| The structural changes that arise as brains age influence their functionality. In many cases, the anatomical degradation simply leads to normal aging. In others, the degeneration is large enough to cause neurological disorders (e.g. Alzheimer's disease). Both the structure and functional activity can be currently measured using noninvasive techniques, such as MRI and EEG. However, a full theoretical scheme linking structural and functional degradation is still lacking. Here, we present a neural mass model that bridges both levels of description and that fully describes experimentally observed multichannel EEG recordings. We focus our attention in the dominant frequency of the signals at different electrodes and in the correlation between specific electrode pairs, measured via the phase lag index (PLI). Our model allows us to study the influence of different structural connectivity pathways, independently of each other, on the normal and aberrant aging of brains. In particular, we study in detail the effect of the thalamic input in cortical structures, of the long-range connectivity between cortical regions, and of the short-range coupling within cortical areas. Once the influence of each type of connectivity is understood, we characterize the regions of the parameter space that are compatible with the recordings observed in three different populations: young, healthy elderly subjects and mild cognitive impaired patients. Our results show that a fine tuning of the different types of connectivity is needed to maintain a healthy functioning state of the brain independently of its age. |
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