Metabolic alterations in corpus callosum may compromise brain functional connectivity in MTBI patients: an 1H-MRS study.

After clinical resolution of signs and symptoms of mild traumatic brain injury (MTBI) it is still not clear if there are residual abnormalities of structural or functional brain networks. We have previously documented disrupted interhemispheric functional connectivity in 'asymptomatic' concussed individuals during the sub-acute phase of injury. Testing of 15 normal volunteers (NV) and 15 subacute MTBI subjects was performed within 24h of clinical symptoms resolution and medical clearance for the first stage of aerobic activity. In this MRS study we report: (a) both in the genu and splenium of the corpus callosum NAA/Cho and NAA/Cr ratios were significantly (p<0.05) lower in MTBI subjects shortly after the injury compared to NVs, and (b) the metabolic ratio NAA/Cho in the splenium significantly correlated with the magnitude of inter-hippocampal functional connectivity in normal volunteers, but not in MTBI. This novel finding supports our hypothesis that the functional disruption of interhemispheric brain networks in MTBI subjects results from compromised metabolic integrity of the corpus callosum and that this persists despite apparent clinical return to baseline.