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"fear memory"
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A Systematic Review on the Effect of Transcranial Direct Current and Magnetic Stimulation on Fear Memory and Extinction
Anxiety disorders are among the most prevalent mental disorders. Present treatments such as cognitive behavior therapy and pharmacological treatments show only moderate success, which emphasizes the importance for the development of new treatment protocols. Non-invasive brain stimulation methods such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) have been probed as therapeutic option for anxiety disorders in recent years. Mechanistic information about their mode of action, and most efficient protocols is however limited. Here the fear extinction model can serve as a model of exposure therapies for studying therapeutic mechanisms, and development of appropriate intervention protocols. We systematically reviewed 30 research articles that investigated the impact of rTMS and tDCS on fear memory and extinction in animal models and humans, in clinical and healthy populations. The results of these studies suggest that tDCS and rTMS can be efficient methods to modulate fear memory and extinction. Furthermore, excitability-enhancing stimulation applied over the vmPFC showed the strongest potential to enhance fear extinction. We further discuss factors that determine the efficacy of rTMS and tDCS in the context of the fear extinction model and provide future directions to optimize parameters and protocols of stimulation for research and treatment.
Journal Article
Effects of the histone deacetylase inhibitor valproic acid in combination with fear-memory retrieval before exposure therapy for spider phobia: A randomized controlled trial
Return of fear after successful exposure therapy for a phobia is a common clinical challenge. A previous study on mice demonstrated that the persistent attenuation of remote fear memories can be achieved by combining histone deacetylase inhibitors (HDACis) with fear-memory retrieval prior to extinction training.
To evaluate the translational potential of this approach, we conducted a randomized, double-blind, placebo-controlled trial. Forty-eight individuals with DSM-IV spider phobia received either HDACi valproic acid (VPA, 500 mg) or a placebo prior to the retrieval of fear memory, followed by exposure therapy in virtual reality.
No significant group difference was found in terms of behavioral change on the behavioral approach test at 3 months follow-up and baseline (primary outcome). However, the VPA group displayed significantly reduced fear in two self-report questionnaires related to spider phobia (Fear of Spiders Questionnaire; Spider Phobia Beliefs Questionnaire) as compared to the placebo group. No group differences were observed for psychophysiological indicators of fear.
The favorable impact of a single administration of VPA in combination with fear-memory retrieval prior to exposure therapy suggests that it might be an effective way to enhance symptom improvement at the subjective level in the treatment of phobias. Further studies need to investigate the conditions under which an improvement on the psychophysiological and behavioral levels can be achieved as well.
Journal Article
Auditory stimuli suppress contextual fear responses in safety learning independent of a possible safety meaning
Safety learning allows the identification of non-threatening situations, a learning process instrumental for survival and psychic health. In contrast to fear learning, in which a sensory cue (conditioned stimulus, CS) is temporally linked to a mildly aversive stimulus (US), safety learning is studied by presenting the CS and US in an explicitly unpaired fashion. This leads to conditioned inhibition of fear responses, in which sensory cues can acquire a safety meaning (CS-). In one variant of safety learning, an auditory CS- was shown to reduce contextual fear responses during recall, as measured by freezing of mice. Here, we performed control experiments to test whether auditory stimuli might interfere with freezing by mechanisms other than safety learning, a phenomenon also called external inhibition. Surprisingly, when auditory stimulation was omitted during training (US-only controls), such stimuli still significantly suppressed contextual freezing during recall, indistinguishable from the reduction of freezing after regular safety training. The degree of this external inhibition was positively correlated with the levels of contextual freezing preceding the auditory stimulation. Correspondingly, in fear learning protocols which employ a new context during recall and therefore induce lower contextual freezing, auditory stimuli did not induce significant external inhibition. These experiments show that in safety learning protocols that employ contextual freezing, the freezing reduction caused by auditory stimuli during recall is dominated by external inhibition, rather than by learned safety. Thus, in safety learning experiments extensive controls should be performed to rule out possible intrinsic effects of sensory cues on freezing behavior.
Journal Article
Time-dependent Potentiation of False Context Fear Memory Through Glucocorticoid Receptor Activation and Mineralocorticoid Receptor Inactivation
Background: Hypothalamic corticotropin-releasing factor (CRF) has been implicated in the formation of false contextual fear memory. Here, we examined the involvement of glucocorticoid (GR) and mineralocorticoid receptors (MR) in this process. Methods: Adult male C57BL/6J mice were exposed to Context B, similar but distinct from Context A, 3 h (B-3 h) after electric foot shock (FS) in Context A, and re-exposed to Context B either 24 h (B-24 h) or 9 days (B-9 d) after FS in Context A. To assess the effect of B-3 h exposure on the specificity of original memory, freezing levels were also measured in Context A (A-24 h or A-9 d) in a separate group, following the B-3 h exposure after FS. GR and MR protein levels in the hippocampal nuclear fractions were analyzed by western blotting. In pharmacological studies, dexamethasone (a GR agonist), fludrocortisone (an MR agonist), and mifepristone (a GR antagonist) were subcutaneously administered to hypothalamic CRF knockdown mice. Results: When mice were exposed to B-3 h after FS, they exhibited increased freezing at B-24 h compared with B-3 h and showed further increases at B-9 d compared with B-24 h, indicating a time-dependent intensification of false contextual fear memory. In contrast, freezing behavior in Context A was reduced at A-24 h and A-9 d after B-3 h exposure compared with mice that were not exposed to B-3 h, suggesting diminished precision of the original memory. Immunoblotting revealed increased nuclear GR levels at B-3 h and decreased MR levels at B-24 h and B-9 d. In CRF knockdown mice, dexamethasone enhanced freezing at B-3 h, whereas fludrocortisone reduced freezing at B-24 h and B-9 d. Co-administration of mifepristone and fludrocortisone suppressed both the formation of false memory at B-3 h and its subsequent enhancement. However, this treatment increased freezing in Context A at A-24 h and A-9 d following B-3 h exposure. Conclusion: Exposure to a similar but distinct context shortly after FS induces false contextual fear memory via GR activation and promotes its time-dependent potentiation through MR inactivation. Such early exposure may also impair the specificity of the original fear memory.
Journal Article
Formation of False Context Fear Memory Is Regulated by Hypothalamic Corticotropin-Releasing Factor in Mice
Traumatic events frequently produce false fear memories. We investigated the effect of hypothalamic corticotropin-releasing factor (CRF) knockdown (Hy-Crf-KD) or overexpression (Hy-CRF-OE) on contextual fear memory, as fear stress-released CRF and hypothalamic–pituitary–adrenal axis activation affects the memory system. Mice were placed in a chamber with an electric footshock as a conditioning stimulus (CS) in Context A, then exposed to a novel chamber without CS, as Context B, at 3 h (B-3h) or 24 h (B-24h). The freezing response in B-3h was intensified in the experimental mice, compared to control mice not exposed to CS, indicating that a false fear memory was formed at 3 h. The within-group freezing level at B-24h was higher than that at B-3h, indicating that false context fear memory was enhanced at B-24h. The difference in freezing levels between B-3h and B-24h in Hy-Crf-KD mice was larger than that of controls. In Hy-CRF-OE mice, the freezing level at B-3h was higher than that of control and Hy-Crf-KD mice, while the freezing level in B-24h was similar to that in B-3h. Locomotor activity before CS and freezing level during CS were similar among the groups. Therefore, we hypothesized that Hy-Crf-KD potentiates the induction of false context fear memory, while Hy-CRF-OE enhances the onset of false fear memory formation.
Journal Article
Behavioral Phenotypes of Foxg1 Heterozygous Mice
FOXG1 syndrome (FS, aka a congenital variant of Rett syndrome) is a recently defined rare and devastating neurodevelopmental disorder characterized by various symptoms, including severe intellectual disability, autistic features, involuntary, and continuous jerky movements, feeding problems, sleep disturbances, seizures, irritability, and excessive crying. FS results from mutations in a single allele of the FOXG1 gene, leading to impaired FOXG1 function. Therefore, in establishing mouse models for FS, it is important to test if heterozygous (HET) mutation in the Foxg1 gene, mimicking genotypes of the human FS individuals, also manifests phenotypes similar to their symptoms. We analyzed HET mice with a null mutation allele in a single copy of Foxg1, and found that they show various phenotypes resembling the symptoms of the human FS individuals. These include increased anxiety in the open field as well as impairment in object recognition, motor coordination, and fear learning and contextual and cued fear memory. Our results suggest that Foxg1 HET mice recapitulate at least some symptoms of the human FS individuals.
Journal Article
Selective enhancement of fear extinction by inhibiting neuronal adenylyl cyclase 1 (AC1) in aged mice
Adenylyl cyclase 1 (AC1) is a selective subtype of ACs, which is selectively expressed in neurons. The activation of AC1 is activity-dependent, and AC1 plays an important role in cortical excitation that contributes to chronic pain and related emotional disorders. Previous studies have reported that human-used NB001 (hNB001, a selective AC1 inhibitor) produced analgesic effects in different animal models of chronic pain. However, the potential effects of hNB001 on learning and memory have been less investigated. In the present study, we found that hNB001 affected neither the induction nor the expression of trace fear, but selectively enhanced the relearning ability during the extinction in aged mice. By contrast, the same application of hNB001 did not affect recent, remote auditory fear memory, or remote fear extinction in either adult or aged mice. Furthermore, a single or consecutive 30-day oral administration of hNB001 did not affect acute nociceptive response, motor function, or anxiety-like behavior in either adult or aged mice. Our results are consistent with previous findings that inhibition of AC1 did not affect general sensory, emotional, and motor functions in adult mice, and provide strong evidence that inhibiting the activity of AC1 may be beneficial for certain forms of learning and memory in aged mice.
Journal Article
Memory consolidation during sleep and adult hippocampal neurogenesis
In anticipation of the massive burden of neurodegenerative disease within super-aged societies, great efforts have been made to utilize neural stem and progenitor cells for regenerative medicine. The capacity of intrinsic neural stem and progenitor cells to regenerate damaged brain tissue remains unclear, due in part to the lack of knowledge about how these newly born neurons integrate into functional circuitry. As sizable integration of adult-born neurons naturally occurs in the dentate gyrus region of the hippocampus, clarifying the mechanisms of this process could provide insights for applying neural stem and progenitor cells in clinical settings. There is convincing evidence of functional correlations between adult-born neurons and memory consolidation and sleep; therefore, we describe some new advances that were left untouched in our recent review.
Journal Article
Differential role of Rac in the basolateral amygdala and cornu ammonis 1 in the reconsolidation of auditory and contextual Pavlovian fear memory in rats
Rationale and objectives
A conditioned stimulus (CS) is associated with a fearful unconditioned stimulus (US) in the traditional fear conditioning model. After fear conditioning, the CS–US association memory undergoes the consolidation process to become stable. Consolidated memory enters an unstable state after retrieval and requires the reconsolidation process to stabilize again. Evidence indicates the important role of Rac (Ras-related C3 botulinum toxin substrate) in the acquisition and extinction of fear memory. In the present study, we hypothesized that Rac in the amygdala is crucial for the reconsolidation of auditory and contextual Pavlovian fear memory.
Methods
Auditory and contextual fear conditioning and microinjections of the Rac inhibitor NSC23766 were used to explore the role of Rac in the reconsolidation of auditory and contextual Pavlovian fear memory in rats.
Results
A microinjection of NSC23766 into the basolateral amygdala (BLA) but not central amygdala (CeA) or cornu ammonis 1 (CA1) immediately after memory retrieval disrupted the reconsolidation of auditory Pavlovian fear memory. A microinjection of NSC23766 into the CA1 but not BLA or CeA after memory retrieval disrupted the reconsolidation of contextual Pavlovian fear memory.
Conclusions
Our experiments demonstrate that Rac in the BLA is crucial for the reconsolidation of auditory Pavlovian fear memory, whereas Rac in the CA1 is critical for the reconsolidation of contextual Pavlovian fear memory.
Journal Article