Lesion deficits are complicated by fibers and suppression

The classic inference that a focal lesion proves a region 'does' a function is complicated because damage may destroy fibers of passage rather than the critical neurons, and lost function can sometimes be recovered by a second lesion—e.g., ablating primary visual cortex causes blindness, but a further lesion in the superior colliculus can restore some vision because the colliculus normally suppresses retinal information reaching V1.