Animals must respond to various threats to survive. Neurons that express calcitonin gene-related peptide in the parabrachial nucleus (CGRP
neurons) relay sensory signals that contribute to satiation ...and pain-induced fear behaviour, but it is unclear how they encode these distinct processes. Here, by recording calcium transients in vivo from individual neurons in mice, we show that most CGRP
neurons are activated by noxious cutaneous (shock, heat, itch) and visceral stimuli (lipopolysaccharide). The same neurons are inhibited during feeding, but become activated during satiation, consistent with evidence that CGRP
neurons prevent overeating. CGRP
neurons are also activated during consumption of novel foods or by an auditory cue that has previously been paired with electrical footshocks. Correspondingly, silencing of CGRP
neurons attenuates the expression of food neophobia and conditioned fear responses. Therefore, in addition to transducing primary sensory danger signals, CGRP
neurons promote affective-behavioural states that limit harm in response to potential threats.
Generalization of conditioned-fear, a core feature of post-traumatic stress disorder (PTSD), has been the focus of several recent neuroimaging studies. A striking outcome of these studies is the ...frequency with which neural correlates of generalization fall within hubs of well-established functional networks including salience (SN), central executive (CEN), and default networks (DN). Neural substrates of generalization found to date may thus reflect traces of large-scale brain networks that form more expansive neural representations of generalization. The present study includes the first network-based analysis of generalization and PTSD-related abnormalities therein.
fMRI responses in established intrinsic connectivity networks (ICNs) representing SN, CEN, and DN were assessed during a generalized conditioned-fear task in male combat veterans (N = 58) with wide-ranging PTSD symptom severity. The task included five rings of graded size. Extreme sizes served as conditioned danger-cues (CS+: paired with shock) and safety-cues (CS-), and the three intermediate sizes served as generalization stimuli (GSs) forming a continuum-of-size between CS+ and CS-. Generalization-gradients were assessed as behavioral and ICN response slopes from CS+, through GSs, to CS-. Increasing PTSD symptomatology was predicted to relate to less-steep slopes indicative of stronger generalization.
SN, CEN, and DN responses fell along generalization-gradients with levels of generalization within and between SN and CEN scaling with PTSD symptom severity.
Neural substrates of generalized conditioned-fear include large-scale networks that adhere to the functional organization of the brain. Current findings implicate levels of generalization in SN and CEN as promising neural markers of PTSD.
The amygdala plays key roles in fear and anxiety. Studies of the amygdala have largely focused on neuronal function and connectivity. Astrocytes functionally interact with neurons, but their role in ...the amygdala remains largely unknown. We show that astrocytes in the medial subdivision of the central amygdala (CeM) determine the synaptic and behavioral outputs of amygdala circuits. To investigate the role of astrocytes in amygdala-related behavior and identify the underlying synaptic mechanisms, we used exogenous or endogenous signaling to selectively activate CeM astrocytes. Astrocytes depressed excitatory synapses from basolateral amygdala via A
adenosine receptor activation and enhanced inhibitory synapses from the lateral subdivision of the central amygdala via A
receptor activation. Furthermore, astrocytic activation decreased the firing rate of CeM neurons and reduced fear expression in a fear-conditioning paradigm. Therefore, we conclude that astrocyte activity determines fear responses by selectively regulating specific synapses, which indicates that animal behavior results from the coordinated activity of neurons and astrocytes.
Acid sphingomyelinase (ASM) regulates a variety of physiological processes and plays an important role in emotional behavior. The role of ASM in fear-related behavior has not been investigated so ...far. Using transgenic mice overexpressing ASM (ASMtg) and ASM deficient mice, we studied whether ASM regulates fear learning and expression of cued and contextual fear in a classical fear conditioning paradigm, a model used to investigate specific attributes of post-traumatic stress disorder (PTSD). We show that ASM does not affect fear learning as both ASMtg and ASM deficient mice display unaltered fear conditioning when compared to wild-type littermates. However, ASM regulates the expression of contextual fear in a sex-specific manner. While ASM overexpression enhances the expression of contextual fear in both male and female mice, ASM deficiency reduces the expression of contextual fear specifically in male mice. The expression of cued fear, however, is not regulated by ASM as ASMtg and ASM deficient mice display similar tone-elicited freezing levels. This study shows that ASM modulates the expression of contextual fear but not of cued fear in a sex-specific manner and adds a novel piece of information regarding the involvement of ASM in hippocampal-dependent aversive memory.
Mental imagery may represent a weaker form of perception and, thus, mental images may be more ambiguous than visual percepts. If correct, the acquisition of fear would be less specific for imagined ...fears in comparison to perceptual fears, perhaps facilitating broader fear generalization. To test this idea, a two-day differential fear conditioning experiment (N = 98) was conducted. On day one, two groups of participants underwent differential fear conditioning such that a specific Gabor patch orientation (CS+) was paired with mild shocks (US) while a second Gabor patch of orthogonal orientation (CS-) was never paired with shock. Critically, one group imagined the Gabor patches and the other group was visually presented the Gabor patches. Next, both groups were presented visual Gabor patches of similar orientations (GCS) to the CS+. On day two, to assess the persistence of imagined fear, participants returned to the lab and were tested on the GCS devoid of shock. For day one, in contrast to our primary hypothesis, both self-report and skin conductance response measures did not show a significant interaction between the GCS and groups. On day two, both measures demonstrated a persistence of imagined fear, without US delivery. Taken together, rather than demonstrating an overgeneralization effect, the results from this study suggest that imagery-based fear conditioning generalizes to a similar extent as perceptually acquired fear conditioning. Further, the persistence of imagery-based fear may have unique extinction qualities in comparison to perceptual-based fear.
•On day one, the generalization of a fear created in one’s imagination was tested.•On day two, after a night of sleep, the persistence of a fear created in one’s imagination was tested.•An imagery-based fear appears to spread to perceptually similar stimuli, consistent with visual-based fear generalization.•After a night of sleep, an imagery-based fear persists, even without continued aversive reinforcement.
Rationale
To improve outcomes for patients undergoing extinction-based therapies (e.g., exposure therapy) for anxiety disorders such as post-traumatic stress disorder (PTSD), there has been interest ...in identifying pharmaceutical compounds that might facilitate fear extinction learning and recall. Oxytocin (OT) is a mammalian neuropeptide that modulates activation of fear extinction-based neural circuits and fear responses. Little is known, however, about the effects of OT treatment on conditioned fear responding and extinction in humans.
Objectives
The purpose of the present study was to assess the effects of OT in a fear-potentiated startle task of fear conditioning and extinction.
Methods
A double-blind, placebo-controlled study of 44 healthy human participants was conducted. Participants underwent a conditioned fear acquisition procedure, after which they were randomized to treatment group and delivered OT (24 IU) or placebo via intranasal (IN) spray. Forty-five minutes after treatment, participants underwent extinction training. Twenty-four hours later, subjects were tested for extinction recall.
Results
Relative to placebo, the OT group showed increased fear-potentiated startle responding during the earliest stage of extinction training relative to placebo; however, all treatment groups showed the same level of reduced responding by the end of extinction training. Twenty-four hours later, the OT group showed significantly higher recall of extinction relative to placebo.
Conclusions
The current study provides preliminary evidence that OT may facilitate fear extinction recall in humans. These results support further study of OT as a potential adjunctive treatment for extinction-based therapies in fear-related disorders.
Historicizing Fear is a historical interrogation of the use of fear as a tool to vilify and persecute groups and individuals from a global perspective, offering an unflinching look at racism, fearful ...framing, oppression, and marginalization across human history. The book examines fear and Othering from a historical context, providing a better understanding of how power and oppression are used in the present day. Contributors ground their work in the theory of Othering—the reductive action of labeling a person as someone who belongs to a subordinate social category defined as the Other—in relation to historical events, demonstrating that fear of the Other is universal, timeless, and interconnected. Chapters address the music of neo-Nazi white power groups, fear perpetuated through the social construct of black masculinity in a racially hegemonic society, the terror and racial cleansing in early twentieth-century Arkansas, the fear of drug-addicted Vietnam War veterans, the creation of fear by the Tang Dynasty, and more. Timely, provocative, and rigorously researched, Historicizing Fear shows how the Othering of members of different ethnic groups has been used to propagate fear and social tension, justify state violence, and prevent groups or individuals from gaining equality. Broadening the context of how fear of the Other can be used as a propaganda tool, this book will be of interest to scholars and students of history, anthropology, political science, popular culture, critical race issues, social justice, and ethnic studies, as well as the general reader concerned with the fearful framing prevalent in politics. Contributors: Quaylan Allen, Melanie Armstrong, Brecht De Smet, Kirsten Dyck, Adam C. Fong, Jeff Johnson, Łukasz Kamieński, Guy Lancaster, Henry Santos Metcalf, Julie M. Powell, Jelle Versieren
The past two decades have brought dramatic progress in the neuroscience of anxiety due, in no small part, to animal findings specifying the neurobiology of Pavlovian fear‐conditioning. Fortuitously, ...this neurally mapped process of fear learning is widely expressed in humans, and has been centrally implicated in the etiology of clinical anxiety. Fear‐conditioning experiments in anxiety patients thus represent a unique opportunity to bring recent advances in animal neuroscience to bear on working, brain‐based models of clinical anxiety. The current presentation details the neural basis and clinical relevance of fear conditioning, and highlights generalization of conditioned fear to stimuli resembling the conditioned danger cue as one of the more robust conditioning markers of clinical anxiety. Studies testing such generalization across a variety of anxiety disorders (panic, generalized anxiety disorder, and social anxiety disorder) with systematic methods developed in animals will next be presented. Finally, neural accounts of overgeneralization deriving from animal and human data will be described with emphasis given to implications for the neurobiology and treatment of clinical anxiety.
The ability to extinguish conditioned fear memory is critical for adaptive control of fear response, and its impairment is a hallmark of emotional disorders like post-traumatic stress disorder ...(PTSD). Fear extinction is thought to take place when animals form a new memory that suppresses the original fear memory. However, little is known about the nature and the site of formation and storage of this new extinction memory. Here we demonstrate that a fear extinction memory engram is formed and stored in a genetically distinct basolateral amygdala (BLA) neuronal population that drives reward behaviors and antagonizes the BLA’s original fear neurons. Activation of fear extinction engram neurons and natural reward-responsive neurons overlap significantly in the BLA. Furthermore, these two neuronal subsets are mutually interchangeable in driving reward behaviors and fear extinction behaviors. Thus, fear extinction memory is a newly formed reward memory.
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•Fear extinction memory requires formation of new engram cells•Fear extinction engram cells are formed and stored in BLA Ppp1r1b+ neurons•Fear extinction engram cells and reward cells are functionally interchangeable•Omission of expected aversive stimuli is rewarding
Zhang et al. demonstrate that fear extinction memory requires new engram cells to be formed and stored in BLA neurons that drive reward behaviors. Fear extinction engram cells and reward-responsive cells are functionally equivalent in driving reward behaviors and fear extinction. Fear extinction memory is a newly formed reward memory.
Abstract Background context Psychological factors including fear avoidance beliefs are believed to influence the development of chronic low back pain (LBP). Purpose The purpose of this study was to ...determine the prognostic importance of fear avoidance beliefs as assessed by the Fear Avoidance Beliefs Questionnaire (FABQ) and the Tampa Scale of Kinesiophobia for clinically relevant outcomes in patients with nonspecific LBP. Design/setting The design of this study was a systematic review. Methods In October 2011, the following databases were searched: BIOSIS, CINAHL, Cochrane Library, Embase, OTSeeker, PeDRO, PsycInfo, PubMed/Medline, Scopus, and Web of Science. To ensure the completeness of the search, a hand search and a search of bibliographies was conducted and all relevant references included. A total of 2,031 references were retrieved, leaving 566 references after the removal of duplicates. For 53 references, the full-text was assessed and, finally, 21 studies were included in the analysis. Results The most convincing evidence was found supporting fear avoidance beliefs to be a prognostic factor for work-related outcomes in patients with subacute LBP (ie, 4 weeks–3 months of LBP). Four cohort studies, conducted by disability insurance companies in the United States, Canada, and Belgium, included 258 to 1,068 patients mostly with nonspecific LBP. These researchers found an increased risk for work-related outcomes (not returning to work, sick days) with elevated FABQ scores. The odds ratio (OR) ranged from 1.05 (95% confidence interval CI 1.02–1.09) to 4.64 (95% CI, 1.57–13.71). The highest OR was found when applying a high cutoff for FABQ Work subscale scores. This may indicate that the use of cutoff values increases the likelihood of positive findings. This issue requires further study. Fear avoidance beliefs in very acute LBP (<2 weeks) and chronic LBP (>3 months) was mostly not predictive. Conclusions Evidence suggests that fear avoidance beliefs are prognostic for poor outcome in subacute LBP, and thus early treatment, including interventions to reduce fear avoidance beliefs, may avoid delayed recovery and chronicity.
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