Hypothesis 1: Veterans with mTBI will generate abnormal MEG slow-waves during the baseline MEG exam. Voxel-wise MEG slow-wave source imaging will show significantly higher sensitivity than conventional MRI in identifying the loci of injury on a single-subject basis. The test-retest reliability of MEG slow-wave source imaging is expected to be high, with intra-class correlation coefficient (ICC) 0.75 between two sequential MEG exams.