In children, FPN is less often activated and preferentially, caudate nucleus (CN) and insula are activated. In adolescents, wide rangig areas are activated. Very young children cannot access CHC corticohippocampal cortical networks or FPN which are not developed as well, and typically "react"; by age 8 they may proactively access hippocampal contextual declarative (episodic and semantic) systems and FPN which is developing. before that they do have working memory and can retrieve some information as it is needed for the moment. Later, these systems in combination are part of the working memory system.
As children develop, they increasingly develop capacity to react to contextual cues in their environment as their form of "cognitive control." Later, they shift to recrutiing cognitive systems as they require it, and later proactively recruiting cognitive systems.
Point is that over development, more brain systems are recruited into "cognitive control" but the systems remain dissociable, there is no cognitive control.
Author notes that "composite score " of DS and letter number LN sequences are poor since they mask the findings of each. Lexak says "composite scores have no place in neuopsychological assessment." The correlation r between ds and LN is 0.49
Authors note that LN depends on procedurizing knowledge of letters and numbers as happens by middle childhood. FPN is the flexible hub, and activates other brain areas as needed.