In an earlier study from the NIMH sample, males had a more rapid increase in amygdala size, while the hippocampus grew more quickly in females (Giedd et al., 1997). Suzuki and colleagues also found sexual dimorphism in the growth of the hippocampus, but in this case, they reported more pronounced growth in males. They measured age and sex effects on volumes of the hippocampus and parahippocampus in a group of 23 adolescents (13-14 yrs age, 10 male) and 30 young adults (18-21 years, 15 males)(Suzuki et al., 2005). Hippocampal volumes were significantly larger in the adult males than in the adolescents, but there were no differences in females. The authors speculated that the discrepancy could be related to the older age of participants in this study compared to previous reports, suggesting that hippocampal growth may occur earlier in girls than boys, consistent with the pattern seen in other brain regions (Lenroot et al., 2007).
