Age at First Exposure to Football Is Associated with Altered Corpus Callosum White Matter Microstructure in Former Professional Football Players

Abstract

Youth football players may incur hundreds of repetitive head impacts (RHI) in one season. Our recent research suggests that exposure to RHI during a critical neurodevelopmental period prior to age 12 may lead to greater later-life mood, behavioral, and cognitive impairments. Here, we examine the relationship between age of first exposure (AFE) to RHI through tackle football and later-life corpus callosum (CC) microstructure using magnetic resonance diffusion tensor imaging (DTI). Forty retired National Football League (NFL) players, ages 40-65, were matched by age and divided into two groups based on their AFE to tackle football: before age 12 or at age 12 or older. Participants underwent DTI on a 3 Tesla Siemens (TIM-Verio) magnet. The whole CC and five subregions were defined and seeded using deterministic tractography. Dependent measures were fractional anisotropy (FA), trace, axial diffusivity, and radial diffusivity. Results showed that former NFL players in the AFE <12 group had significantly lower FA in anterior three CC regions and higher radial diffusivity in the most anterior CC region than those in the AFE ≥12 group. This is the first study to find a relationship between AFE to RHI and later-life CC microstructure. These results suggest that incurring RHI during critical periods of CC development may disrupt neurodevelopmental processes, including myelination, resulting in altered CC microstructure.

Keywords: American football; age at first exposure; corpus callosum; diffusion tensor imaging; repetitive head impacts.

FIG. 1.

Tractography of the corpus callosum. The corpus callosum was subdivided into five regions containing commissural fibers of prefrontal (region I), premotor and supplementary motor (region II), primary motor (region III), sensory (region IV), and parietal, temporal and occipital cortical (region V) areas. Tracts were obtained using deterministic (streamline) tractography to trace fiber paths through the regions of interest. Color image is available online at www.liebertpub.com/neu

FIG. 2.

Scatter plots illustrating fractional anisotropy (FA) in corpus callosum regions I, II, and III, and radial diffusivity (RD) in region I. Those with an age of first exposure to tackle football prior to age 12 had significantly lower FA in Regions I, II, and III, and higher RD in Region I, than those who began playing football at age 12 or later. Error bars signify one standard deviation from the mean. Color image is available online at www.liebertpub.com/neu