Objectives: Recent advances in neuroimaging methodologies sensitive to axonal injury have made it possible to assess in vivo the extent of traumatic brain injury (TBI) -related disruption in neural structures and their connections. The objective of this paper is to review studies examining connectivity in TBI with an emphasis on structural and functional MRI methods that have proven to be valuable in uncovering neural abnormalities associated with this condition. Methods: We review studies that have examined white matter integrity in TBI of varying etiology and levels of severity, and consider how findings at different times post-injury may inform underlying mechanisms of post-injury progression and recovery. Moreover, in light of recent advances in neuroimaging methods to study the functional connectivity among brain regions that form integrated networks, we review TBI studies that use resting-state functional connectivity MRI methodology to examine neural networks disrupted by putative axonal injury. Results: The findings suggest that TBI is associated with altered structural and functional connectivity, characterized by decreased integrity of white matter pathways and imbalance and inefficiency of functional networks. These structural and functional alterations are often associated with neurocognitive dysfunction and poor functional outcomes. Conclusions: TBI has a negative impact on distributed brain networks that lead to behavioral disturbance. (JINS, 2016, 22, 120–137)

Traumatic brain injury (TBI) is associated with long-term changes in daily life functioning, yet the neuroanatomical correlates of these changes are poorly understood. This study related outcome assessed across several domains to brain structure derived from quantitative magnetic resonance imaging (MRI). Sixty individuals spanning a wide range of TBI severity participated 1-year post-injury as part of the Toronto TBI study. Volumetric data over 38 brain regions were derived from high resolution T1-weighted MRI scans. Functioning was assessed with a battery of self- and significant-other rated measures. Multivariate analysis (partial least squares) was used to identify shared variance between the neuroimaging and outcome measures. TBI was associated with item endorsement on outcome questionnaires without strong evidence for severity or focal lesion effects. Prefrontal midline, cingulate, medial temporal, right inferior parietal and basal ganglia/thalamic volumes were associated with measures of initiative, energization, and physical complaints. In the chronic stage of TBI, self-initiation, energization, and physical complaints related to a specific pattern of volume loss in midline and lateral regions known to be involved in motivation, apathy, and attention. These results suggest that crucial functional changes in chronic TBI may be associated with volume loss in established midline-frontal and attentional circuits. (JINS, 2015, 21, 650–655)

We examined the long-term retention of a learned automatic cognitive process in 17 severe TBI participants and 10 controls. Participants had initially received extensive consistent-mapping (CM) training (i.e., 3600 trials) in a semantic category visual search task (Schmitter-Edgecombe & Beglinger, 2001). Following CM training, TBI and control groups demonstrated dramatic performance improvements and the development of an automatic attention response (AAR), indicating task-specific and stimulus-specific skill learning. After a 5- or 10-month retention interval, participants in this study performed a New CM task and the originally trained CM task to assess for retention of task-specific and stimulus-specific visual search skills, respectively. No significant group differences were found in the level of retention for either skill type, indicating that individuals with severe TBI were able to retain the learned skills over a long-term retention interval at a level comparable to controls. Exploratory analyses revealed that TBI participants who returned at the 5-month retention interval showed nearly complete skill retention, and greater skill retention than TBI participants who returned at the 10-month interval, suggesting that “booster” or retraining sessions may be needed when a skill is not continuously in use. (JINS, 2006, 12, 802–811.)