Frontal shift of posterior alpha activity is correlated with cognitive impairment in early Alzheimer's disease: a magnetoencephalography-beamformer study.
BACKGROUND
Induced-oscillatory activity is considered a key factor for understanding functional processes in the brain. Magnetoencephalography (MEG) can measure oscillatory activity non-invasively with higher spatial resolution than electroencephalography (EEG). However, MEG has rarely been used to explore functional abnormalities that may represent state markers in patients with Alzheimer's disease (AD).


METHODS
Thirteen patients with early AD and 14 age-matched normal controls participated in the present study. Magnetoencephalography activity was acquired during eyes-open and eyes-closed states. Alpha event-related synchronization (ERS) after eye closing was calculated and its cortical sources superimposed on each individual's magnetic resonance imaging (MRI) scan. The resulting functional image was converted into a Talairach-transformed anatomical brain image and group comparisons were made. We also assessed correlations between cortical ERS sources showing significant between-group differences in alpha activity and external clinical parameters, especially measures of cognitive function.


RESULTS
The averaged alpha ERS after eye closing appeared dominantly in posterior brain regions in both patients with AD and healthy controls. However, there was a significant increase in alpha ERS in frontal regions, maximal over the prefrontal cortex, in patients with AD relative to controls, indicating a frontal shift of the posterior dominant MEG alpha rhythm in AD patients. This frontal ERS source in the alpha band was negatively correlated with Mini-Mental State Examination scores in the AD patient group.


CONCLUSIONS
The findings indicate that a frontal shift of alpha ERS elicited by an eyes-open/eyes-closed paradigm may be an early brain electromagnetic change in patients with AD, probably representing a physiological state marker of the disease. Furthermore, the results confirm that the beamformer with group comparison analysis is a useful tool with which to explore functional processes in the brain, as indicated by oscillatory activity changes.
Ishii
Ryouhei
R
Department of Psychiatry, Osaka University Graduate School of Medicine, Suita City, Osaka, Japan. ishii@psy.med.osaka-u.ac.jp
Canuet
Leonides
L
Kurimoto
Ryu
R
Ikezawa
Koji
K
Aoki
Yasunori
Y
Azechi
Michiyo
M
Takahashi
Hidetoshi
H
Nakahachi
Takayuki
T
Iwase
Masao
M
Kazui
Hiroaki
H
Takeda
Masatoshi
M
D000368:Aged; D000369:Aged, 80 and over; D000513:Alpha Rhythm; D000544:Alzheimer Disease / Q000175:diagnosis* / Q000503:physiopathology*; D003072:Cognition Disorders / Q000175:diagnosis* / Q000503:physiopathology*; D003344:Cortical Synchronization / Q000502:physiology; D005260:Female; D005583:Fourier Analysis; D005625:Frontal Lobe / Q000503:physiopathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D015225:Magnetoencephalography / Q000295:instrumentation*; D008297:Male; D017397:Prefrontal Cortex / Q000503:physiopathology*; D012016:Reference Values; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*