Abstract
BackgroundPersistent postconcussion syndrome (PCS) occurs in around 5–10% of individuals after mild traumatic brain injury (mTBI), but research into the underlying biology of these ongoing symptoms is limited and inconsistent. One reason for this could be the heterogeneity inherent to mTBI, with individualized injury mechanisms and psychological factors. A multimodal imaging study may be able to characterize the injury better.AimTo look at the relationship between functional (fMRI), structural (diffusion tensor imaging), and metabolic (magnetic resonance spectroscopy) data in the same participants in the long term (>1 year) after injury. It was hypothesized that only those mTBI participants with persistent PCS would show functional changes, and that these changes would be related to reduced structural integrity and altered metabolite concentrations.MethodsFunctional changes associated with persistent PCS after mTBI (>1 year postinjury) were investigated in participants with and without PCS (both n = 8) and non-head injured participants (n = 9) during performance of working memory and attention/processing speed tasks. Correlation analyses were performed to look at the relationship between the functional data and structural and metabolic alterations in the same participants.ResultsThere were no behavioral differences between the groups, but participants with greater PCS symptoms exhibited greater activation in attention-related areas (anterior cingulate), along with reduced activation in temporal, default mode network, and working memory areas (left prefrontal) as cognitive load was increased from the easiest to the most difficult task. Functional changes in these areas correlated with reduced structural integrity in corpus callosum and anterior white matter, and reduced creatine concentration in right dorsolateral prefrontal cortex.ConclusionThese data suggest that the top-down attentional regulation and deactivation of task-irrelevant areas may be compensating for the reduction in working memory capacity and variation in white matter transmission caused by the structural and metabolic changes after injury. This may in turn be contributing to secondary PCS symptoms such as fatigue and headache. Further research is required using multimodal data to investigate the mechanisms of injury after mTBI, but also to aid individualized diagnosis and prognosis.
Highlights
Traumatic brain injury (TBI) is a common cause of hospital admission in both the USA [1.6 million in 2003 (Rutland-Brown et al 2006)] and the UK [156,000 in 2007 (Goodacre 2008)], with around 70–90% of those admissions having mild traumatic brain injury(Cassidy et al 2004; Goodacre 2008)
This study aims to investigate functional differences 1 year post mild traumatic brain injury (mTBI) in the same sample as the previous neuroimaging studies (Dean et al 2013), and their relationship with postconcussion syndrome (PCS) symptoms, cognitive performance, and the previously observed metabolic and structural changes
In addition to differences in prefrontal Blood Oxygen Level Dependent (BOLD) response, this study found that participants with higher PCS symptom scores exhibit a greater reduction in BOLD response in default mode network (DMN)-related areas (PCC, precuneus) and the right thalamus when performing the hardest compared to the easiest Paced Visual Serial Addition Task (PVSAT) condition
Summary
Traumatic brain injury (TBI) is a common cause of hospital admission in both the USA [1.6 million in 2003 (Rutland-Brown et al 2006)] and the UK [156,000 in 2007 (Goodacre 2008)], with around 70–90% of those admissions having mild traumatic brain injury (mTBI)(Cassidy et al 2004; Goodacre 2008). Results: There were no behavioral differences between the groups, but participants with greater PCS symptoms exhibited greater activation in attention-related areas (anterior cingulate), along with reduced activation in temporal, default mode network, and working memory areas (left prefrontal) as cognitive load was increased from the easiest to the most difficult task Functional changes in these areas correlated with reduced structural integrity in corpus callosum and anterior white matter, and reduced creatine concentration in right dorsolateral prefrontal cortex. Further research is required using multimodal data to investigate the mechanisms of injury after mTBI, and to aid individualized diagnosis and prognosis
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