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1.  Extinction of Conditioned Fear is Better Learned and Recalled in the Morning than in the Evening 
Journal of psychiatric research  2013;47(11):1776-1784.
Sleep helps emotional memories consolidate and may promote generalization of fear extinction memory. We examined whether extinction learning and memory might differ in the morning and evening due, potentially, to circadian and/or sleep-homeostatic factors. Healthy men (N=109) in 6 groups completed a 2-session protocol. In Session 1, fear conditioning was followed by extinction learning. Partial reinforcement with mild electric shock produced conditioned skin conductance responses (SCR) to 2 differently colored lamps (CS+), but not a third color (CS−), within the computer image of a room (conditioning context). One CS+ (CS+E) but not the other (CS+U) was immediately extinguished by un-reinforced presentations in a different room (extinction context). Delay durations of 3 hr (within AM or PM), 12 hr (morning-to-evening or evening-to-morning) or 24 hr (morning-to-morning or evening-to-evening) followed. In Session 2, extinction recall and contextual fear renewal were tested. We observed no significant effects of the delay interval on extinction memory but did observe an effect of time-of-day. Fear extinction was significantly better if learned in the morning (p=.002). Collapsing across CS+ type, there was smaller morning differential SCR at both extinction recall (p=.003) and fear renewal (p=.005). Morning extinction recall showed better generalization from the CS+E to CS+U with the response to the CS+U significantly larger than to the CS+E only in the evening (p=.028). Thus, extinction is learned faster and its memory is better generalized in the morning. Cortisol and testosterone showed the expected greater salivary levels in the morning when higher testosterone/cortisol ratio also predicting better extinction learning. Circadian factors may promote morning extinction. Alternatively, evening homeostatic sleep pressure may impede extinction and favor recall of conditioned fear.
PMCID: PMC3791331  PMID: 23992769
Sleep; fear conditioning; extinction; circadian rhythm; sleep homeostasis; cortisol; testosterone
2.  Trauma Reactivation Plus Propranolol Is Associated With Durably Low Physiological Responding During Subsequent Script-Driven Traumatic Imagery 
In a previous, double-blind, placebo-controlled study, patients with posttraumatic stress disorder (PTSD) showed lower physiological response during script-driven traumatic imagery 1 week after receiving a single dose of propranolol given after the retrieval of a traumatic memory. We hypothesized that this effect would extend beyond 1 week using a modified treatment approach.
Twenty-eight participants with PTSD read an account of their traumatic event once weekly for 6 consecutive weeks under the influence of open-label propranolol. One week and 4-months later, skin conductance, heart rate, and left corrugator electromyogram responses were measured while participants engaged in script-driven mental imagery of their traumatic event. Results from the 22 study participants were compared with results from treated and untreated participants in a previously published trial.
Most participants in our study were classified as non-PTSD cases at posttreatment and follow-up according to a psychophysiological discriminant function analysis. Posttreatment skin conductance and heart rate responses of the current (propranolol-treated) participants were lower than those of placebo participants from the previous study. No difference was observed between physiological responding measured posttreatment and at follow-up.
Low physiological responding during script-driven traumatic imagery after treatment extends up to 4 months, demonstrating the durability of the treatment effect’s. Limitations include the absence of a placebo-controlled group and lack of physiological baseline measures. Despite these limitations, results point to the need for future trials examining the clinical efficacy of trauma reactivation plus propranolol, as it has the potential to become a novel, cost- and time-effective treatment for PTSD.
PMCID: PMC4079131  PMID: 25007116
posttraumatic stress disorder; treatment; reconsolidation; memory; propranolol; traumatic stress
3.  Resting amygdala and medial prefrontal metabolism predicts functional activation of the fear extinction circuit 
The American journal of psychiatry  2012;169(4):415-423.
Individual differences in ability to control fear have been linked to activation of dorsal anterior cingulate cortex, ventromedial prefrontal cortex, and amygdala. This study investigated whether functional variance in this network can be predicted by resting metabolism in these same regions.
Healthy subject volunteers were studied with positron emission tomography using [18F]-deoxyglucose to measure resting brain metabolism. This was followed by a two-day fear conditioning and extinction training paradigm in a functional magnetic resonance imaging scanner to measure brain activation during fear extinction and its recall. Skin conductance response was used to index conditioned responding. Resting metabolism in amygdala, dorsal anterior cingulate cortex and ventromedial prefrontal cortex were used to predict responses during fear extinction and extinction recall.
During extinction training, resting amygdala metabolism positively predicted ventromedial prefrontal cortex, and negatively predicted dorsal anterior cingulate cortex, activation. In contrast, during extinction recall, resting amygdala metabolism negatively predicted ventromedial prefrontal cortex, and positively predicted dorsal anterior cingulate cortex, activation. Resting dorsal anterior cingulate cortex metabolism predicted fear expression (skin conductance response) during extinction recall.
Brain metabolism at rest predicts neuronal reactivity and skin conductance changes associated with recall of the fear extinction memory.
PMCID: PMC4080711  PMID: 22318762
4.  Preclinical Evaluation of Reconsolidation Blockade by Clonidine as a Potential Novel Treatment for Posttraumatic Stress Disorder 
Neuropsychopharmacology  2012;37(13):2789-2796.
Exposure to traumatic events can lead to posttraumatic stress disorder (PTSD). Current PTSD treatments typically only produce partial improvement. Hence, there is a need for preclinical research to identify new candidate drugs and to develop novel therapeutic approaches. Animal studies have indicated that fear memories can be weakened by blocking restabilization after retrieval, a process known as reconsolidation. Furthermore, evidence suggests that there are important alterations of the noradrenergic system in PTSD, and hence it may be of interest to study drugs that target this pathway. Here, we investigated the efficacy of clonidine, an α2-adrenoreceptor agonist, to block reconsolidation in an animal model of persistent traumatic memories. Using an auditory fear conditioning paradigm in rats, we tested the efficacy of clonidine to weaken fear memory retention when administered systemically after retrieval. We evaluated dosage, number of treatments, and specificity in reconsolidation blockade. We found that postretrieval administration of clonidine disrupts fear-related memories in a dose-dependent manner and that two treatments are sufficient for maximal memory impairment. Furthermore, we determined that this effect is long lasting and specific to reconsolidation processes as shown by the selectivity to affect reactivated memories and the absence of spontaneous recovery and of postreactivation short-term memory impairment. Our results demonstrate the efficacy of systemic administration of clonidine following retrieval to persistently disrupt fear memory retention through reconsolidation blockade. This study provides important preclinical parameters for future therapeutic strategies involving clonidine to block reconsolidation as a novel treatment for PTSD symptoms.
PMCID: PMC3499710  PMID: 22871915
clonidine; memory; reconsolidation; fear conditioning; α2-adrenoreceptor agonist; posttraumatic stress disorder; psychopharmacology; psychiatry & behavioral sciences; mood/anxiety/stress disorders; learning & memory; reconsolidation; a2-adrenoreceptor agonist; fear conditioning; posttraumatic stress disorder; clonidine
5.  Cavum Septum Pellucidum in Monozygotic Twins Discordant for Combat Exposure: Relationship to Posttraumatic Stress Disorder 
Biological psychiatry  2004;55(6):656-658.
Abnormally large cavum septum pellucidum has been reported in posttraumatic stress disorder; however, the origin of this association is uncertain.
We utilized magnetic resonance imaging to measure cavum septum pellucidum in pairs of identical twins discordant for combat exposure in Vietnam.
Presence of abnormal cavum septum pellucidum was significantly correlated between exposed and unexposed twins, indicating that it is partially determined by heredity and/or shared environment. There was a greater proportion of cavum septum pellucidum in combat-exposed twins with posttraumatic stress disorder and their noncombat-exposed co-twins.
The presence of abnormally large cavum septum pellucidum is a familial vulnerability factor for posttraumatic stress disorder.
PMCID: PMC2794416  PMID: 15013837
Septum pellucidum; stress disorders; posttraumatic; magnetic resonance imaging; twins; monozygotic
6.  Event-Related Potentials to Auditory Stimuli in Monozygotic Twins Discordant for Combat: Association with PTSD 
Psychophysiology  2008;46(1):10.1111/j.1469-8986.2008.00720.x.
Studies have demonstrated ERP abnormalities related to concentration difficulties in post-traumatic stress disorder (PTSD). We used an identical-twin, case-control design to investigate whether these abnormalities reflect pre-trauma vulnerability or the acquired consequence of PTSD. Vietnam combat veterans and their non-combat-exposed, identical twins completed a three-tone oddball task. Veterans with PTSD had delayed target N2 latencies compared to veterans without PTSD. In a small non-medicated, non-smoking subsample, veterans with PTSD also had significantly diminished target P3b amplitudes. A mixed-model, random-effects analysis on the non-medicated, non-smoking subsample that included the combat-unexposed co-twins showed a significant Diagnosis × combat Exposure interaction for target P3b amplitude. Results replicate increased N2 latency and diminished P3b amplitude in PTSD and suggest that diminished P3b amplitude is an acquired condition in PTSD.
PMCID: PMC3807820  PMID: 18803598
Twin studies; Posttraumatic stress disorder; Event-related potentials; P3b
7.  Clarifying the Origin of Biological Abnormalities in PTSD Through the Study of Identical Twins Discordant for Combat Exposure 
A biological abnormality found to be associated with post-traumatic stress disorder (PTSD) may be, among other things, a pre-trauma vulnerability factor, that is, it may have been present prior to the event’s occurrence and increased the individual’s likelihood of developing PTSD upon traumatic exposure. Alternately, it may be an acquired PTSD sign, that is, it may have developed after the traumatic exposure, along with the PTSD. We have studied pairs of Vietnam combat veterans and their noncombat-exposed, identical twins in an effort to resolve these competing origins. Combat veterans were diagnosed as current PTSD or non-PTSD (i.e., never had). Average heart rate responses (HRRs) to a series of sudden, loud-tone presentations were larger in Vietnam combat veteran twins with PTSD, but these larger responses were not shared by their noncombat-exposed cotwins, whose responses were similar to those of the non-PTSD combat veterans and their noncombat-exposed cotwins. These results suggest that larger HRRs to sudden, loud tones represent an acquired sign of PTSD. In contrast, increased neurological soft signs (NSSs), diminished hippocampal volume, and presence of abnormal cavum septum pellucidum (CSP) were found in Vietnam combat veteran twins with PTSD and their “high-risk,” unexposed cotwins compared to Vietnam combat veteran twins without PTSD and their “low-risk,” unexposed cotwins. These results support the conclusion that the latter abnormalities represent antecedent, familial vulnerability factors for developing chronic PTSD upon exposure to a traumatic event.
PMCID: PMC2770249  PMID: 16891575
stress disorders; posttraumatic; twins; monozygotic; startle response; neurological examination; magnetic resonance imaging; hippocampus; septum pellucidum
8.  Exaggerated Activation of Dorsal Anterior Cingulate Cortex During Cognitive Interference: A Monozygotic Twin Study of Posttraumatic Stress Disorder 
The American journal of psychiatry  2011;168(9):979-985.
Neuroimaging studies have revealed functional abnormalities in the anterior cingulate cortex in posttraumatic stress disorder (PTSD). The goal of the current research was to determine whether hyperresponsivity of the dorsal anterior cingulate in PTSD is an acquired characteristic or familial risk factor.
Using a case-control twin design, we studied combat-exposed veterans with PTSD (n=12) and their identical combat-unexposed co-twins (n=12), as well as combat-exposed veterans without PTSD (n=14) and their identical combat-unexposed co-twins (n=14). Participants underwent functional magnetic resonance imaging during completion of the Multi-Source Interference Task, which reliably activates the dorsal anterior cingulate.
Combat veterans with PTSD and their co-twins had significantly greater activation in the dorsal anterior cingulate and tended to have larger response time difference scores, as compared to non-PTSD veterans and their co-twins. Dorsal anterior cingulate activation in the exposed twins was positively correlated with their PTSD symptom severity. Dorsal anterior cingulate activation in the unexposed twins was positively correlated with their combat-exposed co-twins’ PTSD symptom severity, but not with depression or alcohol use severity in the combat-exposed co-twins.
Hyperresponsivity in the dorsal anterior cingulate appears to be a familial risk factor for the development of PTSD following psychological trauma.
PMCID: PMC3773363  PMID: 21724666
magnetic resonance imaging; limbic system; stress disorders; post-traumatic; twins; monozygotic; gyrus cinguli; Multi-Source Interference Task
9.  Resting Metabolic Activity in the Cingulate Cortex and Vulnerability to Posttraumatic Stress Disorder 
Archives of general psychiatry  2009;66(10):1099-1107.
Recent neuroimaging research has revealed functional abnormalities in the anterior cingulate cortex, amygdala and hippocampus in posttraumatic stress disorder (PTSD).
To determine whether resting functional abnormalities found in PTSD are acquired characteristics or familial risk factors.
Cross-sectional design including identical twins discordant for trauma exposure.
Academic medical center.
Combat-exposed veterans with PTSD (n=14) and their identical, combat-unexposed co-twins (n=14), as well as combat-exposed veterans without PTSD (n=19) and their identical, combat-unexposed co-twins (n=19).
Main Outcome Measures
We used positron emission tomography and [18F]-fluorodeoxyglucose to examine resting regional cerebral metabolic rates for glucose (rCMRglu).
Veterans with PTSD and their co-twins had significantly higher resting rCMRglu in dorsal anterior cingulate/mid cingulate cortex (dACC/MCC) compared to non-PTSD veterans and their co-twins. Resting rCMRglu in dACC/MCC in the combat-unexposed co-twins was positively correlated with combat exposure severity, PTSD symptom severity, and alcohol use in their exposed twins.
Enhanced resting metabolic activity in dACC/MCC appears to represent a familial risk factor for developing PTSD after exposure to psychological trauma.
PMCID: PMC3752096  PMID: 19805700
stress disorders; post-traumatic; twins; monozygotic; positron-emission tomography; fluorodexoyglucose F18; metabolism; cingulate gyrus
10.  Extinction memory is impaired in schizophrenia 
Biological psychiatry  2008;65(6):455-463.
Schizophrenia is associated with abnormalities in emotional processing and social cognition, which may 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.
28 schizophrenia and 18 demographically-matched control subjects underwent a two-day fear conditioning, extinction learning and extinction recall procedure, in which skin conductance response (SCR) magnitude was used as the index of conditioned responses.
During fear acquisition, 83% of the controls 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 controls. Within the responder group, there was no difference between the patients and controls in levels of extinction learning; however, the schizophrenia patients showed significant impairment, relative to the controls, in context-dependent recall of the extinction memory. In addition, delusion severity in the patients correlated with baseline skin conductance levels.
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.
PMCID: PMC3740529  PMID: 18986648
schizophrenia; fear; conditioning; extinction; emotion; memory
11.  Propranolol’s effects on the consolidation and reconsolidation of long-term emotional memory in healthy participants: a meta-analysis 
Considering the pivotal role of negative emotional experiences in the development and persistence of mental disorders, interfering with the consolidation/reconsolidation of such experiences would open the door to a novel treatment approach in psychiatry. We conducted a meta-analysis on the experimental evidence regarding the capacity of the β-blocker propranolol to block the consolidation/reconsolidation of emotional memories in healthy adults.
Selected studies consisted of randomized, double-blind experiments assessing long-term memory for emotional material in healthy adults and involved at least 1 propranolol and 1 placebo condition. We searched PsycInfo, PubMed, Web of Science, Cochrane Central, PILOTS, Google Scholar and for eligible studies from the period 1995–2012. Ten consolidation (n = 259) and 8 reconsolidation (n = 308) experiments met the inclusion criteria. We calculated effect sizes (Hedges g) using a random effects model.
Compared with placebo, propranolol given before memory consolidation reduced subsequent recall for negatively valenced stories, pictures and word lists (Hedges g = 0.44, 95% confidence interval [CI] 0.14–0.74). Propranolol before reconsolidation also reduced subsequent recall for negatively valenced emotional words and the expression of cue-elicited fear responses (Hedges g = 0.56, 95% CI 0.13–1.00).
Limitations include the moderate number of studies examining the influence of propranolol on emotional memory consolidation and reconsolidation in healthy adults and the fact that most samples consisted entirely of young adults, which may limit the ecological validity of results.
Propranolol shows promise in reducing subsequent memory for new or recalled emotional material in healthy adults. However, future studies will need to investigate whether more powerful idiosyncratic emotional memories can also be weakened and whether this weakening can bring about long-lasting symptomatic relief in clinical populations, such as patients with posttraumatic stress or other event-related disorders.
PMCID: PMC3692719  PMID: 23182304
12.  Neurological Soft Signs in Individuals with Pathological Gambling 
PLoS ONE  2013;8(4):e60885.
Increased neurological soft signs (NSSs) have been found in a number of neuropsychiatric syndromes, including chemical addiction. The present study examined NSSs related to perceptual-motor and visuospatial processing in a behavioral addiction viz., pathological gambling (PG). As compared to mentally healthy individuals, pathological gamblers displayed significantly poorer ability to copy two- and three-dimensional figures, to recognize objects against a background noise, and to orient in space on a road-map test. Results indicated that PG is associated with subtle cerebral cortical abnormalities. Further prospective clinical research is needed to address the NSSs' origin and chronology (e.g., predate or follow the development of PG) as well as their response to therapeutic interventions and/or their ability to predict such a response.
PMCID: PMC3617209  PMID: 23593341
13.  Resting cerebral metabolism correlates with skin conductance and functional brain activation during fear conditioning 
Biological Psychology  2011;89(2):450-459.
We investigated whether resting brain metabolism can be used to predict autonomic and neuronal responses during fear conditioning in 20 healthy humans. Regional cerebral metabolic rate for glucose was measured via positron emission tomography at rest. During conditioning, autonomic responses were measured via skin conductance, and blood oxygen level dependent signal was measured via functional magnetic resonance imaging. Resting dorsal anterior cingulate metabolism positively predicted differentially conditioned skin conductance responses. Midbrain and insula resting metabolism negatively predicted midbrain and insula functional reactivity, while dorsal anterior cingulate resting metabolism positively predicted midbrain functional reactivity. We conclude that resting metabolism in limbic areas can predict some aspects of psychophysiological and neuronal reactivity during fear learning.
PMCID: PMC3269527  PMID: 22207247
14.  The relationship between Hippocampal asymmetry and working memory processing in combat-related PTSD – a monozygotic twin study 
PTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. Hippocampal asymmetry has received less attention, but potentially could indicate lateralised differences in vulnerability to trauma. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD.
Our study examined hippocampal volume asymmetry and the relationship between hippocampal asymmetry and P300 amplitude in male monozygotic twins discordant for Vietnam combat exposure. Lateralised hippocampal volume and P300 data were obtained from 70 male participants, of whom 12 had PTSD. We were able to compare (1) combat veterans with current PTSD; (2) their non-combat-exposed co-twins; (3) combat veterans without current PTSD and (4) their non-combat-exposed co-twins.
There were no significant differences between groups in hippocampal asymmetry. There were no group differences in performance of an auditory oddball target detection task or in P300 amplitude. There was a significant positive correlation between P300 amplitude and the magnitude of hippocampal asymmetry in participants with PTSD.
These findings suggest that greater hippocampal asymmetry in PTSD is associated with a need to allocate more attentional resources when processing significant environmental stimuli.
PMCID: PMC3582553  PMID: 23198722
15.  Predicting post-trauma stress symptoms from pre-trauma psychophysiologic reactivity, personality traits and measures of psychopathology 
Most individuals exposed to a traumatic event do not develop post-traumatic stress disorder (PTSD), although many individuals may experience sub-clinical levels of post-traumatic stress symptoms (PTSS). There are notable individual differences in the presence and severity of PTSS among individuals who report seemingly comparable traumatic events. Individual differences in PTSS following exposure to traumatic events could be influenced by pre-trauma vulnerabilities for developing PTSS/PTSD.
Pre-trauma psychological, psychophysiological and personality variables were prospectively assessed for their predictive relationships with post-traumatic stress symptoms (PTSS). Police and firefighter trainees were tested at the start of their professional training (i.e., pre-trauma; n = 211) and again several months after exposure to a potentially traumatic event (i.e., post-trauma, n = 99). Pre-trauma assessments included diagnostic interviews, psychological and personality measures and two psychophysiological assessment procedures. The psychophysiological assessments measured psychophysiologic reactivity to loud tones and the acquisition and extinction of a conditioned fear response. Post-trauma assessment included a measure of psychophysiologic reactivity during recollection of the traumatic event using a script-driven imagery task.
Logistic stepwise regression identified the combination of lower IQ, higher depression score and poorer extinction of forehead (corrugator) electromyogram responses as pre-trauma predictors of higher PTSS. The combination of lower IQ and increased skin conductance (SC) reactivity to loud tones were identified as pre-trauma predictors of higher post-trauma psychophysiologic reactivity during recollection of the traumatic event. A univariate relationship was also observed between pre-trauma heart rate (HR) reactivity to fear cues during conditioning and post-trauma psychophysiologic reactivity.
The current study contributes to a very limited literature reporting results from truly prospective examinations of pre-trauma physiologic, psychologic, and demographic predictors of PTSS. Findings that combinations of lower estimated IQ, greater depression symptoms, a larger differential corrugator EMG response during extinction and larger SC responses to loud tones significantly predicted higher PTSS suggests that the process(es) underlying these traits contribute to the pathogenesis of subjective and physiological PTSS. Due to the low levels of PTSS severity and relatively restricted ranges of outcome scores due to the healthy nature of the participants, results may underestimate actual predictive relationships.
PMCID: PMC3412748  PMID: 22738068
Stress disorders, Post-traumatic; Conditioning; Startle; Imagery; Psychophysiology; Risk factors
16.  An fMRI study of unconditioned responses in post-traumatic stress disorder 
Both fear and pain processing are altered in post-traumatic stress disorder (PTSD), as evidenced by functional neuroimaging studies showing increased amygdala responses to threats, and increased insula, putamen and caudate activity in response to heat pain. Using psychophysiology and functional magnetic resonance imaging, we studied conditioned and unconditioned autonomic and neuronal responses in subjects with PTSD versus trauma-exposed non-PTSD control (TENC) subjects. A design using an electric shock selected by subjects to be 'highly annoying but not painful' as an unconditioned stimulus (US) with partially reinforced cues allowed us to partly disentangle the expectancy- and prediction-error components from sensory components of the unconditioned response.
Whereas responses to the conditioned stimulus (CS) were similar in PTSD and TENC, the former displayed higher putamen, insula, caudate and amygdala responses to the US. Reactivity to the US in the anterior insula correlated with PTSD symptom severity. Functional connectivity analyses using the putamen as a seed region indicated that TENC subjects had increased amygdala-putamen connectivity during US delivery; this connection was disengaged in PTSD.
Our results indicate that although neural processing of fear learning in people with PTSD seems to be comparable with controls, neural responses to unconditioned aversive stimuli in PTSD seem to be increased.
PMCID: PMC3384234  PMID: 22738227
17.  The influence of gonadal hormones on conditioned fear extinction in healthy humans 
Neuroscience  2010;168(3):652-658.
Recent rodent studies suggest that gonadal hormones influence extinction of conditioned fear. Here we investigated sex differences in, and the influence of estradiol and progesterone on, fear extinction in healthy humans. Men and women underwent a two-day paradigm in which fear conditioning and extinction learning took place on day 1 and extinction recall was tested on day 2. Visual cues were used as the conditioned stimuli and a mild electric shock was used as the unconditioned stimulus. Skin conductance was recorded throughout the experiment and used to measure conditioned responses (CRs). Blood samples were obtained from all women to measure estradiol and progesterone levels. We found that higher estradiol during extinction learning enhanced subsequent extinction recall but had no effects on fear acquisition or extinction learning itself. Sex differences were only observed during acquisition, with men exhibiting significantly higher CRs. After dividing women into low- and high-estradiol groups, men showed comparable extinction recall to high-estradiol women, and both of these groups showed higher extinction recall than low-estradiol women. Therefore, sex differences in extinction memory emerged only after taking into account women's estradiol levels. Lower estradiol may impair extinction consolidation in women. These findings could have practical applications in the treatment of anxiety disorders through cognitive and behavioral therapies.
PMCID: PMC2881679  PMID: 20412837
estrogen; progesterone; sex difference; fear; menstrual cycle; learning and memory
18.  Stress reduction correlates with structural changes in the amygdala 
Stress has significant adverse effects on health and is a risk factor for many illnesses. Neurobiological studies have implicated the amygdala as a brain structure crucial in stress responses. Whereas hyperactive amygdala function is often observed during stress conditions, cross-sectional reports of differences in gray matter structure have been less consistent. We conducted a longitudinal MRI study to investigate the relationship between changes in perceived stress with changes in amygdala gray matter density following a stress-reduction intervention. Stressed but otherwise healthy individuals (N = 26) participated in an 8-week mindfulness-based stress reduction intervention. Perceived stress was rated on the perceived stress scale (PSS) and anatomical MR images were acquired pre- and post-intervention. PSS change was used as the predictive regressor for changes in gray matter density within the bilateral amygdalae. Following the intervention, participants reported significantly reduced perceived stress. Reductions in perceived stress correlated positively with decreases in right basolateral amygdala gray matter density. Whereas prior studies found gray matter modifications resulting from acquisition of abstract information, motor and language skills, this study demonstrates that neuroplastic changes are associated with improvements in a psychological state variable.
PMCID: PMC2840837  PMID: 19776221
stress; amygdala; gray matter; MRI; mindfulness
21.  Neurobiological Basis of Failure to Recall Extinction Memory in Posttraumatic Stress Disorder 
Biological psychiatry  2009;66(12):1075-1082.
A clinical characteristic of posttraumatic stress disorder (PTSD) is persistently elevated fear responses to stimuli associated with the traumatic event. The objective herein is to determine whether extinction of fear responses is impaired in PTSD and whether such impairment is related to dysfunctional activation of brain regions known to be involved in fear extinction, viz., amygdala, hippocampus, ventromedial prefrontal cortex (vmPFC), and dorsal anterior cingulate cortex (dACC).
Sixteen individuals diagnosed with PTSD and 15 trauma-exposed non-PTSD controls (TENCs) underwent a two-day fear conditioning and extinction protocol in a 3T fMRI scanner. Conditioning and extinction training were conducted on day 1. Extinction recall (or extinction memory) test was conducted on day 2 (extinguished conditioned stimuli presented in the absence of shock). Skin conductance response (SCR) was scored throughout the experiment as an index of the conditioned response.
SCR data revealed no significant differences between groups during acquisition and extinction of conditioned fear on day 1. On day 2, however, PTSD subjects showed impaired recall of extinction memory. Analysis of fMRI data showed greater amygdala activation in the PTSD group during day 1 extinction learning. During extinction recall, lesser activation in hippocampus and vmPFC, and greater activation in dACC, was observed in the PTSD group. The magnitude of extinction memory across all subjects was correlated with activation of hippocampus and vmPFC during extinction recall testing.
These findings support the hypothesis that fear extinction is impaired in PTSD. They further suggest that dysfunctional activation in brain structures that mediate fear extinction learning, and especially its recall, underlie this impairment.
PMCID: PMC2787650  PMID: 19748076
conditioning, classical; stress disorders, post-traumatic; magnetic resonance imaging; amygdala; hippocampus; prefrontal cortex
22.  Magnetic Resonance Imaging Study of Hippocampal Volume in Chronic, Combat-Related Posttraumatic Stress Disorder 
Biological psychiatry  1996;40(11):1091-1099.
This study used quantitative volumetric magnetic resonance imaging techniques to explore the neuroanatomic correlates of chronic, combat-related posttraumatic stress disorder (PTSD) in seven Vietnam veterans with PTSD compared with seven nonPTSD combat veterans and eight normal nonveterans. Both left and right hippocampi were significantly smaller in the PTSD subjects compared to the Combat Control and Normal subjects, even after adjusting for age, whole brain volume, and lifetime alcohol consumption. There were no statistically significant group differences in intracranial cavity, whole brain, ventricles, ventricle:brain ratio, or amygdala. Subarachnoidal cerebrospinal fluid was increased in both veteran groups. Our finding of decreased hippocampal volume in PTSD subjects is consistent with results of other investigations which utilized only trauma-unexposed control groups. Hippocampal volume was directly correlated with combat exposure, which suggests that traumatic stress may damage the hippocampus. Alternatively, smaller hippocampi volume may be a pre-existing risk factor for combat exposure and/or the development of PTSD upon combat exposure.
PMCID: PMC2910907  PMID: 8931911
Stress disorders; posttraumatic; magnetic resonance imaging; hippocampus
23.  Intensity dependence of auditory P2 in monozygotic twins discordant for Vietnam combat: Associations with posttraumatic stress disorder 
Two studies have reported decreased intensity dependence of the P2 event-related potential (ERP) in male combat veterans with posttraumatic stress disorder (PTSD), a response pattern presumed to reflect central nervous system-induced protective inhibition and heightened central serotonergic activity. We used an identical twin, case-control design to investigate whether intensity dependence abnormalities reflect pretrauma vulnerability or are an acquired consequence of PTSD. ERPs were measured in male Vietnam combat veterans and their noncombat-exposed monozygotic twin brothers during a four-tone, stimulus-intensity modulation procedure. Contrary to previous findings in male veterans, the PTSD group had significantly steeper P2 amplitude intensity slopes, similar to those reported for female veterans and abused children with PTSD. Additionally, increased P2 amplitude intensity slope was associated with increased PTSD symptom severity, particularly the severity of reexperiencing symptoms. A mixed-model, random-effects analysis that included the combat-unexposed twins revealed a significant diagnosis by combat exposure interaction. Inspection of group means suggests that the observed increased P2 intensity dependence is a consequence of PTSD. Our findings further suggest that low serotonergic tone may emerge as one potential consequence of this disorder.
PMCID: PMC2861279  PMID: 18629752
5-HT; auditory intensity dependence; combat disorder; event-related potentials; posttraumatic; PTSD; rehabilitation; serotonin; stress disorders; twin studies
24.  Longitudinal MRI Study of Hippocampal Volume in Trauma Survivors With PTSD 
The authors prospectively explored whether a reduction in the volume of the hippocampus occurs in recent trauma survivors who develop posttraumatic stress disorder (PTSD).
Thirty-seven survivors of traumatic events were assessed within a week of the traumatic event and 6 months later. The assessment included magnetic resonance imaging of the brain (including 124 coronal slices of 1.5-mm thickness), psychometric testing, and structured clinical interviews. The Clinician-Administered PTSD Scale conferred PTSD diagnoses at 6 months.
Ten subjects (27%) had PTSD at 6 months. The subjects with PTSD did not differ from those without PTSD in hippocampal volume (right or left) at 1 week or 6 months. There was no reduction in hippocampal volume in the PTSD subjects between 1 week and 6 months.
Smaller hippocampal volume is not a necessary risk factor for developing PTSD and does not occur within 6 months of expressing the disorder. This brain abnormality might occur in individuals with chronic or complicated PTSD.
PMCID: PMC2819102  PMID: 11481158
25.  Smaller hippocampal volume predicts pathologic vulnerability to psychological trauma 
Nature neuroscience  2002;5(11):1242-1247.
In animals, exposure to severe stress can damage the hippocampus. Recent human studies show smaller hippocampal volume in individuals with the stress-related psychiatric condition posttraumatic stress disorder (PTSD). Does this represent the neurotoxic effect of trauma, or is smaller hippocampal volume a pre-existing condition that renders the brain more vulnerable to the development of pathological stress responses? In monozygotic twins discordant for trauma exposure, we found evidence that smaller hippocampi indeed constitute a risk factor for the development of stress-related psychopathology. Disorder severity in PTSD patients who were exposed to trauma was negatively correlated with the hippocampal volume of both the patients and the patients’ trauma-unexposed identical co-twin. Furthermore, severe PTSD twin pairs—both the trauma-exposed and unexposed members—had significantly smaller hippocampi than non-PTSD pairs.
PMCID: PMC2819093  PMID: 12379862

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