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Figure 3-6 This map (left frontal view)shows age effects on gray matter densityon the lateral surface of the brain betweenchildhood and old age. Shades of greento yellow represent positive partial regressioncoefficients for the quadratic term(U-shaped curves with respect to age), andshades of blue, purple, and pink representnegative partial regression coefficients(inverted U-shaped curves). Regionsshown in red correspond to regressioncoefficients that have significant positivenonlinear age effects at a threshold of P= 0.0000008, and regions shown in whitecorrespond to significant negative nonlinearage effects at a threshold of P = 0.01.The pattern of nonlinear age effects wassimilar in the left and right (not shown)hemispheres except that none of the negativenonlinear age effects in the right posteriortemporal lobe reached a thresholdof P = 0.01. Scatterplots of age effectswith the best fitting quadratic regressionline are shown for sample surface pointsin the superior frontal sulcus (top) and thesuperior temporal sulcus (bottom) representativeof the positive (U-shaped) andnegative (inverted U-shaped) nonlinearage effects. Gray matter proportion withinthe 15-mm sphere surrounding the samplesurface point (matched across subjects) isshown on the Y-axis. See color insert.(Sowell et al., 2003a.)Mapping Adolescent Brain Change 69