# A one year longitudinal study of cortical myelination changes following pediatric mild traumatic brain injury

## TL;DR

This study found that pediatric mild traumatic brain injury has little to no lasting effect on brain myelination, which is primarily influenced by age and hemisphere differences.

## Contribution

The study provides longitudinal evidence that pmTBI does not significantly alter cortical myelination development.

## Key findings

- Myelin content increased with age and showed stronger changes in the left hemisphere.
- pmTBI showed temporary myelination changes, but these did not persist after sensitivity analyses.
- Females had higher myelin content than males across the study.

## Abstract

•Pediatric mild traumatic brain injury has little to no effect on myelination.•Developmental myelination has a strong correlation with age.•Changes in myelination were greater in the left relative to right hemisphere.

Pediatric mild traumatic brain injury has little to no effect on myelination.

Developmental myelination has a strong correlation with age.

Changes in myelination were greater in the left relative to right hemisphere.

The impact of pediatric mild traumatic brain injury (pmTBI) on cortical (i.e., grey matter) myelination is not yet understood, especially for interactions with neurodevelopment. The current study examined the impact of pmTBI on cortical myelination relative to healthy controls (HC) by estimating myelin content using the T1w/T2w ratio method. Data were obtained from pmTBI (N = 217) participants at approximately 7 days (Visit 1 [V1]), 4 months (Visit 2 [V2]), and 1 year (Visit 3 [V3]) post-injury, with equivalent sampling points for age and sex-matched HC (N = 180). Clinical results suggested only partial recovery from post-concussive symptoms from V1 to V3, with similar incomplete recovery of sleep, functional outcomes, behavior, and long-term memory. Myelin content increased with chronological age and as a function of individual aging across study visits in a hemisphere specific fashion (left > right), most visibly within the posterior parietal lobe. Myelin content was also greater for females relative to males. There was evidence of both a reduction in myelination within the posterior parietal cortex for the pmTBI group at 4 months post-injury, as well as evidence of increased myelination within the left prefrontal cortex at one-year post-injury. However, neither of these findings survived various sensitivity analyses, suggesting that there were minimal effects of pmTBI on cortical myelin content in general. In summary, although rapid changes in myelin content existed as a function of neurodevelopment, there was little evidence to suggest that pmTBI permanently altered cortical myelin development trajectories.