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Published May 2019 | Supplemental Material
Journal Article Open

MEG Working Memory N-Back Task Reveals Functional Deficits in Combat-Related Mild Traumatic Brain Injury

Abstract

Combat-related mild traumatic brain injury (mTBI) is a leading cause of sustained cognitive impairment in military service members and Veterans. However, the mechanism of persistent cognitive deficits including working memory (WM) dysfunction is not fully understood in mTBI. Few studies of WM deficits in mTBI have taken advantage of the temporal and frequency resolution afforded by electromagnetic measurements. Using magnetoencephalography (MEG) and an N-back WM task, we investigated functional abnormalities in combat-related mTBI. Study participants included 25 symptomatic active-duty service members or Veterans with combat-related mTBI and 20 healthy controls with similar combat experiences. MEG source–magnitude images were obtained for alpha (8–12 Hz), beta (15–30 Hz), gamma (30–90 Hz), and low-frequency (1–7 Hz) bands. Compared with healthy combat controls, mTBI participants showed increased MEG signals across frequency bands in frontal pole (FP), ventromedial prefrontal cortex, orbitofrontal cortex (OFC), and anterior dorsolateral prefrontal cortex (dlPFC), but decreased MEG signals in anterior cingulate cortex. Hyperactivations in FP, OFC, and anterior dlPFC were associated with slower reaction times. MEG activations in lateral FP also negatively correlated with performance on tests of letter sequencing, verbal fluency, and digit symbol coding. The profound hyperactivations from FP suggest that FP is particularly vulnerable to combat-related mTBI.

Additional Information

© 2018 The Author(s). Published by Oxford University Press. Received: 09 November 2017; Revision Received: 11 March 2018; Accepted: 13 March 2018; Published: 13 April 2018. Funding: Supported in part by Merit Review Grants from the U.S. Department of Veterans Affairs to M.X. Huang (I01-CX000499, I01-RX001988, MHBA-010-14F, NURC-022-10F, NEUC-044-06S), R.R. Lee, D.L. Harrington (I01-CX000146), and The U.S. Naval Medical Research Center's Advanced Medical Development program (Naval Medical Logistics Command Contract #N62645-11-C-4037, for MRS-II (D.G. Baker, M.A. Geyer, M.X. Huang, V.B. Risbrough). We acknowledge the MRS-II administrative core, Anjana Patel, Andrew De La Rosa, and members of the MRS-II Team, including logistic coordinators, clinician–interviewers, and data collection staff. We thank staff at the VA San Diego Healthcare System and the Veterans Medical Research Foundation (VRMF). We also thank the participating Marines and Veteran volunteers for their military service and participation in this study. Furthermore, we thank 3 anonymous reviewers for their constructive critiques and suggestions which substantially strengthened the paper. Conflict of interest: none declared.

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Created:
August 19, 2023
Modified:
October 18, 2023