Deficits in Visual System Functional Connectivity after Blast‐Related Mild TBI are Associated with Injury Severity and Executive Dysfunction

Abstract

IntroductionApproximately, 275,000 American service members deployed to Iraq or Afghanistan have sustained a mild traumatic brain injury (mTBI), with 75% of these incidents involving an explosive blast. Visual processing problems and cognitive dysfunction are common complaints following blast‐related mTBI.MethodsIn 127 veterans, we examined resting fMRI functional connectivity (FC) of four key nodes within the visual system: lateral geniculate nucleus (LGN), primary visual cortex (V1), lateral occipital gyrus (LO), and fusiform gyrus (FG). Regression analyses were performed (i) to obtain correlations between time‐series from each seed and all voxels in the brain, and (ii) to identify brain regions in which FC variability was related to blast mTBI severity. Blast‐related mTBI severity was quantified as the sum of the severity scores assigned to each of the three most significant blast‐related injuries self‐reported by subjects. Correlations between FC and performance on executive functioning tasks were performed across participants with available behavioral data (n = 94).ResultsGreater blast mTBI severity scores were associated with lower FC between: (A) LGN seed and (i) medial frontal gyrus, (ii) lingual gyrus, and (iii) right ventral anterior nucleus of thalamus; (B) V1 seed and precuneus; (C) LO seed and middle and superior frontal gyri; (D) FG seed and (i) superior and medial frontal gyrus, and (ii) left middle frontal gyrus. Finally, lower FC between visual network regions and frontal cortical regions predicted worse performance on the WAIS digit‐symbol coding task.ConclusionThese are the first published results that directly illustrate the relationship between blast‐related mTBI severity, visual pathway neural networks, and executive dysfunction – results that highlight the detrimental relationship between blast‐related brain injury and the integration of visual sensory input and executive processes.

Resting-State Magnetoencephalography Reveals Different Patterns of Aberrant Functional Connectivity in Combat-Related Mild Traumatic Brain Injury

“…Unlike the more traditional method of spectral coherence, PLS separates the phase and amplitude components and can be directly interpreted in the framework of neural integration. 80 In the present study, the frequency increments used in the Morlet wavelet transformation were at 0.5 Hz for the low-frequency band (1-7 Hz) and alpha band (8-12 Hz), at 1 Hz for the beta band (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), and at 2 Hz for the gamma band . Similar to the Xcorr approach, ROIglobal FC measures were obtained using the PLS approach as the ROI-global connectivity vector with 94 elements.…”

“…[33][34][35][36][37][38][39][40][41] Twenty-one of these rs-fMRI studies were concerned with blunt mTBI whereas only four were related to blast mTBI. In the four blast mTBI studies, Gilmore and colleagues found reduced FC between visual network regions and other brain areas, 23 Robinson and colleagues found decreased FC of bilateral primary somatosensory and motor cortices, 28 Han and colleagues found increased within-module FC, but decreased inter-module FC, 33 and Vakhtin and colleagues found decreased FC among various brain networks (default mode network [DMN]-basal ganglia, attention-sensorimotor, frontal-DMN, attentionfrontal, and sensorimotor-sensorimotor). 32 The reasons for these discrepant findings is unclear, but may partially relate to the use of different analytic approaches.…”

“…Although disturbances in FC have been reported in many studies of mTBI, there are large discrepancies in the findings. For example, out of 25 resting-state functional magnetic resonance imaging (rs-fMRI) studies of mTBI, 6 showed only increased FC, [17][18][19][20][21][22] 9 showed only decreased FC, [23][24][25][26][27][28][29][30][31][32] and 10 showed both increased FC in some brain networks/regions and decreased FC in other networks/regions. [33][34][35][36][37][38][39][40][41] Twenty-one of these rs-fMRI studies were concerned with blunt mTBI whereas only four were related to blast mTBI.…”

Constructing fine-granularity functional brain network atlases via deep convolutional autoencoder

“…Notably, ICN 1 is brain stem network, ICN 6 and 7 are visual networks, and ICN 17 is auditory network, which are all reported in the literature with decreased activation among mTBI patients. As in (Gilmore et al, 2016; Iraji et al, 2015; Stevens et al, 2012a), the visual processing circuit, including bilateral visual cortex (ICN 7), showed decreased functional connectivity; in (Iraji et al, 2015; Stevens et al, 2012b), diminished functional connectivity was also found for the motor systems (ICN 13); in (Schairer et al, 2012; Vander Werff, 2012), the mechanisms of injury to the auditory system in the mTBI was introduced and dysfunctions on auditory network were reported (ICN 17). In particular, the brainstem (Kushner et al, 1998), which has cranial nerves for eye movements and the auditory pathway, also showed decreased functional connectivity in mTBI patient group than the control group, relative to the visual and auditory networks.…”

Clinical validation of an optimized multimodal neurocognitive assessment of chronic mild TBI

“…Eye movement abnormalities in TBI could be related to the broad network of regions that must communicate effectively to acquire and integrate information from the visual environment 22 . Impaired eye movements have been linked to axonal injury in postmortem tissue and on diffusion tensor imaging; 23‐25 abnormal functional connectivity in chronic mTBI extends to the visual system and its interactions with higher‐order cognitive processing 26 . Importantly, the types of eye movements that are most strongly impacted by mTBI are those that most heavily rely upon effective cognitive processing, as opposed to measures of basic neuromotor function 14,18,27‐29 .…”