This phenomenon, illustrated in Figure 6, is sometimes referred to as retrogenesis (Reisberg et al., 1999), where deficits appear first in systems that are last to mature during development. As is visually evident in the time-lapse maps, the maturational sequence proceeds in a pattern opposite to the classical neurodegenerative sequence in AD. This has led to some speculation that the earliest maturing cortices may be insulated by thick myelin sheaths and neuroglia that may protect them from neuroinflammation or degeneration, as plaques and tangles build up in later life. Normal cortical maturation may therefore be especially relevant to the future risk for AD; early cortical myelination may contribute to a cognitive reserve that delays the onset of symptoms in those at risk.
