Histological examination of (A, C) left (BBB-opened) and (B, D) corresponding right (no ultrasound) hippocampi. No microscopic tissue damage was observed in the BBB-opened hippocampus at 0.51 MPa (A), same as in the intact right hippocampus on the same section (B). Minor microhemorrhage is noticeable in one location (box) in the hippocampus sonicated at 0.84 MPa (C), compared to no damage in nonsonicated hippocampus (D). The insert shows magnified image of the region in the box. Scale bar represents 1 mm.