Figure 2.

Two ways in which dysfunction of NDD genes can dysregulate critical periods. A critical period is shown here as the timeframe between “1” and “2”. (A) In this scenario, the critical period is caused by external factors (blue bar) not related to the NDD gene and expression of the NDD gene in wild-type is not necessarily atlered before, during or after the critical period (red area). However, the NDD gene plays a role downstream of these external factors and is necessary for phenotypic change to take place, thereby indirectly regulating not the occurrence but the outcome of the critical period. Hence, dysfunction of the gene leads to an impaired critical period. (B) Increased NDD gene expression (red area) directly regulates the critical period and causes it to occur, independent of external factors. Therefore, dysfunction of the NDD gene causes the critical period to be absent completely. (C) In both scenarios, the NDD gene is necessary for the phenotypic change that takes place during the critical period (“WT” vs “KO”), represented here by maturation of spine morphology.