Diffuse disconnectivity in traumatic brain injury: a resting state fMRI and DTI study

Diffuse axonal injury is a common pathological consequence of Traumatic Brain Injury (TBI). Diffusion Tensor Imaging is an ideal technique to study white matter integrity using the Fractional Anisotropy (FA) index which is a measure of axonal integrity and coherence. There have been several reports showing reduced FA in individuals with TBI, which suggest demyelination or reduced fiber density in white matter tracts secondary to injury. Individuals with TBI are usually diagnosed with cognitive deficits such as reduced attention span, memory and executive function. In this study we sought to investigate correlations between brain functional networks, white matter integrity, and TBI severity in individuals with TBI ranging from mild to severe. A resting state functional magnetic resonance imaging protocol was used to study the default mode network in subjects at rest. FA values were decreased throughout all white matter tracts in the mild to severe TBI subjects. FA values were also negatively correlated with TBI injury severity ratings. The default mode network showed several brain regions in which connectivity measures were higher among individuals with TBI relative to control subjects. These findings suggest that, subsequent to TBI, the brain may undergo adaptation responses at the cellular level to compensate for functional impairment due to axonal injury.