Estradiol shifts interactions between the infralimbic cortex and central amygdala to enhance fear extinction memory in female rats.

There is growing evidence that estradiol (E2) enhances fear extinction memory consolidation. However, it is unclear how E2 influences the nodes of the fear extinction network to enhance extinction memory. This study begins to delineate the neural circuits underlying the influence of E2 on fear extinction acquisition and consolidation in female rats. After fear conditioning (day 1), naturally cycling female rats underwent extinction learning (day 2) in a low-E2 state, receiving a systemic administration of either E2 or vehicle prior to extinction training. Extinction memory recall was then tested 24 hr later (day 3). We measured immediate early gene c-fos expression within the extinction network during fear extinction learning and extinction recall. During extinction learning, E2 treatment increased centrolateral amygdala c-fos activity and reduced lateral amygdala activity relative to vehicle. During extinction recall, E2-treated rats exhibited reduced c-fos expression in the centromedial amygdala. There were no group differences in c-fos expression within the medial prefrontal cortex or dorsal hippocampus. Examining c-fos ratios with the infralimbic cortex (IL) revealed that, despite the lack of group differences within the IL, E2 treatment induced greater IL activity relative to both prelimbic cortex and central amygdala (CeA) activity during extinction memory recall. Only the relationship between IL and CeA activity positively correlated with extinction retention. In conclusion, E2 appears to modify interactions between the IL and the CeA in females, shifting from stronger amygdalar modulation of fear during extinction learning to stronger IL control during extinction recall. © 2016 Wiley Periodicals, Inc.

Contribution of estradiol levels and hormonal contraceptives to sex differences within the fear network during fear conditioning and extinction.

BACKGROUND: Findings about sex differences in the field of fear conditioning and fear extinction have been mixed. At the psychophysiological level, sex differences emerge only when taking estradiol levels of women into consideration. This suggests that this hormone may also influence sex differences with regards to activations of brain regions involved in fear conditioning and its extinction. Importantly, the neurobiological correlates associated with the use of hormonal oral contraceptives in women have not been fully contrasted against men and against naturally cycling women with different levels of estradiol. In this study, we begin to fill these scientific gaps. METHODS: We recruited 37 healthy men and 48 healthy women. Of these women, 16 were using oral contraceptives (OC) and 32 were naturally cycling. For these naturally cycling women, a median split was performed on their serum estradiol levels to create a high estradiol (HE) group (n = 16) and a low estradiol (LE) group (n = 16). All participants underwent a 2-day fear conditioning and extinction paradigm in a 3 T MR scanner. Using the 4 groups (men, HE women, LE women, and OC users) and controlling for age and coil type, one-way ANCOVAs were performed to look at significant activations within the nodes of the fear circuit. Using post-hoc analyses, beta-weights were extracted in brain regions showing significant effects in order to unveil the differences based on hormonal status (men, HE, LE, OC). RESULTS: Significant main effect of hormonal status group was found across the different phases of the experiment and in different sub-regions of the insular and cingulate cortices, amygdala, hippocampus, and hypothalamus. During conditioning, extinction and recall, most of the observed differences suggested higher activations among HE women relative to men. During the unconditioned response, however, a different pattern was observed with men showing significantly higher brain activations. CONCLUSIONS: Our data further support the important contribution of estradiol levels in the activation of brain regions underlying fear learning and extinction. The results highlight the need to document gonadal hormonal levels, menstrual cycle phase as well as oral contraceptive use in women in order to avoid overlooking sex differences when investigating the neurobiology of emotional regulation.

Protocol for studying extinction of conditioned fear in naturally cycling female rats.

Extinction of conditioned fear has been extensively studied in male rodents. Recently, there have been an increasing number of studies indicating that neural mechanisms for certain behavioral tasks and response behaviors are different in females and males. Using females in research studies can represent a challenge because of the variation of gonadal hormones during their estrous cycle. This protocol describes well-established procedures that are useful in investigating the role of estrogen in fear extinction memory consolidation in female rats. Phase of the estrous cycle and exogenous estrogen administration prior to extinction training can influence extinction recall 24 hr later. The vaginal swabbing technique for estrous phase identification described here aids the examination and manipulation of naturally cycling gonadal hormones. The use of this basic rodent model may further delineate the mechanisms by which estrogen can modulate fear extinction memory in females.

Sex differences in the neurobiology of fear conditioning and extinction: a preliminary fMRI study of shared sex differences with stress-arousal circuitry.

BACKGROUND: The amygdala, hippocampus, medial prefrontal cortex (mPFC) and brain-stem subregions are implicated in fear conditioning and extinction, and are brain regions known to be sexually dimorphic. We used functional magnetic resonance imaging (fMRI) to investigate sex differences in brain activity in these regions during fear conditioning and extinction. METHODS: Subjects were 12 healthy men comparable to 12 healthy women who underwent a 2-day experiment in a 3 T MR scanner. Fear conditioning and extinction learning occurred on day 1 and extinction recall occurred on day 2. The conditioned stimuli were visual cues and the unconditioned stimulus was a mild electric shock. Skin conductance responses (SCR) were recorded throughout the experiment as an index of the conditioned response. fMRI data (blood-oxygen-level-dependent [BOLD] signal changes) were analyzed using SPM8. RESULTS: Findings showed no significant sex differences in SCR during any experimental phases. However, during fear conditioning, there were significantly greater BOLD-signal changes in the right amygdala, right rostral anterior cingulate (rACC) and dorsal anterior cingulate cortex (dACC) in women compared with men. In contrast, men showed significantly greater signal changes in bilateral rACC during extinction recall. CONCLUSIONS: These results indicate sex differences in brain activation within the fear circuitry of healthy subjects despite similar peripheral autonomic responses. Furthermore, we found that regions where sex differences were previously reported in response to stress, also exhibited sex differences during fear conditioning and extinction.

Sex differences, gonadal hormones and the fear extinction network: implications for anxiety disorders.

Convergent data from rodents and human studies have led to the development of models describing the neural mechanisms of fear extinction. Key components of the now well-characterized fear extinction network include the amygdala, hippocampus, and medial prefrontal cortical regions. These models are fueling novel hypotheses that are currently being tested with much refined experimental tools to examine the interactions within this network. Lagging far behind, however, is the examination of sex differences in this network and how sex hormones influence the functional activity and reactivity of these brain regions in the context of fear inhibition. Indeed, there is a large body of literature suggesting that sex hormones, such as estrogen, do modulate neural plasticity within the fear extinction network, especially in the hippocampus.After a brief overview of the fear extinction network, we summarize what is currently known about sex differences in fear extinction and the influence of gonadal hormones on the fear extinction network. We then go on to propose possible mechanisms by which sex hormones, such as estrogen, may influence neural plasticity within the fear extinction network. We end with a discussion of how knowledge to be gained from developing this line of research may have significant ramifications towards the etiology, epidemiology and treatment of anxiety disorders.

Test-retest reliability during fear acquisition and fear extinction in humans.

AIMS: Classical fear conditioning and extinction has been used to understand the neurobiology of fear learning and its inhibition. The recall of an extinction memory involves the ventromedial prefrontal cortex and the amygdala, and patients with posttraumatic stress disorder (PTSD) have been shown to exhibit deficits in this process. Furthermore, extinction forms the basis of exposure therapies commonly used to treat PTSD patients. It is possible that effective pharmacological and/or psychological treatment regimens could influence the activity of these regions, and thereby increase the ability to retain an extinction memory. However, to test this, a fear conditioning and extinction paradigm must demonstrate within-subject reproducibility over time. We, therefore, sought to test the within-subject reliability of a previously used 2-day, classical fear conditioning and extinction paradigm. METHODS: Eighteen healthy participants participated in a 2-day paradigm on three occasions, each separated by at least 12 weeks. Conditioning and extinction took place on Day 1, and extinction recall and fear renewal were evaluated on Day 2 on each of the three occasions. The conditioned stimulus was a visual cue and the unconditioned stimulus was a mild electric shock to the fingers. Skin conductance was recorded throughout the experiment to measure conditioned responses. RESULTS: We found that conditioning and extinction recall were not significantly different across time and were correlated within subjects. CONCLUSION: These data illustrate the reliability of this paradigm and its potential usefulness in evaluating the influence of a given treatment on the fear extinction network in longitudinal within-subject designs.

Altered processing of contextual information during fear extinction in PTSD: an fMRI study.

Medial prefrontal cortical areas have been hypothesized to underlie altered contextual processing in posttraumatic stress disorder (PTSD). We investigated brain signaling of contextual information in this disorder. Eighteen PTSD subjects and 16 healthy trauma-exposed subjects underwent a two-day fear conditioning and extinction paradigm. On day 1, within visual context A, a conditioned stimulus (CS) was followed 60% of the time by an electric shock (conditioning). The conditioned response was then extinguished (extinction learning) in context B. On day 2, recall of the extinction memory was tested in context B. Skin conductance response (SCR) and functional magnetic resonance imaging (fMRI) data were collected during context presentations. There were no SCR group differences in any context presentation. Concerning fMRI data, during late conditioning, when context A signaled danger, PTSD subjects showed dorsal anterior cingulate cortical (dACC) hyperactivation. During early extinction, when context B had not yet fully acquired signal value for safety, PTSD subjects still showed dACC hyperactivation. During late extinction, when context B had come to signal safety, they showed ventromedial prefrontal cortex (vmPFC) hypoactivation. During early extinction recall, when context B signaled safety, they showed both vmPFC hypoactivation and dACC hyperactivation. These findings suggest that PTSD subjects show alterations in the processing of contextual information related to danger and safety. This impairment is manifest even prior to a physiologically-measured, cue-elicited fear response, and characterized by hypoactivation in vmPFC and hyperactivation in dACC.

La memoria de extinción está deteriorada en la esquizofrenia / Extinction memory is impaired in schizophrenia

Fundamento: La esquizofrenia se asocia con anomalías del procesamiento emocional y de la cognición social, que pueden ser consecuencia de la desorganización de los mecanismos neurales subyacentes, que determinan el aprendizaje emocionals y la memoria. Para investigar esta posibilidad, evaluamos la adquisición y la extinción de las respuestas condicionadas de miedo y el recuerdo tardío de la extinción en pacientes con esquizofrenia e individuos de control. Métodos: Durante 2 días, se sometió a 28 pacientes con esquizofrenia y a 18 individuos de control emparejados demográficamente con un procedimiento de condicionamiento del miedo, aprendizaje de la extinción y recuerdo de la extinción, en el cual, como índice de las respuestas condicionadas, se usó la magnitud de la respuesta de conductancia cutánea (RCC). Resultados: Durante la tarea de adquisición del miedo, el 83% de los individuos de control y el 57% de los pacientes mostraron sensibilidad neurovegetativa («respondedores») y los pacientes mostraron mayor RCC al estímulo no emparejado con el estímulo incondicionado (EI) que los individuos de control. Dentro del grupo de respondedores, no hubo diferencias entre pacientes e individuos de control en los niveles de aprendizaje de la extinción; sin embargo, en comparación con los individuos de control, los pacientes con esquizofrenia manifestaron un deterioro significativo del recuerdo dependiente del contexto de la memoria de extinción. Además, en ellos la gravedad del delirio se correlacionó con los niveles de conductancia cutánea basal. Conclusiones: Los datos del presente estudio coinciden con las pruebas obtenidas en investigaciones previas de una mayor respuesta neural a los estímulos inocuos en la esquizofrenia y niveles de vigilia elevados en la psicosis. El hallazgo de un recuerdo deficiente de la extinción en pacientes con esquizofrenia que manifestaron un aprendizaje intacto de ella sugiere que la enfermedad se asocia con una alteración de los procesos neurales, que son la base de la memoria emocional (AU)

Background: Schizophrenia is associated with abnormalities in emotional processing and social cognition, which might result from disruption of the underlying neural mechanism(s) governing emotional learning and memory. To investigate this possibility, we measured the acquisition and extinction of conditioned fear responses and delayed recall of extinction in schizophrenia and control subjects. Methods: Twenty-eight schizophrenia and 18 demographically matched control subjects underwent a 2-day fear conditioning, extinction learning, and extinction recall procedure, in which skin conductance response (SCR) magnitude was used as the index of conditioned responses. Results: During fear acquisition, 83% of the control subjects and 57% of the patients showed autonomic responsivity (“responders”), and the patients showed larger SCRs to the stimulus that was not paired with the unconditioned stimulus (CS_) than the control subjects. Within the responder group, there was no difference between the patients and control subjects in levels of extinction learning; however, the schizophrenia patients showed significant impairment, relative to the control subjects, in context-dependent recall of the extinction memory. In addition, delusion severity in the patients correlated with baseline skin conductance levels. Conclusions: These data are consistent with prior evidence for a heightened neural response to innocuous stimuli in schizophrenia and elevated arousal levels in psychosis. The finding of deficient extinction recall in schizophrenia patients who showed intact extinction learning suggests that schizophrenia is associated with a disturbance in the neural processes supporting emotional memory (AU)

Extinction memory is impaired in schizophrenia.

BACKGROUND: Schizophrenia is associated with abnormalities in emotional processing and social cognition, which might result from disruption of the underlying neural mechanism(s) governing emotional learning and memory. To investigate this possibility, we measured the acquisition and extinction of conditioned fear responses and delayed recall of extinction in schizophrenia and control subjects. METHODS: Twenty-eight schizophrenia and 18 demographically matched control subjects underwent a 2-day fear conditioning, extinction learning, and extinction recall procedure, in which skin conductance response (SCR) magnitude was used as the index of conditioned responses. RESULTS: During fear acquisition, 83% of the control subjects and 57% of the patients showed autonomic responsivity ("responders"), and the patients showed larger SCRs to the stimulus that was not paired with the unconditioned stimulus (CS-) than the control subjects. Within the responder group, there was no difference between the patients and control subjects in levels of extinction learning; however, the schizophrenia patients showed significant impairment, relative to the control subjects, in context-dependent recall of the extinction memory. In addition, delusion severity in the patients correlated with baseline skin conductance levels. CONCLUSIONS: These data are consistent with prior evidence for a heightened neural response to innocuous stimuli in schizophrenia and elevated arousal levels in psychosis. The finding of deficient extinction recall in schizophrenia patients who showed intact extinction learning suggests that schizophrenia is associated with a disturbance in the neural processes supporting emotional memory.

Inactivation of the ventromedial prefrontal cortex reduces expression of conditioned fear and impairs subsequent recall of extinction.

Anxiety disorders are thought to reflect deficits in the regulation of fear expression. Evidence from rodent studies implicates the ventromedial prefrontal cortex (vmPFC) in the regulation of conditioned fear. Lesions of the vmPFC have had differing effects on the acquisition and expression of conditioned fear, as well as on recall of extinction. The use of permanent lesions, however, makes it difficult to assess the phase of training in which the vmPFC is acting and can trigger recruitment of other structures, thereby masking lesion deficits. To overcome these problems, we temporarily inactivated the vmPFC of rats with tetrodotoxin (10 ng in a 0.5-microl midline infusion) at one of four time points: prior to conditioning, prior to extinction, immediately after extinction or prior to recall of extinction. Consistent with lesion findings, inactivation of the vmPFC prior to acquisition had no effect but inactivation prior to extinction led to impaired recall of extinction the following day. In contrast to lesion findings, inactivation of the vmPFC decreased freezing at all time points, suggesting that some component of the vmPFC facilitates the expression of conditioned fear. These findings suggest that inactivation of the vmPFC can have opposite effects depending on the phase of training. The vmPFC appears to be involved both in stimulating the expression of conditioned fear and in serving as a site of extinction-related plasticity that inhibits fear during recall of extinction.