Magnetoencephalographic analysis of cortical activity in Alzheimer's disease: a pilot study

Objectives: In the present study, MEG was used to analyze spectral power an d reference-free coherence in patients with probable Alzheimer's disease (A D). Methods: Sixty-one channel MEG was recorded in 5 AD patients and 5 age-matc hed controls at rest with eyes open and eyes closed, as well as during the performance of two different mental tasks. Artefact-free epochs were select ed for the analysis of power and coherence: values in each of 5 4-Hz wide f requency bands ranging from 2 to 22 Hz. Results: In AD patients, the absolute low frequency magnetic power was sign ificantly and rather diffusely increased relative Co controls with a fronto -central maximum. High frequency power values were significantly decreased over the occipital and temporal areas. Reactivity to eye-opening and mental tasks was reduced in the patient group. Relative to controls, a general de crease of MEC coherence values, including all frequencies analyzed, was fou nd in AD patients. Conclusions: These observations confirm the pattern of changes in spectral power and reactivity known from EEG studies and suggest that coherence decr eases in AD patients are widespread and include frequencies outside the alp ha band. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.