Furthermore, Participants with a Ten Or More IQ Point Increase Showed a Non-Significant

Skirrow et al.

Appendix e-1 – Longitudinal changes in brain tissue volumes: There are different developmental trajectories over time for both gray and white matter, which were also significant in this cohort. No significant changes in total brain size and ICV were found across the follow-up period, while gray matter volume decreased by 45 ml (t=3.1, p=0.005) and white matter volume increased by 42 ml (t=9.3, p<0.001). The direction and magnitude of the latter changes is in keeping with maturational changes across adolescence.e1 However, it is important to bear in mind that different MRI scanners were used at baseline and follow-up, which can influence tissue segmentation and volumes.

Furthermore, participants with a ten or more IQ point increase showed a non-significant increase in gray matter volume (6 ml) compared to significant losses of 77 ml in those without such IQ change. White matter volume increases were seen in both groups. This suggests that the group of individuals with a greater IQ gain had a less pronounced gray matter loss over the period of follow-up. This finding is in agreement with longitudinal studies of IQ variability in healthy adolescents showing a longer period of cortical thickness increase in individuals with superior IQ compared to those with average intelligence. e2 A recent longitudinal studye3 extended these findings to adulthood (20-35 years) showing more pronounced cortical thickening in medial temporal cortex and attenuated frontal cortex thinning in individuals with IQ>110 compared to those with average or below average IQ. The physiological substrate of these changes is currently not known but has been attributed to cortical plasticity.e3

Conversely, accelerated focal gray matter volume change has been associated with cognitive decline in longitudinal cohort studies of individuals at risk of psychosise4,e5 and verbal IQ decline.e6

e-References:

e1. Lenroot, R. K. and J. N. Giedd. Brain development in children and adolescents: insights from anatomical magnetic resonance imaging. Neurosci.Biobehav.Rev. 30.6 (2006): 718-29.

e2. Shaw P, Greenstein D, Lerch J, et al. Intellectual ability and cortical development in children and adolescents. Nature (2006) 440:676-679.

e3. Brans RG, et al. Brain plasticity and intellectual ability are influenced by shared genes. J Neurosci. (2010):30(16):5519-24.

e4.Thompson, P. M., et al. Mapping adolescent brain change reveals dynamic wave of accelerated gray matter loss in very early-onset schizophrenia. Proc.Natl.Acad.Sci.U.S.A 98.20 (2001): 11650-55.

e5. Gothelf, D., et al. COMT genotype predicts longitudinal cognitive decline and psychosis in 22q11.2 deletion syndrome. Nat.Neurosci. 8.11 (2005): 1500-02.

e6. Gothelf, D., et al. Developmental trajectories of brain structure in adolescents with 22q11.2 deletion syndrome: a longitudinal study. Schizophr.Res. 96.1-3 (2007): 72-81.