroundAnxiety disorders are characterized by specific emotions, thoughts and physiological responses. Little is known, however, about the relationship between psychological/personality indices of anxiety responses to fear stimuli.MethodsWe studied this relationship in healthy subjects by comparing scores on psychological and personality questionnaires with results of an experimental fear conditioning paradigm using a visual conditioned stimulus (CS). We measured skin conductance response (SCR) during habituation, conditioning, and extinction; subsequently testing for recall and renewal of fear 24 hours later.ResultsWe found that multiple regression models explained 45% of the variance during conditioning to the CS+, and 24% of the variance during renewal of fear to the CS+. Factors that explained conditioning included lower levels of conscientiousness, increased baseline reactivity (SCL), and response to the shock (UCR). Low levels of extraversion correlated with greater renewal. No model could be found to explain extinction learning or extinction recall to the CS+.ConclusionsThe lack of correlation of fear extinction with personality and neuropsychological indices suggests that extinction may be less determined by trait variables and cognitive state, and may depend more on the subject’s current emotional state. The negative correlation between fear renewal and extraversion suggests that this personality characteristic may protect against post-treatment relapse of symptoms of anxiety disorders.

Cholinergic Blockade Frees Fear Extinction from Its Contextual Dependency

Fears that are maladaptive or inappropriate can be reduced through extinction training. However, extinction is highly context-sensitive, resulting in the renewal of fear after shifts in context and limiting the clinical efficacy of extinction training. Lesion and inactivation studies have shown that the contextualization of extinction depends on the hippocampus. Parallel studies have found that intrahippocampal scopolamine (Scop) blocks contextual fear conditioning. Importantly, this effect was replicated with a noninvasive technique in which a low dose of Scop was administered systemically. We aimed to transfer the effects of this noninvasive approach to block the contextualization of fear extinction. Rats were tone fear conditioned and extinguished under various systemic doses of Scop or the saline vehicle. They were subsequently tested (off drug) for tone fear in a context that was the same (control subjects) or shifted (renewal group) with respect to the extinction context. The lowest dose of Scop produced a significant attenuation of fear renewal when renewal was tested either in the original training context or a novel context. The drug also slowed the rate of long-term extinction memory formation, which was readily overcome by extending extinction training. Scopolamine only gave this effect when it was administered during but not after extinction training. Higher doses of Scop severely disrupted extinction learning. We discovered that disrupting contextual processing during extinction with the cholinergic antagonist Scop blocked subsequent fear renewal. Low doses of Scop might be a clinically promising adjunct to exposure therapy by making extinction more relapse-resistant.

P300/CBP-Associated Factor Selectively Regulates the Extinction of Conditioned Fear

It is well established that the activity of chromatin-modifying enzymes is crucial for regulating gene expression associated with hippocampal-dependent memories. However, very little is known about how these epigenetic mechanisms influence the formation of cortically dependent memory, particularly when there is competition between opposing memory traces, such as that which occurs during the acquisition and extinction of conditioned fear. Here we demonstrate, in C57BL/6 mice, that the activity of p300/CBP-associated factor (PCAF) within the infralimbic prefrontal cortex is required for long-term potentiation and is necessary for the formation of memory associated with fear extinction, but not for fear acquisition. Further, systemic administration of the PCAF activator SPV106 enhances memory for fear extinction and prevents fear renewal. The selective influence of PCAF on fear extinction is mediated, in part, by a transient recruitment of the repressive transcription factor ATF4 to the promoter of the immediate early gene zif268, which competitively inhibits its expression. Thus, within the context of fear extinction, PCAF functions as a transcriptional coactivator, which may facilitate the formation of memory for fear extinction by interfering with reconsolidation of the original memory trace.

Extinction treatment in multiple contexts attenuates ABC renewal in humans

Renewal has been implicated as one of the underlying mechanisms in return of fear following exposure therapy. ABC renewal is clinically more relevant than ABA renewal and yet it is a weaker form of renewal, suggesting that conducting extinction treatment in multiple contexts may be sufficient to attenuate ABC renewal. Using self-reported expectancy of shock and startle blink responses the current study examined the effects of conducting extinction treatment in multiple contexts on ABC fear renewal. Participants (N = 68) received conditional stimulus (CS) and unconditional stimulus (US) pairings in one context (A) followed by extinction treatment (CS presentations alone) in either one other context (B) or three other contexts (BCD). Non-reinforced test trials in a novel context (E) resulted in renewal of extinguished conditioned behaviour for those who received extinction in only one context. However, renewal was attenuated for those who received extinction treatment in three contexts. No renewal was found for the control group that received the test trial in the same context as during extinction. Suggestions are provided for clinicians seeking to prevent or attenuate return of fear following exposure therapy.

No erasure effect of retrieval–extinction trial on fear memory in the hippocampus-independent and dependent paradigms

Recently, Monfils et al. [9] and Clem and Huganir [3] have shown that an isolated retrieval trial before the extinction sessions (retrieval–extinction) in mice and rats prevented the renewal and spontaneous recovery of the original fear memory by inhibiting reconsolidation in a hippocampus-independent manner. In contrast, Chan et al. [2], using the same paradigm, reported that retrieval extinction in rats augmented the renewal and reinstatement of extinguished fear. However, it remains unclear whether or not retrieval extinction in a hippocampus-independent paradigm erases the original fear memory by inhibiting reconsolidation. We therefore conducted three experiments to investigate whether or not retrieval extinction erases the original fear memory by inhibiting reconsolidation in mice. Our major findings were as follows. (1) Retrieval–extinction in mice did not suppress spontaneous recovery and fear renewal in a hippocampus-independent paradigm. (2) Fear renewal was observed when retrieval–strong extinction in a hippocampus-independent paradigm was performed. (3) Retrieval extinction in a hippocampus-dependent paradigm did not erase the original fear memory. These results suggested that fear extinction after retrieval in mice does not inhibit reconsolidation of previously consolidated fear memory in either a hippocampus-independent or -dependent paradigm.

Context Effects on Habituation to Disgust-Relevant Stimuli

Although exposure-based treatments appear to be efficacious for the treatment of anxiety-related disorders, many individuals experience a renewal of the original fear response at follow-up. In an effort to prevent fear renewal, researchers have begun to use exposure of the conditioned stimulus in different contexts during extinction. Although studies continue to accumulate, showing that conducting exposure in multiple contexts buffers against the renewal of distress responses to fear-relevant stimuli, it remains unclear how conducting exposure in multiple contexts affects the renewal of distress responses to disgust-relevant stimuli. In the present study, participants (N = 52) were randomized to repeated presentations of disgust stimuli (vomiting in a toilet) in a single context or multiple contexts. Results revealed that those in the single context condition reported less distress after the exposure manipulation compared with the multiple context condition. Although there were no significant group differences in distress toward a novel disgust stimulus, the single context condition reported greater distress renewal than the multiple context condition. Furthermore, individuals in the multiple context condition showed significant reductions in distress at 1-week follow-up whereas distress in the single context condition remained stable. Subsequent analyses also provided moderate evidence for an effect of the disgust context manipulation on physiological arousal and disgust propensity, but not disgust-related behavioral avoidance. These findings offer preliminary evidence that renewal of distress toward disgust cues can be attenuated by conducting extinction in multiple contexts.

Enhancement of Extinction Memory and Prefrontal Cortex Metabolic Capacity Via Low-Level Light Therapy (P07.176)

Objective: To determine the ability of low-level light therapy (LLLT) to modulate memory and brain energy metabolism in vivo. Background LLLT enhances the metabolic capacity of neurons in culture through stimulation of the mitochondrial enzyme cytochrome oxidase, but the in vivo effects of LLLT on brain and behavior are poorly characterized. Design/Methods: This study tested the hypothesis that transcranial LLLT facilitates fear extinction memory and prevents the reemergence of extinguished conditioned fear responses via enhancement of brain metabolic capacity in rats. Long-Evans rats were trained in a Pavlovian fear-conditioning paradigm consisting of two sessions of four tone-foot shock presentations. Subsequently, rats underwent extinction training and LLLT was delivered at λ= 660 nm, 5.4 J/cm2, 15 min after each extinction session. Freezing behavior scores were compared to those of control rats (undergoing fear-conditioning training but no LLLT). Effects of LLLT on brain metabolism were determined through measurement of prefrontal cortex oxygen concentration with fluorescent quenching oximetry and brain cytochrome oxidase histochemistry. Results: LLLT-treated rats showed an enhanced rate of extinction, with freezing levels 59 and 70% lower than control, after the 2nd and 3rd extinction sessions. After the 4th extinction session, LLLT-treated rats showed a paradoxical increase in freezing, compared to control. However, LLLT-treated rats showed decreased rates of fear renewal compared to controls. Also, LLLT increased the rate of in situ oxygen consumption in the prefrontal cortex, and induced a hormetic dose-response effect on the metabolic capacity of the prefrontal cortex, with a low dose showing the largest (12%) increase as compared to control. Conclusions: The data demonstrate that in vivo transcranial LLLT can be used to enhance the metabolic capacity of the brain and to facilitate retention of extinction memories, and implicate LLLT as a potential intervention to improve memory in humans. Supported by: NIH grants R01 NS37755 and T32 MH65728 directed by Prof. F. Gonzalez-Lima. Disclosure: Dr. Martinez has nothing to disclose. Dr. Bruchey has nothing to disclose. Dr. Gonzalez-Lima has nothing to disclose.

The European Culture Wars in Ireland: The Callan Schools Affair, 1868-81, by Colin Barr

Colin Barr’s question in this book is why there was no Prussian style Kulturkampf in Ireland. After the declaration of papal infallibility at the Vatican Council in 1870–71, and the renewed fear of Catholic aggression and the political struggles which that declaration precipitated in much of continental Europe—and also given the existence of anti-Catholicism among British political élites—why did a seemingly tailor-made opportunity not lead the government to curtail the power of the Catholic Church? The provocation was provided by the experiences and efforts of Fr Robert O’Keeffe, parish priest of Callan in Kilkenny county. In the late 1860s O’Keeffe ran into difficulties with his bishop and was suspended as a priest, whereupon his roles as manager in the local national schools and chaplain in the Workhouse were discontinued by different government agencies. These civic bodies could be seen as enforcing the discipline of the Roman church—anathema to many who saw Rome as riding roughshod over the rights of individual citizens. Challenging the whole canon law basis and process for his suspension, O’Keeffe sued for libel anyone who said he was suspended (not only his bishop but ultimately Cardinal Cullen, his own curates, and many others), repeatedly dragging canon law into the civil courts. He also rallied local support around Callan, wrote public letters, and published extensive pamphlets defending himself. Moreover, he assiduously sought help from politicians at the highest levels, meeting with the Prime Minister, Gladstone, and being helped by a former Prime Minister, Russell, as well as by many others from within and outside Parliament. In the first half of the 1870s the Callan Affair became a cause célèbre not just in Ireland but throughout the United Kingdom and even around the world.

A modified counterconditioning procedure prevents the renewal of conditioned fear in rats

Two studies using an ABA design examined the Extinction and renewal of conditioned barpress suppression. Following lights-off and foot shock pairings in Context A, rats were placed in Context B and were given either a standard counterconditioning procedure where the lights-off CS was paired with a novel food US delivered freely or a modified counterconditioning procedure where CS-US pairings only occurred if the rat earned the US by performing a required behavior during the CS. Results indicated that the modified counterconditioning procedure thwarted ABA renewal but the conventional counterconditioning procedure did not reduce ABA renewal any more than nonreinforced exposure to the CS alone. Furthermore, the response required during the modified counterconditioning procedure could be one used as a baseline response during Acquisition of fear or it could be a novel response. Implications of the results for theories of Extinction and renewal of fear are discussed.

Extinction, generalization, and return of fear: A critical review of renewal research in humans

The main behavioral signature of fear extinction is its fragility. This is exemplified by the renewal effect, where a change in the background context produces recovery of fear to a conditioned-and-extinguished stimulus. Renewal is the backbone of a widely accepted theory of extinction in animal research, as well as an important experimental model to screen novel treatment techniques. This has led to an explosion of fear renewal research in humans. However, the mere observation of return of fear in a renewal procedure is not sufficient to validate this particular theory of extinction in the tested sample/procedure. Here, we systematically outline a set of experimental tests that aid in evaluating alternative extinction/renewal mechanisms. We examine published renewal studies in human fear conditioning and conclude that the prevailing theory of extinction is often taken for granted, but critical tests are lacking. Including these tests in future research will not only reveal the fear extinction mechanism in humans, but also inspire further developments in extinction treatment research.

Single prolonged stress disrupts retention of extinguished fear in rats

Clinical research has linked post-traumatic stress disorder (PTSD) with deficits in fear extinction. However, it is not clear whether these deficits result from stress-related changes in the acquisition or retention of extinction or in the regulation of extinction memories by context, for example. In this study, we used the single prolonged stress (SPS) animal model of PTSD and fear conditioning procedures to examine the effects of prior traumatic stress on the acquisition, retention, and context-specificity of extinction. SPS administered one week prior to fear conditioning had no effect on the acquisition of fear conditioning or extinction but disrupted the retention of extinction memories for both contextual and cued fear. This SPS effect required a post-stress incubation period to manifest. The results demonstrate that SPS disrupts extinction retention, leading to enhanced fear renewal; further research is needed to identify the neurobiological processes through which SPS induces these effects.

Hippocampal and Prefrontal Projections to the Basal Amygdala Mediate Contextual Regulation of Fear after Extinction

Knowing when and where to express fear is essential to survival. Recent work in fear extinction paradigms reveals that the contextual regulation of fear involves a neural network involving the hippocampus, medial prefrontal cortex, and amygdala. The amygdaloid basal nuclei (BA) receive convergent input from the ventral hippocampus (VH) and prelimbic (PL) prefrontal cortex and may integrate VH and PL input to regulate fear expression. To examine the functional organization of this neural circuit, we used cellular imaging of c-fos expression in anatomically defined neuronal populations and circuit disconnections to identify the pathways involved in the contextual control of extinguished fear. Before behavioral testing, we infused a retrograde tracer into the amygdala to label BA-projecting neurons in VH and PL. Rats then underwent fear conditioning and extinction and were tested for their fear to the extinguished conditioned stimulus (CS) in either the extinction context or in another context; freezing behavior served as the index of conditional fear. CS presentation outside the extinction context renewed conditional freezing and was associated with significantly more c-fos expression in BA-projecting neurons in the VH and PL than that induced by CS presentation in the extinction context. We next examined whether direct or indirect projections of VH to BA mediate fear renewal. Interestingly, disconnections of the VH from either the BA or PL eliminated renewal. These findings suggest that convergent inputs from both the VH and PL in the BA mediate the contextual control of fear after extinction.