Theta, mental flexibility, and post-traumatic stress disorder: connecting in the parietal cortex.

Dunkley, Benjamin T; Sedge, Paul A; Doesburg, Sam M; Grodecki, Richard J; Jetly, Rakesh; Shek, Pang N; Taylor, Margot J; Pang, Elizabeth W · 2015 · DOAJ

DOI: 10.1371/journal.pone.0123541

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Summary

This study investigates the neural mechanisms underlying cognitive deficits in post-traumatic stress disorder (PTSD), specifically focusing on mental flexibility and executive function. While PTSD is well-characterized by symptoms such as re-experiencing and hyperarousal, the prevalence and neurobiological basis of associated cognitive sequelae remain debated. Conflicting reports exist regarding deficits in mental flexibility, particularly in fast-paced, attentionally-demanding tasks. To address this, the authors examined task-dependent functional connectivity in combat-related PTSD patients compared to military controls, hypothesizing that atypical neural synchronization contributes to observed behavioral impairments. The researchers utilized magnetoencephalography (MEG) to assess 18 male veterans with combat-related PTSD and 19 matched male military controls. Participants performed a set-shifting task involving intra-dimensional (simpler) and extra-dimensional (more attentionally demanding) shifts. The study employed source-resolved inter-regional phase synchronization and graph theoretical analysis to evaluate frequency-specific interactions, particularly in the theta (4–7 Hz), alpha, and beta bands. Behavioral performance was measured via reaction time and accuracy, while clinical assessments included measures of attention, anxiety, and depression. Behavioral results indicated that while reaction times did not differ significantly between groups, the PTSD group exhibited significantly lower accuracy during the extra-dimensional shifts compared to controls. Neuroimaging analysis revealed large-scale increases in theta connectivity in the PTSD group. During the intra-dimensional task, PTSD patients showed elevated theta coherence in the 100–300 ms window post-stimulus. In the more demanding extra-dimensional task, significant group differences emerged only in the late-stage (300–400 ms) window, characterized by hyperconnectivity centered on the right superior parietal lobule (SPL). This region displayed a delayed return to baseline connectivity levels in PTSD patients. Furthermore, theta connectivity strength in the right parietal cortex correlated positively with clinical scores for attention deficits, anxiety, and depression. Notably, while connectivity in this region correlated with reaction time in controls, this relationship was absent in the PTSD group, suggesting a decoupling of neural efficiency and performance. The findings suggest that atypical theta-band synchronization, particularly involving the right parietal cortex, underlies deficits in mental flexibility in PTSD. The observed hyperconnectivity may reflect inefficient neural coordination or compensatory mechanisms that fail to support effective cognitive control in timed, complex tasks. These results imply that network hyperconnectivity is not merely a byproduct but may play a general role in the cognitive and emotional sequelae of PTSD, providing a neurophysiological marker for the disorder’s impact on executive function.

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