1Department of Psychology, Creighton University, Omaha, NE 2Center for ... Avoidance symptoms (avoiding trauma related thoughts, people, places, etc.).
Magnetoencephalography Reveals Neurocognitive Deficits during an Emotional Stroop Task in Veterans with PTSD 1,2Timothy
J. McDermott, 1Amy Badura Brack, 1Maya Khanna, 1Alex Shepherd, 2,3Elizabeth Heinrichs-Graham, & 2,4,5Tony W. Wilson 1Department
of Psychology, Creighton University, Omaha, NE 2Center for Magnetoencephalography, University of Nebraska Medical Center (UNMC), Omaha, NE 3Department of Psychology, University of Nebraska – Omaha, 4Department of Pharmacology & Experimental Neuroscience, UNMC, Omaha, NE 5Department of Neurological Sciences, UNMC, Omaha, NE
INTRODUCTION Symptoms of posttraumatic stress disorder (PTSD) include (APA 2000, APA 2013): • Experiencing a traumatic event (e.g. combat, assault, motor vehicle accident) • Intrusion symptoms (intrusive thoughts, nightmares, flashbacks) • Avoidance symptoms (avoiding trauma related thoughts, people, places, etc.) • Negative mood and cognition (loss of interest, emotional numbing, withdrawal) • Hyperarousal (trouble sleeping, hypervigilance, irritability, and aggression) Posttraumatic stress disorder (PTSD) has been associated with information processing biases and deficits (Cisler et al., 2011). One of the well-studied cognitive difficulties in PTSD is an attentional bias to threatening stimuli. This attentional bias can be linked to anxiety-related symptoms in PTSD (Sipos et al., 2013). Recent research has also revealed that the tendency of attention bias to fluctuate between threat vigilance and threat avoidance (attention bias variability, ABV), is reliably correlated with PTSD symptoms (Iacovello et al., 2014; Naim et al., 2015). The emotional Stroop task is a cognitive task that has been used in previous studies to examine the impacts of PTSD on threat-bias and attentional control mechanisms as well as the neurobiological correlates of these deficits (Friese et al., 2013). Stroop tasks (Lezak, 1995; Stroop, 1935, 1992) compare reaction times for naming the color ink that various words are presented in. This is a task of inhibiting a reflexive response (reading) involving executive control. The emotional Stroop task used for this study includes neutral, negative, and combat specific words to measure participants’ attentional bias towards threat.
RESULTS
METHODS MEG Acquisition & Data Pre-Processing: Neuromagnetic responses were sampled continuously at 1kHz using an Elekta Neuromag system with 306 magnetic sensors. Throughout the recording, participants were seated in a chair within a magneticallyshielded room. Data were corrected for head motion, subjected to noise reduction using signal space separation with a temporal extension (tSSS; Taulu & Simola, 2006), and coregistered to a neuroanatomical volume based on T1-weighted magnetic resonance images (MRI). Time Frequency Analyses & Statistics: Artifact-free trials were transformed into the time frequency domain using complex demodulation. The specific time-frequency windows used for beamforming were determined by statistical analysis of the spectrograms corresponding to the MEG sensors. Each data point in the spectrogram was probed for significant oscillatory deviations (relative to the baseline) using a mass univariate approach based on the general linear model. Time-frequency bins that survived the (p < 0.05) threshold were clustered with significant temporally or spectrally neighboring bins, and a cluster value was derived by summing all tvalues in the cluster. Nonparametric permutation testing was then used to derive a distribution of cluster-values, and the significance level of the observed clusters were tested using this distribution. Beamforming & Statistical Analyses: Cortical networks were imaged through an extension of the linearlyconstrained minimum variance vector beamformer. Normalized source power was computed for the time-frequency bin of interest per participant at 4.0 x 4.0 x 4.0 mm resolution. The effect of group was examined using a random effects analysis for the time-frequency bin of interest, while one-sample t-tests were conducted to probe activation patterns in each group. Permutation testing was used to reduce the risk of false positives.
METHODS Participants: 27 male combat veterans (OEF, OIF) diagnosed with PTSD using the Clinician Administered PTSD Scale (CAPS; Blake, et al., 1995) and 17 psychologically healthy, demographically-matched combat veterans (OEF, OIF) volunteered for this research. All participants provided informed consent to participate in this study, which was reviewed and approved by the Creighton University IRB. Task: Our modified EST used three different word lists: neutral (tune), negative (witch), and combat-related (bomb) word lists to measure participants’ attentional bias towards threat. These lists were matched across a series of lexical variables.
RESULTS Task Performance: 44 participants were able to successfully complete the emotional Stroop task. Our results showed that, male veterans with PTSD exhibited a strong EST effect (longer colour-naming latencies) as they were slower for combat-related words compared to neutral words (p =.014). Veterans without PTSD did not show this same EST effect. MEG Imaging of Theta Activity: Task Effects for Combat Words Veterans with PTSD
Veterans without PTSD
Magnetoencephalography (MEG): Magnetoencephalography (MEG) is a noninvasive neurophysiological recording method that quantifies neural activity by measuring the magnetic fields generated by the brain’s neuronal activity. The major advantage of MEG over other leading neuroimaging technologies (e.g., functional magnetic resonance imaging) is its ability to measure shifts in brain activity to the millisecond while maintaining spatial precision.
MEG recordings are done in a special shielded room, which looks like a bank vault. This ensures that only the magnetic fields generated by the brain are detected by the 306 sensors (above) located inside the helmet of the MEG machine (left).
MEG Imaging of Theta Activity: Group Differences
Group Differences
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Figure 2. MEG Group Differences during EST Performance: The differences in activation between the PTSD veterans and the non-PTSD veterans were evaluated using a two-sample t-test and the image above displays the group comparison SPM for the theta frequency band (4-8 Hz) during the 400-600ms time window (p < 0.00001, corrected). These neurophysiological differences were localized to the ventral medial prefrontal cortex (vmPFC) of the right hemisphere. Figure 3. Peak Voxel Correlations: Clinical measures were correlated with the t-values extracted from the peak voxel of the difference between groups. Peak voxel values for theta activity in the ventromedial prefrontal cortex (vmPFC) were inversely correlated (r = -.55, p
