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.