EEG COHERENCE IN ALZHEIMERS-DISEASE

EEG coherence can be used to evaluate the functionality of cortical co nnections and to get information about the synchronization of the regi onal cortical activity. We studied EEG coherence in patients affected by clinically probable Alzheimer's disease (AD) in order to quantify t he modifications in the cortico-cortical or cortico-subcortical connec tions. The EEGs were recorded in IO AD patients (with mild or moderate degrees of dementia) and in 10 normal age-matched subjects, at rest a nd eye-closed, from 16 electrodes with linked-ears reference. Spectral parameters and coherence were calculated by a multichannel autoregres sive model using 50 artifact-free epochs, 1 s duration each. Alpha coh erence was significantly decreased in 6 patients, the decrease being m ore accentuated in the area near the electrode taken into account; a s ignificant delta coherence increase was found in a few patients betwee n frontal and posterior regions. The AD group showed a significant dec rease of alpha band coherence, in particular in temporo-parieto-occipi tal areas, more evident in patients with a more severe cognitive impai rment. These abnormalities could reflect two different pathophysiologi cal changes: the alpha coherence decrease could be related to alterati ons in cortico-cortical connections, whereas the delta coherence incre ase could be related to the lack of influence of subcortical cholinerg ic structures on cortical electrical activity. (C) 1998 Elsevier Scien ce Ireland Ltd.