morphological and distributional criteria

At present, however, the biological bases for early deterioration of global and regional gray matter volumes remain unclear. Thus, gray matter atrophy represents a midlife preclinical predictor of cognitive aging. Individuals differ in rates of age-related brain atrophy, with accelerated gray matter loss associated with earlier progression to dementia ( Whitwell et al., 2008). On average, reductions in gray matter volume begin around age 35 and accelerate thereafter ( Fjell et al., 2013 Hedman et al., 2012), associating with concomitant and future declines in cognitive function ( Burgmans et al., 2009 Fjell and Walhovd, 2010 Kramer et al., 2007). These changes include reductions in total brain and gray matter volume and in white matter integrity that accompany advancing age ( Burgmans et al., 2009 DeCarli et al., 2005 Fjell et al., 2013 Kennedy and Raz, 2009 Raji et al., 2012 Raz et al., 2005 Ryan et al., 2011). Preclinical changes in brain morphology precede and may contribute to cognitive declines among healthy aging individuals, as well as predict risk for dementia ( Burgmans et al., 2009 den Heijer et al., 2006 Driscoll et al., 2009 Kramer et al., 2007 Persson et al., 2012 Raz et al., 2005 Walhovd et al., 2011). Understanding factors that account for individual differences in cognitive aging is critical because age-related impairments in cognitive function confer risk for dementia ( Barberger-Gateau et al., 1999 De Lepeleire et al., 2004), injuries ( Sattin, 1992), hospitalization, and death ( Bennett, 1997). Trajectories of cognitive aging are heterogeneous, however, with some individuals showing minimal declines and others more precipitous deterioration ( Raz et al., 2005). Typically, these cognitive declines begin in the late 20s and progress across adulthood ( Salthouse, 2004). Aging engenders declines in multiple cognitive domains, including episodic and working memory, attention, and executive functioning ( Salthouse, 2004).

Morphological and distributional criteria