, 2002; Duan et al., 2003; Peters et al., 2008; Dumitriu et al., 2010) and rats (Bloss et al., 2011, 2013). This change in spines represents the most consistent age-related alteration of cellular morphology reported in the frontal cortical literature, and is illustrated in Fig. 3. With respect to the dendritic arbor, IWR-1 order significant regression only occurs at the level of the apical

dendrites in the PFC of aged humans (de Brabander et al., 1998), monkeys (Cupp & Uemura, 1980; Duan et al., 2003; Kabaso et al., 2009) and male rodents (Grill & Riddle, 2002; Markham & Juraska, 2002). The regression of terminal dendrites and synaptic loss that occur during aging probably affects dendritic excitability and plasticity processes in the PFC, thus contributing to the age-related decline in learning and working memory. In support of this, there is

a decline in spine numbers and reduced thin spine volumes in area 46 in monkeys. This reduction was shown to correlate with acquisition and performance on a DNMS task (Peters et al., 1998b; Dumitriu et al., 2010). Additionally, a Selleckchem Idelalisib recent study was able to show that there is a correlation between the age-related overactivation of protein kinase C, the length of basal dendrites and working memory performance in aged rats (Brennan et al., 2009), suggesting that altered protein kinase C activity may be the basis of some of the anatomical and functional deficits found in aged animals. Despite cortical volume and cellular changes reported in the frontal cortex of older adults, many fMRI studies report areas of overactivation, greater bilateralization or recruitment of additional structures in PFC areas of older adults during performance of certain

cognitive tasks (e.g., Spreng et al., 2010; Morcom & Friston, 2012; Spaniol & Grady, 2012). This is a phenomenon thought to reflect compensatory mechanisms and, in support Masitinib (AB1010) this hypothesis, greater activation of frontal areas has been shown to be associated with better performance (Grady et al., 2005). Thus, it is plausible that plastic mechanisms in the PFC compensate for changes occurring in the PFC and other parts of the brain in older adults, thereby contributing to preservation of cognitive function. In support of this idea, under some circumstances accurate retrieval of autobiographical events in older adults also show a similar pattern (as outlined previously). That is, during retrieval the hippocampi of older adults show bilateral activation whereas young adults show hippocampal activation lateralized to the left hemisphere (Maguire & Frith, 2003). In contrast to gray matter volumes that decrease linearly with age, white matter volume change across the lifespan follows a parabolic shape, with the largest volumes in the mid-fifties and an accelerated decline after 65 years of age (Allen et al., 2005; Gunning-Dixon et al., 2009; Bennett et al., 2010; Giorgio et al., 2010; Malykhin et al., 2011).