Are functional deficits in concussed individuals consistent with white matter structural alterations: combined FMRI & DTI study

Abstract

There is still controversy in the literature whether a single episode of mild traumatic brain injury (MTBI) results in short-term functional and/or structural deficits as well as any induced long-term residual effects. With the inability of traditional structural brain imaging techniques to accurately diagnosis MTBI, there is hope that more advanced applications like functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) will be more specific in diagnosing MTBI. In this study, 15 subjects who have recently suffered from sport-related MTBI and 15 age-matched normal controls underwent both fMRI and DTI to investigate the possibility of traumatic axonal injury associated with functional deficits in recently concussed but asymptomatic individuals. There are several findings of interest. First, MTBI subjects had a more disperse brain activation pattern with additional increases in activity outside of the shared regions of interest (ROIs) as revealed by FMRI blood oxygen level-dependent (BOLD) signals. The MTBI group had additional activation in the left dorsal-lateral prefrontal cortex during encoding phase of spatial navigation working memory task that was not observed in normal controls. Second, neither whole-brain analysis nor ROI analysis showed significant alteration of white matter (WM) integrity in MTBI subjects as evidenced by fractional anisotropy FA (DTI) data. It should be noted, however, there was a larger variability of fractional anisotropy (FA) in the genu, and body of the corpus callosum in MTB subjects. Moreover, we observed decreased diffusivity as evidenced by apparent diffusion coefficient (ADC) at both left and right dorsolateral prefrontal cortex (DL-PFC) in MTBI subjects (P < 0.001). There was also a positive correlation (P < 0.05) between ADC and % change of fMRI BOLD signals at DL-PFC in MTBI subjects, but not in normal controls. Despite these differences we conclude that overall, no consistent findings across advanced brain imaging techniques (fMRI and DTI) were observed. Whether the lack of consistency across research techniques (fMRI & DTI) is due to time frame of scanning, unique nature of MTBI and/or technological issues involved in FA and Apparent Diffusion Coefficient (ADC) quantification is yet to be determined.

Fig. 1

a View of the virtual corridor used for navigation tasks under study and b floor plan, and a sample of the route for one of the runs. The subjects were instructed to reproduce (e.g., retrieve the previously shown route (e.g., encoding) via navigation through virtual corridor by MRI-compatible joystick and to find the target location

Fig. 2

a Sagittal view of corpus callosum subdivided into genu, body, and splenium ROIs. b Sagittal view of the right hippocampus ROI used in the tractography analysis

Fig. 3

a Series of axial images showing the activation pattern of encoding (E) versus baseline (BL) contrast, normal controls. b Axial activation pattern during (E-BL) contrast, MTBI subjects

Fig. 4

Cascade display of TBSS results showing no statistical significant difference between normal control and MTBI groups. Common white matter fiber tracts and FA values are designated in green. No statistical significance was found which would be designated by the color red

Fig. 5

Fiber tracts going through the corpus callosum ROIs of a representative normal control subject (a) and a representative MTBI patient (b). Fiber tracts connected to the right hippocampus ROI of a representative normal control subject (c) and a representative MTBI patient (d)

Fig. 6

The FA values scatter plots of the control and patient group. It should be noted that the FA variations of patients are larger than those of controls except the splenium ROI

Fig. 7

Fiber tracts going through additional ROI including left and right DL-PFC, Precuneus (both sagittal and axial views) and Visual Cortex (V1) for both normal controls and MTBI subjects

Fig. 8

Scatterplots of ADC from left and right DL-PFC seed voxels relative to % change FMRI signal at these ROI for normal controls and MTBI subjects. Best-fit lines are indicated in solid black (NC) and dashed red (MTBI)