Effects of memory training on cortical thickness in the elderly
Introduction
Plasticity and reorganization of neural systems have recently been studied in both animals and humans (Buonomano and Merzenich, 1998, DeFelipe, 2006, Jones et al., 2006, Martin et al., 2000). Advances in neuroimaging techniques have enabled tracking of behavioral changes to alterations in specific brain regions in vivo (Draganski et al., 2006, Haier et al., 2009). Accumulating evidence suggests that the brain's potential to adapt and change is life-long (Johansson, 2004, Pascual-Leone et al., 2005). However, the mechanisms by which such alterations are effectuated are poorly understood, and little is known about their functional specificity. Structural grey matter (GM) changes measured by MRI have been reported in young subjects from days to months after learning to juggle (Draganski and May, 2008, Driemeyer et al., 2008). This finding was also replicated in older subjects, suggesting intact neuroplasticity in advanced age (Boyke et al., 2008). The same group also reported structural alterations in students in response to extensive studying (Draganski et al., 2006). Thus, training visuo-motor skills and learning abstract information seems to induce structural brain changes in both young and older subjects.
To answer questions of domain specificity, it is important to address different functional domains. Memory, a spectrum of cognitive functions inextricably coupled to everyday function, is associated with increasing concern among the aging population (Anderson and McConnell, 2007, National Council on the Aging, 2000), and memory complaints are reported by up to 50% of adults aged 64 and over (Reid and MacLullich, 2006). Furthermore, aging is associated with both progressive structural alterations (Fjell et al., 2009b, Jernigan et al., 2001, Raz et al., 2004, Raz et al., 2007, Salat et al., 2004, Walhovd et al., 2005, Walhovd et al., 2009, Westlye et al., 2009, Westlye et al., in press-aa, Westlye et al., in press-bb) and functional decline across multiple cognitive domains (Mahncke et al., 2006, Raz and Rodrigue, 2006). Population studies have indicated that mental exercise may slow the rate of cognitive decline (Valenzuela and Sachdev, 2006a) and decrease the risk of dementia (Valenzuela and Sachdev, 2006b). Hence, the role of mental exercise has gained much attention in preventive aging research (Rebok et al., 2007). However, knowledge about protective effects of mental exercise is sparse, and it is not known whether engaging in cognitively stimulating activities changes aging-related structural cerebral trajectories.
Most behavioral studies of memory improvement have been strategy-based, focusing on learning a specific mnemonic technique known as the MoL (Bower, 1970). Studies employing this technique have found associated changes in brain activation and neurochemistry (Kondo et al., 2005, Nyberg et al., 2003, Valenzuela and Sachdev, 2006a). However, no experimental study so far has been conducted to investigate whether such memory training can induce macro-structural changes in the brain. Further, visuo-motor training has been shown to induce macro-structural changes in elderly, but for cognitive training this has been demonstrated in young only. The aim of the present MRI study was to determine whether engaging in an 8-week memory training program would improve memory performance and induce regional changes in longitudinal cortical thickness trajectories in middle aged and older adults.
Section snippets
Sample
Table 1 summarizes baseline demographic and neuropsychological characteristics of the participants included in the analyses. Fig. 1 gives an overview of the recruitment and group assignment process. Volunteers were recruited through a local newspaper ad and screened by a structured interview before inclusion. All included participants reported to be right-handed, native Norwegian speakers, not concerned about their own memory function, not using medications known to interfere with cognitive
Memory performance changes
Table 1 summarizes neuropsychological characteristics and results from independent samples t-tests comparing the two groups at tp1. No significant group differences were found at tp1. The mean source memory task scores for the training and control group were 0.52 (Standard Error (SE) = 0.03) and 0.57 (SE = 0.02), respectively, at tp1, and 0.73 (SE = 0.03) and 0.62 (SE = 0.03), respectively, at tp2. Repeated measures ANOVA revealed a significant group × time interaction (Greenhouse–Geisser corrected, F
Discussion
There were three main findings in the present study: (1) Intensive source memory training specifically improved memory performance on a source memory task, (2) memory training induced longitudinal short-term regional effects on cortical thickness, indicating that the intervention influenced the age-related trajectories, and (3) regional cortical thickening was positively correlated with memory improvement. Thus, degree of cortical change was directly related to improvement rate in source memory
Acknowledgments
The Norwegian Research Council (177404/W50) to K.B.W., (175066/D15) to A.M.F. The Medical student research program to A.E. We thank the participants, and Håkon Grydeland and Inge Amlien for help with data acquisition.
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