Neurofunktionelle Grundlagen der Steuerung episodisch-assoziativer Gedächtnisfunktionen und ihre Veränderung im Altersverlauf

The ability to decide deliberately which event or thought is worth to be remembered or can be forgotten alternatively is a basic foundation of regulating one’s memory. Active suppression is part of this self-regulative functioning and for this reason also part of executive operations. Within a so-called think/no-think paradigm (subjects have either to remember or to suppress former studied words) a network model of memory control (Anderson & Green, 2001; Anderson et al., 2004a) has been developed: the dorsolateral prefrontal cortex seems to play a crucial role in controlling the hippocampus while retrieving neutral episodic memory contents. On behavioural level the authors detected that words that should be remembered during the think/no-think phase as well as words that are only learned initially and retrieved in the end are significantly better stored in memory than words that should be suppressed. In my project I adapted this paradigm and compared the behavioural data of 15 younger (mean age 23.5 years) and 15 older healthy adults (mean age 64.7 years). To further investigate the neural underlyings of this possible suppression effect we measured the brain activation of these 30 healthy subjects with functional magnetic resonance imaging (fMRI) while completing the think/no-think paradigm. Additionally, an extensive neuropsychological test battery was conducted. Hence, the comparability of the groups was examined and especially the executive functions of the older and younger participants were assessed. Within the behavioural data no suppression effect as predicted by Anderson and Green (2001) could be replicated in neither of the two groups. However, there was an executive process during the think/no-think procedure, as the imaging data suggest. The activation pattern found in this paradigm is discussed with regard to the behavioural and neuropsychological data, particularly those concerning executive functions, as well as the underlying networks of suppression as proposed by Anderson et al. (2004a) and the general neural substructures of aging. My results suggest a prefrontal network of cognitive control within the subsample of young participants similar to the finding of Anderson et al. (2004a). By dividing the elderly subjects of this study into two groups, the high-performing elderly showed a frontal network comparable to the younger ones with a dedifferentiation concerning the hemispheric asymmetry while the low-performing elderly showed no frontal activation at all at a comparable significance threshold. Thus, the results of the presented study are in accordance with former studies to frontal compensation and beginning dysfunction during healthy aging and give reason to further aging research related to cognitive control