White matter integrity following traumatic brain injury: the association with severity of injury and cognitive functioning.

Traumatic brain injury (TBI) frequently results in impairments of memory, speed of information processing, and executive functions that may persist over many years. Diffuse axonal injury is one of the key pathologies following TBI, causing cognitive impairments due to the disruption of cortical white matter pathways. The current study examined the association between injury severity, cognition, and fractional anisotropy (FA) following TBI. Two diffusion tensor imaging techniques-region-of-interest tractography and tract-based spatial statistics-were used to assess the FA of white matter tracts. This study examined the comparability of these two approaches as they relate to injury severity and cognitive performance. Sixty-eight participants with mild-to-severe TBI, and 25 healthy controls, underwent diffusion tensor imaging analysis. A subsample of 36 individuals with TBI also completed cognitive assessment. Results showed reduction in FA values for those with moderate and severe TBI, compared to controls and individuals with mild TBI. Although FA tended to be lower for individuals with mild TBI no significant differences were found compared to controls. Information processing speed and executive abilities were most strongly associated with the FA of white matter tracts. The results highlight similarities and differences between region-of-interest tractography and tract-based spatial statistics approaches, and suggest that they may be used together to explore pathology following TBI.