Abstract
Mild traumatic brain injury (mTBI) has been firmly associated with disrupted white matter integrity due to induced white matter damage and degeneration. However, comparatively less is known about the changes of the intrinsic functional connectivity mediated via neural synchronization in the brain after mTBI. Moreover, despite the presumed link between structural and functional connectivity, no existing studies in mTBI have demonstrated clear association between the structural abnormality of white matter axons and the disruption of neural synchronization. To investigate these questions, we recorded resting state EEG and diffusion tensor imaging (DTI) from a cohort of military service members. A newly developed synchronization measure, the weighted phase lag index was applied on the EEG data for estimating neural synchronization. Fractional anisotropy was computed from the DTI data for estimating white matter integrity. Fifteen service members with a history of mTBI within the past 3 years were compared to 22 demographically similar controls who reported no history of head injury. We observed that synchronization at low-gamma frequency band (25–40 Hz) across scalp regions was significantly decreased in mTBI cases compared with controls. The synchronization in theta (4–7 Hz), alpha (8–13 Hz), and beta (15–23 Hz) frequency bands were not significantly different between the two groups. In addition, we found that across mTBI cases, the disrupted synchronization at low-gamma frequency was significantly correlated with the white matter integrity of the inferior cerebellar peduncle, which was also significantly reduced in the mTBI group. These findings demonstrate an initial correlation between the impairment of white matter integrity and alterations in EEG synchronization in the brain after mTBI. The results also suggest that disruption of intrinsic neural synchronization at low-gamma frequency may be a characteristic functional pathology following mTBI and may prove useful for developing better methods of diagnosis and treatment.
Highlights
Traumatic brain injury (TBI) is a major health challenge in both civilian and military populations [1, 2]
Fifteen individuals with Mild traumatic brain injury (mTBI) occurring in the past 3 years and 22 individuals with no history of head injury were included in this study for comparisons. Both mTBI and controls were from the same cohort of military service members within 2 months of their return from a deployment in either Iraq or Afghanistan
In order to identify oscillatory frequencies in neural synchronization showing abnormality following mTBI, we first performed the tests on the theta (4–7 Hz), alpha (8–13 Hz), beta (15–23 Hz), and low-gamma (25–40 Hz) frequency bands for weighted phase lag index (WPLI) spectra averaged across all electrode pairs
Summary
Traumatic brain injury (TBI) is a major health challenge in both civilian and military populations [1, 2]. Mild TBI (mTBI) is estimated to account for over 85% of all TBI cases [3]. MTBI has been recognized as a signature wound of the wars in Iraq and Afghanistan [4]. According to surveys [5,6,7], approximately 15–23% of returning soldiers suffer from mTBI. Following an mTBI individuals often experience difficulties in cognitive functions such as memory, executive function and processing speed [8, 9], resulting in a significant negative impact on quality of life. The exact pathophysiology underlying the cognitive sequelae of mTBI remains unclear
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