Neuromagnetic correlates of aging evidence from resting state and event-related analyses

Abstract

In this thesis I report three magnetoencephalography (MEG) studies that investigated age-related alterations in neuromagnetic activity during either a cognitive task or during the resting state using different methodological approaches.The main goal of study 1 was to assess whether the hippocampal-associated activation pattern during the transverse patterning task changes with increasing age and whether it is related to cognitive performance. The results suggest that in non-pathological aging, hippocampal function does not decrease with age but is related to individual performance in memory and executive function.Study 2 aimed at exploring age-related alterations in the intensity and distribution of generators of focal magnetic slow waves and associations between cognitive performance and sources of low-frequency activity in the brain. Generators of focal magnetic slow waves in the delta frequency range were localized by employing a single moving dipole model and by calculating dipole densities in anatomically defined cortical regions (frontal, central, temporal and parieto-occipital). Results revealed a pronounced negative age effect, i.e. dipole density decreases with increasing age. Regarding the association between dipole density and cognitive performance, no significant relationship could be found which lead us to the conclusion that slow waves are specifically associated with the disease process of Morbus Alzheimer and are not linked to age and pathological states per se in healthy individuals.In study 3, age-related alterations in functional resting state brain networks and their behavioral significance were investigated. Resting state recordings are characterized by widely distributed networks of coherent brain activations. In this study, the resting state networks were analyzed with respect to the directionality of the information flow between distant cortical regions using partial directed coherence (PDC). Significant age-related alterations of functional resting state connectivity were found that are mainly characterized by reduced information input into the posterior cingulum/precuneus region together with an enhanced information flow to the medial temporal lobe. This was the first study to show age-related alterations in subsystems of the resting state network that are furthermore associated with cognitive performance.