Thalamic Structural Connectivity and Cognitive Outcome in the Subacute Period Following Mild Traumatic Brain Injury

Emerging evidence suggests the thalamus may be a relevant structure in mild traumatic brain injury (mTBI). However, the structural connectivity profile of the thalamus has not been investigated in mTBI, nor have thalamic contributions to cognitive function been characterized in this population. This study investigated the relative strength of connectivity from thalamic subregions following mTBI and subsequently studied the associations between these metrics and cognitive performance. The final analyzed dataset included 39 mTBI patients and 28 trauma control (TC) patients aged 18-60 years, who were recruited following hospital admission for physical injury. Participants completed a magnetic resonance imaging (MRI) protocol including both structural MRI and multishell diffusion-weighted MRI sequences at 6-12 weeks (mean = 57 days, standard deviation = 11) post-injury. Thalamic segmentations were combined with cortical and subcortical parcellations to define nodes of each participant's structural connectivity network. Connectivity matrices were generated by mapping streamline reconstruction onto the 179 parcels. Nodal edge strength, representing the weighted connections of thalamic subregion edges, was calculated. Participants also completed a range of cognitive tests examining processing speed, attention, memory, and executive functions. The two groups were comparable with respect to thalamic subregion edge strength and performance on cognitive tests. These primary findings suggest that nodal structural connectivity of the thalamus is normal at this time point following injury. Moderation analysis revealed several interactions between group and edge strength predicting cognitive performance, namely, increased edge strength generally predicted better cognitive performance in the TC group, but worse performance in the mTBI group. These preliminary findings require further validation, although they raise the question as to whether sustaining an mTBI results in a change in the relationship between thalamic structure and cognitive function 6-12 weeks after injury.