Figure: 3 Frequency (Grade 1~4) of SPD appearance in molecular layer of hippocampal dentate gyrus (a). Grade 4 (30yrs, male): >100 (b). Grade 3 (44yrs, male): 50 ~ 100 (c). Grade 2 (32yrs, female): 10 ~ 50 (d) Grade 0 (24yrs, male): none