Editor’s Choice: Altered Relationship between Working Memory and Brain Microstructure after Mild Traumatic Brain Injury

Editor’s Choice

The authors investigated how working memory deficits relate to detectable WM microstructural injuries to discover robust biomarkers that allow early identification of patients with mild traumatic brain injury at the highest risk of working memory impairment. Multi-shell diffusion MR imaging was performed on a 3T scanner with 5 b-values. Diffusion metrics of fractional anisotropy, diffusivity and kurtosis (mean, radial, axial), and WM tract integrity were calculated. Auditory-verbal working memory was assessed using the Wechsler Adult Intelligence Scale. ROI analysis found a significant positive correlation between axial kurtosis and Digit Span Backward in mild traumatic brain injury mainly present in the right superior longitudinal fasciculus, which was not observed in healthy controls.

Abstract

BACKGROUND AND PURPOSE

Altered Relationship between Working Memory and Brain Microstructure after Mild Traumatic Brain Injury
TBSS results show a significant positive correlation between AK and DSB. The mean FA skeleton (green) is overlaid on the mean FA map. Significantly correlated voxels (corrected P < .05) are shown in the heat map overlay in the right SLF in the MTBI group (A), but are not seen in the HC group (B).

Working memory impairment is one of the most troubling and persistent symptoms after mild traumatic brain injury (MTBI). Here we investigate how working memory deficits relate to detectable WM microstructural injuries to discover robust biomarkers that allow early identification of patients with MTBI at the highest risk of working memory impairment.

MATERIALS AND METHODS

Multi-shell diffusion MR imaging was performed on a 3T scanner with 5 b-values. Diffusion metrics of fractional anisotropy, diffusivity and kurtosis (mean, radial, axial), and WM tract integrity were calculated. Auditory-verbal working memory was assessed using the Wechsler Adult Intelligence Scale, 4th ed, subtests: 1) Digit Span including Forward, Backward, and Sequencing; and 2) Letter-Number Sequencing. We studied 19 patients with MTBI within 4 weeks of injury and 20 healthy controls. Tract-Based Spatial Statistics and ROI analyses were performed to reveal possible correlations between diffusion metrics and working memory performance, with age and sex as covariates.

RESULTS

ROI analysis found a significant positive correlation between axial kurtosis and Digit Span Backward in MTBI (Pearson r = 0.69, corrected P = .04), mainly present in the right superior longitudinal fasciculus, which was not observed in healthy controls. Patients with MTBI also appeared to lose the normal associations typically seen in fractional anisotropy and axonal water fraction with Letter-Number Sequencing. Tract-Based Spatial Statistics results also support our findings.

CONCLUSIONS

Differences between patients with MTBI and healthy controls with regard to the relationship between microstructure measures and working memory performance may relate to known axonal perturbations occurring after injury.

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Editor’s Choice: Altered Relationship between Working Memory and Brain Microstructure after Mild Traumatic Brain Injury
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Jeffrey Ross
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