Erin Falconer

Dissociative responses to conscious and non-conscious fear impact underlying brain function in post-traumatic stress disorder

BACKGROUND Dissociative reactions in post-traumatic stress disorder (PTSD) have been regarded as strategic responses that limit arousal. Neuroimaging studies suggest distinct prefrontal responses in individuals displaying dissociative and hyperarousal responses to threat in PTSD. Increased prefrontal activity may reflect enhanced regulation of limbic arousal networks in dissociation. If dissociation is a higher-order regulatory response to threat, there may be differential responses to conscious and automatic processing of threat stimuli. This study addresses this question by examining the impact of dissociation on fear processing at different levels of awareness. METHOD Functional magnetic resonance imaging (fMRI) with a 1.5-T scanner was used to examine activation to fearful (versus neutral) facial expressions during consciously attended and non-conscious (using backward masking) conditions in 23 individuals with PTSD. Activation in 11 individuals displaying non-dissociative reactions was compared to activation in 12 displaying dissociative reactions to consciously and non-consciously perceived fear stimuli. RESULTS Dissociative PTSD was associated with enhanced activation in the ventral prefrontal cortex for conscious fear, and in the bilateral amygdala, insula and left thalamus for non-conscious fear compared to non-dissociative PTSD. Comparatively reduced activation in the dissociative group was apparent in dorsomedial prefrontal regions for conscious fear faces. CONCLUSIONS These findings confirm our hypotheses of enhanced prefrontal activity to conscious fear and enhanced activity in limbic networks to non-conscious fear in dissociative PTSD. This supports the theory that dissociation is a regulatory strategy invoked to cope with extreme arousal in PTSD, but this strategy appears to function only during conscious processing of threat.

Neural Responses to Masked Fear Faces: Sex Differences and Trauma Exposure in Posttraumatic Stress Disorder

Although women have a greater propensity than men to develop posttraumatic stress disorder (PTSD) following trauma, sex differences in neural activations to threat have received little investigation. This study tested the prediction that trauma would heighten activity in automatic fear-processing networks to a greater extent in women than in men. Functional magnetic resonance imaging (fMRI) data were recorded in 23 participants with PTSD (13 women, 10 men), 21 trauma-exposed controls (9 women, 12 men), and 42 non-trauma-exposed controls (22 women, 20 men) while they viewed masked facial expressions of fear. Exposure to trauma was associated with enhanced brainstem activity to fear in women, regardless of the presence of PTSD, but in men, it was associated only with the development of PTSD. Men with PTSD displayed greater hippocampal activity to fear than did women. Both men and women with PTSD showed enhanced amygdala activity to fear relative to controls. The authors conclude that greater brainstem activation to threat stimuli may contribute to the greater prevalence of PTSD in women, and greater hippocampal activation in men may subserve an enhanced capacity for contextualizing fear-related stimuli.

Preliminary Evidence of the Short Allele of the Serotonin Transporter Gene Predicting Poor Response to Cognitive Behavior Therapy in Posttraumatic Stress Disorder

OBJECTIVE This study was intended to assess the extent to which the low-expression alleles of the serotonin transporter gene promoter predict poor response to cognitive behavior therapy in patients with posttraumatic stress disorder (PTSD). METHOD Forty-five patients with PTSD underwent an 8-week exposure-based cognitive behavior therapy program and provided mouth swabs or saliva samples to extract genomic DNA and classify individuals according to four allelic forms (S(A), S(G), L(A), L(G)) of the 5-HTT-linked polymorphic region (5-HTTLPR). We determined whether the 5-HTTLPR genotype predicted change in PTSD severity following treatment (n = 45) and 6 months later (n = 42). RESULTS After controlling for pretreatment PTSD severity and number of treatment sessions, the 5-HTTLPR low-expression genotype group (S or L(G) allele carriers) displayed more severe PTSD 6 months following treatment relative to other patients. CONCLUSIONS This study suggests a genetic contribution to treatment outcome following cognitive behavior therapy and implicates the serotonergic system in response to exposure-based treatments in PTSD.

Duration of posttraumatic stress disorder predicts hippocampal grey matter loss

To examine the impact of environmental stress on grey matter volume in posttraumatic stress disorder (PTSD), we investigated the relationship between duration of PTSD and grey matter volume of hippocampus and anterior cingulate cortex. Twenty-one participants with PTSD and 17 trauma-exposed controls, matched for age and sex and with no history of substance dependence, underwent a T1-weighted structural MRI scan and voxel-based morphometry was employed. After controlling for age, depression and whole-brain volume, analysis of covariance revealed significant reductions in hippocampus and rostral anterior cingulate cortex in PTSD, and there was a significant negative correlation between right hippocampal volume and PTSD duration. This pattern suggests that prolonged PTSD may have cumulative adverse effects on hippocampal volume, highlighting the potential role of genetic–environmental interactions.

Inhibitory neural activity predicts response to cognitive-behavioral therapy for posttraumatic stress disorder.

OBJECTIVE Despite cognitive-behavioral therapy (CBT) being an effective treatment for posttraumatic stress disorder (PTSD), many patients do not respond to CBT. Understanding the neural bases of treatment response may inform treatment refinement, thereby improving treatment response rates. Adequate working memory function is proposed to enable engagement in CBT. METHOD This study employed a Go/No-Go task to examine inhibitory function and its functional brain correlates as predictors of response to CBT in PTSD. Participants were recruited between October 2003 and May 2005. Thirteen treatment-seeking patients who met DSM-IV criteria for PTSD completed the Go/No-Go task while undergoing functional magnetic resonance imaging (fMRI), after which they entered 8 once-weekly sessions of CBT. PTSD severity was measured before treatment and again at 6 months following treatment completion using the Clinician-Administered PTSD Scale (primary outcome measure). RESULTS After controlling for initial PTSD severity and ongoing depressive symptoms, greater activity in left dorsal striatal (Z = 3.19, P = .001) and frontal (Z = 3.03, P = .001) networks during inhibitory control was associated with lower PTSD symptom severity after treatment, suggesting better treatment response. CONCLUSIONS These results suggest that neural circuitry underpinning inhibitory control plays a role in the outcome of CBT for patients with PTSD. TRIAL REGISTRATION anzctr.org Identifier: ACTRN12610000017022.

Reduced Amygdala and Ventral Striatal Activity to Happy Faces in PTSD Is Associated with Emotional Numbing

There has been a growing recognition of the importance of reward processing in PTSD, yet little is known of the underlying neural networks. This study tested the predictions that (1) individuals with PTSD would display reduced responses to happy facial expressions in ventral striatal reward networks, and (2) that this reduction would be associated with emotional numbing symptoms. 23 treatment-seeking patients with Posttraumatic Stress Disorder were recruited from the treatment clinic at the Centre for Traumatic Stress Studies, Westmead Hospital, and 20 trauma-exposed controls were recruited from a community sample. We examined functional magnetic resonance imaging responses during the presentation of happy and neutral facial expressions in a passive viewing task. PTSD participants rated happy facial expression as less intense than trauma-exposed controls. Relative to controls, PTSD participants revealed lower activation to happy (-neutral) faces in ventral striatum and and a trend for reduced activation in left amygdala. A significant negative correlation was found between emotional numbing symptoms in PTSD and right ventral striatal regions after controlling for depression, anxiety and PTSD severity. This study provides initial evidence that individuals with PTSD have lower reactivity to happy facial expressions, and that lower activation in ventral striatal-limbic reward networks may be associated with symptoms of emotional numbing.

Developing an integrated brain, behavior and biological response profile in posttraumatic stress disorder (PTSD).

The present study sought to determine a profile of integrated behavioral, brain and autonomic alterations in PTSD. Previous findings suggest that PTSD is associated with changes across electrophysiological (EEG and ERP), autonomic and cognitive/behavioral measures. In particular, PTSD has been associated with reduced cognitive performance, altered cortical arousal (measured by EEG), diminished late ERP component to oddball task targets (reduced P3 amplitude) and increased autonomic arousal relative to healthy controls. The present study examined measures of cognitive function, auditory oddball ERP components, autonomic function (heart rate and skin conductance) and EEG during resting conditions in 44 individuals with PTSD and 44 non-trauma-exposed controls, and predicted that an integrated profile of changes across a number of these measures would show a high level of sensitivity and specificity in discriminating PTSD from controls. Nine variables showing strongly significant (p < 0.002) between-group differences were entered into a discriminant function analysis. Four of these measures successfully discriminated the PTSD and non-PTSD groups: change in tonic arousal, duration of attention switching, working memory reaction time and errors of commission during visuospatial maze learning. Tonic arousal change contributed the most variance in predicting group membership. These results extend previous findings and provide an integrated biomarker profile that characterizes both PTSD and non-PTSD groups with a high degree of sensitivity and specificity. This outcome provides a platform for future studies to test how this profile of disturbances in autonomic and information processing may be unique to PTSD or may occur generically across clinical and/or other anxiety disorders.

Heterogeneity of non-conscious fear perception in posttraumatic stress disorder as a function of physiological arousal: An fMRI study

While posttraumatic stress disorder (PTSD) is often characterised by an excessive fear response and hyperarousal, research has generally neglected other clinical characteristics including hypoarousal. Findings indicate that concurrent autonomic activity is associated with increased non-conscious processing of fear, highlighting that autonomic responsivity may be an important determinant in the degree of activation within the brainstem-amygdala-MPFC (medial prefrontal cortex) network.

Alterations in theta activity associated with novelty and routinization processing in ADHD

OBJECTIVE Novelty and routinization-related information processing disturbances were examined in adolescent males with ADHD using an oddball paradigm and electrophysiological measurement of theta (4-7Hz) activity. METHODS Fifty-four unmedicated adolescent males (12-18years) with Attention Deficit Hyperactivity Disorder (ADHD) and matched controls performed an auditory oddball task. Theta activity was sub-averaged, and Fourier Integrals with simultaneous measurement of electrodermal activity (EDA) was used to index response to stimulus novelty and routinization. RESULTS ADHD participants showed an overall increase in theta activity to both novel and routine stimuli relative to controls. While controls showed increased theta activity in response to novel compared to routine targets across the brain, ADHD participants did not show this novelty-related increase in theta activity in the right anterior/frontal brain. CONCLUSIONS The findings of this study are consistent with disturbances in theta activity and the brain substrates of novelty relative to routinization-related processing in ADHD. SIGNIFICANCE These findings show that there are distinct alterations in theta activity related to stimulus novelty and routinization during an auditory oddball task in ADHD, and they highlight the value of using an event-related approach to elucidate the neural substrates of stimulus processing in ADHD.