Fig 13: Windows of sensitivity for the regulation of brain gene expression by thyroid hormone during the postnatal period in the rat. A few examples of genes sensitive to thyroid hormone during the postnatal period is shown to illustrate the windows of sensitivity of the regulated genes. Other genes that are sensitive in the fetal period and in the adult are not shown in this figure. The windows of sensitivity of the myelin genes are different for each brain region, so that in the more caudal regions (for example brain stem and cerebellum) the window is earlier than in the frontal regions (cortex).