dr. daniel perl.he brain tissue repository at the uniformed services university of the health sciences, the military medical school in bethesda, maryland. perl also wondered whether some torments of war might be rooted in an undiscovered kind of brain injury caused by the supersonic pressure wave of high explosives. >> daniel perl: that started in world war i, and we had the whole issue of shell shock. and then, in world war ii, we had battle fatigue. then, in korea, we had p.t.s.d. i mean, these were all expressions of responses to being in warfare, much of it being exposed to blast. and we knew nothing about what was going on in the brain. >> pelley: perl's team sliced brain tissue from eight veterans and examined the tissue under a microscope, rare for its power. that doesn't look like the one i had in high school. >> perl: no, it's not. >> pelley: perl says his microscope is thousands of times more powerful than the best m.r.i., and it helped them discover this previously unknown form of brain inj