Dynamical measures in PTSD related to the P3 Working Memory ERP

Proposal details

Title: Dynamical measures in PTSD related to the P3 Working Memory ERP
Research Area(s): PTSD and other Anxiety Disorders
Background: The P3WM has been shown to be abnormal in PTSD previous studies. In this study we are able to relate this ERP component to number of dynamical measures to this explore further this characteristics of this abnormality. This study utilizes new measures event-related phase dynamics in EEG (Alexander et al., 2006). The measures enable dynamical travelling wave activity at the global cortical scale to be measured at the surface of the scalp. This wave activity is the cortical equivalent to waves on a pond spreading from a dropped stone. The direction of wave propagation can also be measured, and this study focuses on the measure of propagation along the peripheral to central axis of the scalp, i.e. components of wave activity travelling from peripheral sites (i.e. Fp1, Fp2, T3, T4, T5, T6, O1, Oz, O2) to central sites (e.g. Cz). The study also uses a new measure of Instantaneous Phase Synchrony. Instantaneous Phase Synchrony differs from previous phase synchrony measures (Haig et al., 2000) in that the latter measure estimates phase over a window lasting ~10 cycles, using fast Fourier transform. Instantaneous Phase Synchrony measures phase-locking over less than one cycle.
Aims: To relate the P3WM to dynamical measures of EEG activity. To further elucidate the abnormal P3WM in PTSD via dynamical measures of EEG activity. To relate the dynamical measures to clinical scores in the PTSD group. To show that dynamical methods, which use single trial analysis as their basis, are more sensitive to group differences and clinical relationships.
Method: This study compares 34 PTSD subjects with 128 age and gender matched controls. This study uses the clinical scales PTSD check-list total (PCLtot) and Clinician Administered PTSD Scale total (CAPStot) and relates them to EEG measures. EEG was analyzed from a Visual Working Memory task, backgrounds condition, at 26 electrodes. The spatial patterns of wave activity across the scalp were assessed along the scalp directions of anterior-posterior, peripheral-central and right-left. These three measures quantify the amount that each direction-specific component contributes to the wave activity, and this study focuses on the peripheral-central component. In addition, the global Instantaneous Phase Synchrony was measured i.e. the extent of zero-lag phase-locking across all 26 electrodes at a given frequency, or global standing waves. For the measure of the peripheral-central component of wave activity, the phases were estimated using a 2-cycle Morlet wavelet (Alexander et al., 2006). For the measure of Instantaneous Phase Synchrony, the phases were estimated using a 1-cycle Morlet wavelet. Multiple t-tests were used to distinguish the PTSD group from matched controls on the two EEG measures (peripheral-central component of wave activity, Instantaneous Phase Synchrony) for the frequencies 0.2 to 32Hz, from -200ms pre-stimulus to 800ms post-stimulus at 10ms intervals. The same EEG measures were correlated with symptom scales within the PTSD group to see which elements of dynamical activity predict symptomology. To avoid type I errors, in each of these analyses, results were only counted as significant if at least 20 contiguous time/frequency points were significant at p