Human brain volume: What's in the genes?

The human brain continues to grow considerably after birth. Compared to measurements taken at birth (mean, SD was 34.9, 1.1 cm), head circumference was found to increase by more than 30% in the first year (46.6, 1.3 cm); between 1 and 4 years of age it increased by another 9% (50.9, 1.4 cm) and between 4 and 8 years by an additional 4% (53.4, 1.4 cm) in a normal cohort (Gale, O'Callaghan, Bredow, & Martyn, 2006). Magnetic resonance imaging (MRI) research has shown that at 6 years of age total cerebral volume has reached 95% of its adult volume (Giedd et al., 1999). However, the brain continues to show dynamic changes from childhood into adulthood in overall gray and white matter and in subcortical structures. In early adolescence gray matter starts to decrease (Giedd et al., 1999), whereas overall white matter volume still increases (Bartzokis et al., 2001; Giedd et al., 1999; Paus et al., 1999). Also, subcortical structures show developmental changes after childhood. For instance, the thalamus and caudate nucleus decrease with age (Sowell, Trauner, Gamst, & Jernigan, 2002) and the posterior hippocampus increases with age, whereas the anterior hippocampus decreases with age (Gogtay et al., 2006) (for a review on brain maturation, see Toga, Thompson, & Sowell, 2006).